深海游弋的鱼 – 第 47 页 – 智障儿童欢乐多

判断网页是通过PC端还是移动终端打开的

通过判断打开设备，跳转不同页面，可以根据 User-Agent 来区分：

if((navigator.userAgent.match(/(phone|pad|pod|iPhone|iPod|ios|iPad|Android|Mobile|BlackBerry|IEMobile|MQQBrowser|JUC|Fennec|wOSBrowser|BrowserNG|WebOS|Symbian|Windows Phone)/i))) {
    window.location.href = "";     //手机
} else {
    window.location.href = "";        //电脑
}

if((navigator.userAgent.match(/(phone|pad|pod|iPhone|iPod|ios|iPad|Android|Mobile|BlackBerry|IEMobile|MQQBrowser|JUC|Fennec|wOSBrowser|BrowserNG|WebOS|Symbian|Windows Phone)/i))) {

window.location.href = ""; //手机

} else {

window.location.href = ""; //电脑

}

也可以执行其他操作：

if((navigator.userAgent.match(/(phone|pad|pod|iPhone|iPod|ios|iPad|Android|Mobile|BlackBerry|IEMobile|MQQBrowser|JUC|Fennec|wOSBrowser|BrowserNG|WebOS|Symbian|Windows Phone)/i))) {
    alert('您正在通过手机访问');
} else {
    alert("您在PC端访问");
}

if((navigator.userAgent.match(/(phone|pad|pod|iPhone|iPod|ios|iPad|Android|Mobile|BlackBerry|IEMobile|MQQBrowser|JUC|Fennec|wOSBrowser|BrowserNG|WebOS|Symbian|Windows Phone)/i))) {

alert('您正在通过手机访问');

} else {

alert("您在PC端访问");

}

JS判断客户端是否是iOS或者Android手机移动端：

通过判断浏览器的 userAgent，用正则来判断手机是否是ios和Android客户端。代码如下：

<script type="text/javascript">
    var u = navigator.userAgent;
    var isAndroid = u.indexOf('Android') > -1 || u.indexOf('Adr') > -1; //android终端
    var isiOS = !!u.match(/\(i[^;]+;( U;)? CPU.+Mac OS X/); //ios终端
    alert('是否是Android：'+isAndroid);
    alert('是否是iOS：'+isiOS);
</script>

var u = navigator.userAgent;

var isAndroid = u.indexOf('Android') > -1 || u.indexOf('Adr') > -1; //android终端

var isiOS = !!u.match(/\(i[^;]+;( U;)? CPU.+Mac OS X/); //ios终端

alert('是否是Android：'+isAndroid);

alert('是否是iOS：'+isiOS);

</script>

下面一个比较全面的浏览器检查函数，提供更多的检查内容，你可以检查是否是移动端（Mobile）、ipad、iphone、微信、QQ等。

第一种：

<script type="text/javascript">
    //判断访问终端
    var browser={
        versions:function(){
            var u = navigator.userAgent, app = navigator.appVersion;
            return {
                trident: u.indexOf('Trident') > -1, //IE内核
                presto: u.indexOf('Presto') > -1, //opera内核
                webKit: u.indexOf('AppleWebKit') > -1, //苹果、谷歌内核
                gecko: u.indexOf('Gecko') > -1 && u.indexOf('KHTML') == -1,//火狐内核
                mobile: !!u.match(/AppleWebKit.*Mobile.*/), //是否为移动终端
                ios: !!u.match(/\(i[^;]+;( U;)? CPU.+Mac OS X/), //ios终端
                android: u.indexOf('Android') > -1 || u.indexOf('Adr') > -1, //android终端
                iPhone: u.indexOf('iPhone') > -1 , //是否为iPhone或者QQHD浏览器
                iPad: u.indexOf('iPad') > -1, //是否iPad
                webApp: u.indexOf('Safari') == -1, //是否web应该程序，没有头部与底部
                weixin: u.indexOf('MicroMessenger') > -1, //是否微信 （2015-01-22新增）
                qq: u.match(/\sQQ/i) == " qq" //是否QQ
            };
        }(),
        language:(navigator.browserLanguage || navigator.language).toLowerCase()
    }
    //使用方法：
    //判断是否IE内核
    if(browser.versions.trident){ alert("is IE"); }
    //判断是否webKit内核
    if(browser.versions.webKit){ alert("is webKit"); }
    //判断是否移动端
    if(browser.versions.mobile||browser.versions.android||browser.versions.ios){
        alert("移动端"); 
    }
</script>

//判断访问终端

var browser={

versions:function(){

var u = navigator.userAgent, app = navigator.appVersion;

return {

trident: u.indexOf('Trident') > -1, //IE内核

presto: u.indexOf('Presto') > -1, //opera内核

webKit: u.indexOf('AppleWebKit') > -1, //苹果、谷歌内核

gecko: u.indexOf('Gecko') > -1 && u.indexOf('KHTML') == -1,//火狐内核

mobile: !!u.match(/AppleWebKit.*Mobile.*/), //是否为移动终端

ios: !!u.match(/\(i[^;]+;( U;)? CPU.+Mac OS X/), //ios终端

android: u.indexOf('Android') > -1 || u.indexOf('Adr') > -1, //android终端

iPhone: u.indexOf('iPhone') > -1 , //是否为iPhone或者QQHD浏览器

iPad: u.indexOf('iPad') > -1, //是否iPad

webApp: u.indexOf('Safari') == -1, //是否web应该程序，没有头部与底部

weixin: u.indexOf('MicroMessenger') > -1, //是否微信（2015-01-22新增）

qq: u.match(/\sQQ/i) == " qq" //是否QQ

};

}(),

language:(navigator.browserLanguage || navigator.language).toLowerCase()

}

//使用方法：

//判断是否IE内核

if(browser.versions.trident){ alert("is IE"); }

//判断是否webKit内核

if(browser.versions.webKit){ alert("is webKit"); }

//判断是否移动端

if(browser.versions.mobile||browser.versions.android||browser.versions.ios){

alert("移动端");

}

</script>

检测浏览器语言

currentLang = navigator.language;   //判断除IE外其他浏览器使用语言
if(!currentLang){//判断IE浏览器使用语言
    currentLang = navigator.browserLanguage;
}
alert(currentLang);

currentLang = navigator.language; //判断除IE外其他浏览器使用语言

if(!currentLang){//判断IE浏览器使用语言

currentLang = navigator.browserLanguage;

}

alert(currentLang);

第二种：

if (/(iPhone|iPad|iPod|iOS)/i.test(navigator.userAgent)) {
    //alert(navigator.userAgent);  
    window.location.href ="iPhone.html";
} else if (/(Android)/i.test(navigator.userAgent)) {
    //alert(navigator.userAgent); 
    window.location.href ="Android.html";
} else {
    window.location.href ="pc.html";
};

if (/(iPhone|iPad|iPod|iOS)/i.test(navigator.userAgent)) {

//alert(navigator.userAgent);

window.location.href ="iPhone.html";

} else if (/(Android)/i.test(navigator.userAgent)) {

//alert(navigator.userAgent);

window.location.href ="Android.html";

} else {

window.location.href ="pc.html";

};

也可以通过这样来适配，然后直接转跳到移动端页面：

function mobile_device_detect(url){
  var thisOS=navigator.platform;
  var os=new Array("iPhone","iPod","iPad","android","Nokia","SymbianOS","Symbian","Windows Phone","Phone","Linux armv71","MAUI","UNTRUSTED/1.0","Windows CE","BlackBerry","IEMobile");
  for(var i=0;i<os.length;i++){
    if(thisOS.match(os[i])){
      window.location.href=url;
    }
  }
  if(navigator.platform.indexOf('iPad') != -1){
    window.location.href=url;
  }
  var check = navigator.appVersion;
  if( check.match(/linux/i) ){
    if(check.match(/mobile/i) || check.match(/X11/i)){
      window.location.href=url;
    }
  }
}

function mobile_device_detect(url){

var thisOS=navigator.platform;

var os=new Array("iPhone","iPod","iPad","android","Nokia","SymbianOS","Symbian","Windows Phone","Phone","Linux armv71","MAUI","UNTRUSTED/1.0","Windows CE","BlackBerry","IEMobile");

for(var i=0;i<os.length;i++){

if(thisOS.match(os[i])){

window.location.href=url;

}

if(navigator.platform.indexOf('iPad') != -1){

window.location.href=url;

}

var check = navigator.appVersion;

if( check.match(/linux/i) ){

if(check.match(/mobile/i) || check.match(/X11/i)){

window.location.href=url;

}

参考链接

判断网页是通过PC端还是移动终端打开的

CSS高度自适应铺满全屏

HTML:

<!DOCTYPE html>
<html>
 
<head>
    <meta charset="utf-8" />
    <title>dddd</title>
    <link rel="stylesheet" type="text/css" href="test.css" />
</head>
 
<body class="HolyGrail">
    <header>...</header>
    <div class="HolyGrail-body ">
        <main class="HolyGrail-content">...</main>
        <nav class="HolyGrail-nav">...</nav>
        <aside class="HolyGrail-ads">...</aside>
    </div>
    <footer>...</footer>
</body>

<!DOCTYPE html>

<html>

<head>

</head>

</div>

</body>

CSS:

.HolyGrail {
    display: flex;
    flex-direction: column;
    background-color: blueviolet;
}
 
header,
footer {
    height: 100px;
    background-color: aquamarine;
}
 
body {
    padding: 0;
    margin: 0;
    min-height: 100vh;
}
 
.HolyGrail-body {
    flex: 1;
    background-color: brown;
}

.HolyGrail {

display: flex;

flex-direction: column;

background-color: blueviolet;

}

header,

footer {

height: 100px;

background-color: aquamarine;

}

body {

padding: 0;

margin: 0;

min-height: 100vh;

}

.HolyGrail-body {

flex: 1;

background-color: brown;

}

这里需要注意的是设置body的min-height: 100vh;以及margin: 0;

vw和vh

vm、vh、vmin、vmax是一种视窗单位，也是相对单位。它相对的不是父节点或者页面的根节点。而是由视窗（Viewport）大小来决定的，单位 1，代表类似于 1%。视窗(Viewport)是你的浏览器实际显示内容的区域—，换句话说是你的不包括工具栏和按钮的网页浏览器。

具体描述如下：

vw：视窗宽度的百分比（1vw 代表视窗的宽度为 1%）
vh：视窗高度的百分比
vmin：取当前Vw和Vh中较小的那一个值
vmax：取当前Vw和Vh中较大的那一个值

vh和vw相对于视口的高度和宽度， 1vh 等于1/100的视口高度，1vw 等于1/100的视口宽度比如：浏览器高度900px，宽度为750px, 1 vh = 900px/100 = 9 px，1vw = 750px/100 = 7.5 px，很容易实现与同屏幕等高的框。

参考链接

spring boot设置favicon，favicon不生效，不成功，不起作用

Favicon配置

默认的Favicon图标

关闭默认图标
在application.properties中添加：

spring.mvc.favicon.enabled=false

1	spring.mvc.favicon.enabled=false

或者（我这个有效果）：

spring.favicon.enabled = false

1	spring.favicon.enabled = false

效果具体原因：https://jira.spring.io/browse/SPR-12851

spring boot设置favicon，favicon不生效，不成功，不起作用

springboot显示的是一片叶子，我们如何使用自己的favicon呢？

1.将favicon.icon放到resources目录下例如：/public,/static等等

2.完成上面的步骤还不能显示，还需在你的页面的head标签添加代码

<head>
    <meta charset="UTF-8">
    <title>登录</title>
    <link rel="shortcut icon" th:href="@{/favicon.ico}" type="image/x-icon"/>
    <link rel="icon" th:href="@{/favicon.ico}" type="image/x-icon"/>
    <link rel="bookmark" th:href="@{/favicon.ico}" type="image/x-icon"/>
</head>

<head>

</head>

3.注意我使用的thymeleaf所以是以上代码片段如果你不是请这样添加

<head>
    <meta charset="UTF-8">
    <title>登录</title>
    <link href="/favicon.ico" rel="shortcut icon" type="image/x-icon"/>
    <link href="/favicon.ico" rel="icon" type="image/x-icon"/>
    <link href="/favicon.ico" rel="bookmark" type="image/x-icon"/>
</head>

<head>

</head>

参考链接

spring boot设置favicon，favicon不生效，不成功，不起作用

fail2ban with OpenVPN(ubuntu 20.04)

This page describes how to set up fail2ban with OpenVPN 2.4.7 (tested on ubuntu 20.04)

Create /etc/fail2ban/filter.d/openvpn.conf containing:

# Fail2Ban filter for selected OpenVPN rejections
#
#

[Definition]

# Example messages (other matched messages not seen in the testing server's logs):
# Fri Sep 23 11:55:36 2016 TLS Error: incoming packet authentication failed from [AF_INET]59.90.146.160:51223
# Thu Aug 25 09:36:02 2016 117.207.115.143:58922 TLS Error: TLS handshake failed

failregex = ^ TLS Error: incoming packet authentication failed from \[AF_INET\]<HOST>:\d+$
            ^ <HOST>:\d+ Connection reset, restarting
            ^ <HOST>:\d+ TLS Auth Error
            ^ <HOST>:\d+ TLS Error: TLS handshake failed$
            ^ <HOST>:\d+ VERIFY ERROR

ignoreregex =

# Fail2Ban filter for selected OpenVPN rejections

[Definition]

# Example messages (other matched messages not seen in the testing server's logs):

# Fri Sep 23 11:55:36 2016 TLS Error: incoming packet authentication failed from [AF_INET]59.90.146.160:51223

# Thu Aug 25 09:36:02 2016 117.207.115.143:58922 TLS Error: TLS handshake failed

failregex = ^ TLS Error: incoming packet authentication failed from \[AF_INET\]<HOST>:\d+$

^ <HOST>:\d+ Connection reset, restarting

^ <HOST>:\d+ TLS Auth Error

^ <HOST>:\d+ TLS Error: TLS handshake failed$

^ <HOST>:\d+ VERIFY ERROR

ignoreregex =

Create /etc/fail2ban/jail.local containing:

# Fail2Ban configuration fragment for OpenVPN

[openvpn]
enabled  = true
port     = 1194
protocol = udp
filter   = openvpn
logpath  = /var/log/openvpn/openvpn.log
maxretry = 3

# Fail2Ban configuration fragment for OpenVPN

[openvpn]

enabled = true

port = 1194

protocol = udp

filter = openvpn

logpath = /var/log/openvpn/openvpn.log

maxretry = 3

To effect the configuration change:

$ service fail2ban restart

1	$ service fail2ban restart

To test the configuration change, check /var/log/fail2ban.log initially for service start messages and later for WARNING [openvpn] Ban and Unban messages.

参考链接

HOWTO fail2ban with OpenVPN

禁止macOS系统产生.DS_Store文件的方法

Mac经常会产生 .DS_Store 的隐藏文件，虽然在 Mac 上看不到，但是有时用了人家的 U 盘或把 U 盘拿到 Windows 系统上用，就会看到。

.DS_Store 是 Mac OS 保存文件夹的自定义属性的隐藏文件，如文件的图标位置或背景色，相当于Windows 的 desktop.ini。

禁止 .DS_Store 生成：
打开 “终端” ，复制黏贴下面的命令，回车执行，重启Mac即可生效。

$ defaults write com.apple.desktopservices DSDontWriteNetworkStores -bool TRUE

1

$ defaults write com.apple.desktopservices DSDontWriteNetworkStores -bool TRUE
恢复 .DS_Store 生成：

$ defaults delete com.apple.desktopservices DSDontWriteNetworkStores

1

$ defaults delete com.apple.desktopservices DSDontWriteNetworkStores

参考链接

JUnit中对Exception的判断

对于使用验证 Test Case 方法中抛出的异常，我起初想到的是一种比较简单的方法，但是显得比较繁琐：

    @Test
    public void testOldStyle() {
        try {
            double value = Math.random();
            if(value < 0.5) {
                throw new IllegalStateException("test");
            }
            Assert.fail("Expect IllegalStateException");
        } catch(IllegalStateException e) {
        }
    }

@Test

public void testOldStyle() {

try {

double value = Math.random();

if(value < 0.5) {

throw new IllegalStateException("test");

}

Assert.fail("Expect IllegalStateException");

} catch(IllegalStateException e) {

}

Google了一下，找到另外几种更加方便的方法：１，使用Test注解中的expected字段判断抛出异常的类型。2，使用ExpectedException的Rule注解。
个人偏好用Test注解中的expected字段，它先的更加简洁，不管读起来还是写起来都很方便，并且一目了然：

    @Test(expected = IllegalStateException.class)
    public void testThrowException() {
        throw new IllegalStateException("test");
    }
    
    @Test(expected = IllegalStateException.class)
    public void testNotThrowException() {
        System.out.println("No Exception throws");
    }

@Test(expected = IllegalStateException.class)

public void testThrowException() {

throw new IllegalStateException("test");

}

@Test(expected = IllegalStateException.class)

public void testNotThrowException() {

System.out.println("No Exception throws");

}

对Rule注解的使用（只有在JUnit4.7以后才有这个功能），它提供了更加强大的功能，它可以同时检查异常类型以及异常消息内容，这些内容可以只包含其中的某些字符，ExpectedException还支持使用hamcrest中的Matcher，默认使用IsInstanceOf和StringContains Matcher。在BlockJUnit4ClassRunner的实现中，每一个Test Case运行时都会重新创建Test Class的实例，因而在使用ExpectedException这个Rule时，不用担心在多个Test Case之间相互影响的问题：

    @Rule
    public final ExpectedException expectedException = ExpectedException.none();
    
    @Test
    public void testThrowExceptionWithRule() {
        expectedException.expect(IllegalStateException.class);
        
        throw new IllegalStateException("test");
    }
    
    @Test
    public void testThrowExceptionAndMessageWithRule() {
        expectedException.expect(IllegalStateException.class);
        expectedException.expectMessage("fail");
        
        throw new IllegalStateException("expect fail");
    }

@Rule

public final ExpectedException expectedException = ExpectedException.none();

@Test

public void testThrowExceptionWithRule() {

expectedException.expect(IllegalStateException.class);

throw new IllegalStateException("test");

}

@Test

public void testThrowExceptionAndMessageWithRule() {

expectedException.expect(IllegalStateException.class);

expectedException.expectMessage("fail");

throw new IllegalStateException("expect fail");

}

在stackoverflow中还有人提到了使用google-code中的catch-exception工程，今天没时间看了，回去好好研究一下。

地址是：http://code.google.com/p/catch-exception/

参考链接

JUnit中对Exception的判断

PBKDF2加密的实现

PBKDF2(Password-Based Key Derivation Function)

通过哈希算法进行加密。由于哈希算法是单向的，能够将不论什么大小的数据转化为定长的“指纹”，并且无法被反向计算。

另外，即使数据源仅仅修改了一丁点。哈希的结果也会全然不同。

这种特性使得它很适合用于保存password。由于我们须要加密后的password无法被解密，同一时候也能保证正确校验每一个用户的password。可是哈希加密能够通过字典攻击和暴力攻击破解。

password加盐。盐是一个加入到用户的password哈希过程中的一段随机序列。

这个机制可以防止通过预先计算结果的彩虹表破解。每一个用户都有自己的盐，这种结果就是即使用户的password同样。通过加盐后哈希值也将不同。

为了校验password是否正确，我们须要储存盐值。通常和password哈希值一起存放在账户数据库中。或者直接存为哈希字符串的一部分。

import java.math.BigInteger;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.KeySpec;

import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;

public class PasswordEncryption {

    public static final String PBKDF2_ALGORITHM = "PBKDF2WithHmacSHA1";

    /**
     * 盐的长度
     */
    public static final int SALT_BYTE_SIZE = 32 / 2;

    /**
     * 生成密文的长度
     */
    public static final int HASH_BIT_SIZE = 128 * 4;

    /**
     * 迭代次数
     */
    public static final int PBKDF2_ITERATIONS = 1000;

    /**
     * 对输入的password进行验证
     *
     * @param attemptedPassword 待验证的password
     * @param encryptedPassword 密文
     * @param salt              盐值
     * @return 是否验证成功
     * @throws NoSuchAlgorithmException
     * @throws InvalidKeySpecException
     */
    public static boolean authenticate(String attemptedPassword, String encryptedPassword, String salt)
            throws NoSuchAlgorithmException, InvalidKeySpecException {
        // 用同样的盐值对用户输入的password进行加密
        String encryptedAttemptedPassword = getEncryptedPassword(attemptedPassword, salt);
        // 把加密后的密文和原密文进行比較，同样则验证成功。否则失败
        return encryptedAttemptedPassword.equals(encryptedPassword);
    }

    /**
     * 生成密文
     *
     * @param password 明文password
     * @param salt     盐值
     * @return
     * @throws NoSuchAlgorithmException
     * @throws InvalidKeySpecException
     */
    public static String getEncryptedPassword(String password, String salt) throws NoSuchAlgorithmException,
            InvalidKeySpecException {

        KeySpec spec = new PBEKeySpec(password.toCharArray(), fromHex(salt), PBKDF2_ITERATIONS, HASH_BIT_SIZE);
        SecretKeyFactory f = SecretKeyFactory.getInstance(PBKDF2_ALGORITHM);
        return toHex(f.generateSecret(spec).getEncoded());
    }

    /**
     * 通过提供加密的强随机数生成器 生成盐
     *
     * @return
     * @throws NoSuchAlgorithmException
     */
    public static String generateSalt() throws NoSuchAlgorithmException {
        SecureRandom random = SecureRandom.getInstance("SHA1PRNG");
        byte[] salt = new byte[SALT_BYTE_SIZE];
        random.nextBytes(salt);

        return toHex(salt);
    }

    /**
     * 十六进制字符串转二进制字符串
     *
     * @param hex the hex string
     * @return the hex string decoded into a byte array
     */
    private static byte[] fromHex(String hex) {
        byte[] binary = new byte[hex.length() / 2];
        for (int i = 0; i < binary.length; i++) {
            binary[i] = (byte) Integer.parseInt(hex.substring(2 * i, 2 * i + 2), 16);
        }
        return binary;
    }

    /**
     * 二进制字符串转十六进制字符串
     *
     * @param array the byte array to convert
     * @return a length*2 character string encoding the byte array
     */
    private static String toHex(byte[] array) {
        BigInteger bi = new BigInteger(1, array);
        String hex = bi.toString(16);
        int paddingLength = (array.length * 2) - hex.length();
        if (paddingLength > 0)
            return String.format("%0" + paddingLength + "d", 0) + hex;
        else
            return hex;
    }
}

100

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import java.math.BigInteger;

import java.security.NoSuchAlgorithmException;

import java.security.SecureRandom;

import java.security.spec.InvalidKeySpecException;

import java.security.spec.KeySpec;

import javax.crypto.SecretKeyFactory;

import javax.crypto.spec.PBEKeySpec;

public class PasswordEncryption {

public static final String PBKDF2_ALGORITHM = "PBKDF2WithHmacSHA1";

/**

* 盐的长度

public static final int SALT_BYTE_SIZE = 32 / 2;

/**

* 生成密文的长度

public static final int HASH_BIT_SIZE = 128 * 4;

/**

* 迭代次数

public static final int PBKDF2_ITERATIONS = 1000;

/**

* 对输入的password进行验证

* @param attemptedPassword 待验证的password

* @param encryptedPassword 密文

* @param salt 盐值

* @return 是否验证成功

* @throws NoSuchAlgorithmException

* @throws InvalidKeySpecException

public static boolean authenticate(String attemptedPassword, String encryptedPassword, String salt)

throws NoSuchAlgorithmException, InvalidKeySpecException {

// 用同样的盐值对用户输入的password进行加密

String encryptedAttemptedPassword = getEncryptedPassword(attemptedPassword, salt);

// 把加密后的密文和原密文进行比較，同样则验证成功。否则失败

return encryptedAttemptedPassword.equals(encryptedPassword);

}

/**

* 生成密文

* @param password 明文password

* @param salt 盐值

* @return

* @throws NoSuchAlgorithmException

* @throws InvalidKeySpecException

public static String getEncryptedPassword(String password, String salt) throws NoSuchAlgorithmException,

InvalidKeySpecException {

KeySpec spec = new PBEKeySpec(password.toCharArray(), fromHex(salt), PBKDF2_ITERATIONS, HASH_BIT_SIZE);

SecretKeyFactory f = SecretKeyFactory.getInstance(PBKDF2_ALGORITHM);

return toHex(f.generateSecret(spec).getEncoded());

}

/**

* 通过提供加密的强随机数生成器生成盐

* @return

* @throws NoSuchAlgorithmException

public static String generateSalt() throws NoSuchAlgorithmException {

SecureRandom random = SecureRandom.getInstance("SHA1PRNG");

byte[] salt = new byte[SALT_BYTE_SIZE];

random.nextBytes(salt);

return toHex(salt);

}

/**

* 十六进制字符串转二进制字符串

* @param hex the hex string

* @return the hex string decoded into a byte array

private static byte[] fromHex(String hex) {

byte[] binary = new byte[hex.length() / 2];

for (int i = 0; i < binary.length; i++) {

binary[i] = (byte) Integer.parseInt(hex.substring(2 * i, 2 * i + 2), 16);

}

return binary;

}

/**

* 二进制字符串转十六进制字符串

* @param array the byte array to convert

* @return a length*2 character string encoding the byte array

private static String toHex(byte[] array) {

BigInteger bi = new BigInteger(1, array);

String hex = bi.toString(16);

int paddingLength = (array.length * 2) - hex.length();

if (paddingLength > 0)

return String.format("%0" + paddingLength + "d", 0) + hex;

else

return hex;

}

首先要生成一个盐值salt，再把原始password和salt加密得到密文。验证的时候，把用户输入的password和同样的盐值salt使用同样的加密算法得到一个密文，将这个密文和原密文相比較，同样则验证通过，反之则不通过。

public static void main(String[] args) {
    String password = "test";
    String salt;
    String ciphertext;
    try {
        salt = PasswordEncryption.generateSalt();
        ciphertext = PasswordEncryption.getEncryptedPassword(password, salt);
        boolean result = PasswordEncryption.authenticate(password, ciphertext, salt);

        System.out.println(password + "  " + password.length());
        System.out.println(salt + "  " + salt.length());
        System.out.println(ciphertext + "  " + ciphertext.length());
        if (result) {
            System.out.println("succeed");
        } else {
            System.out.println("failed");
        }
    } catch (NoSuchAlgorithmException e) {
        System.out.println("NoSuchAlgorithmException");
    } catch (InvalidKeySpecException e) {
        System.out.println("InvalidKeySpecException");
    }
}

public static void main(String[] args) {

String password = "test";

String salt;

String ciphertext;

try {

salt = PasswordEncryption.generateSalt();

ciphertext = PasswordEncryption.getEncryptedPassword(password, salt);

boolean result = PasswordEncryption.authenticate(password, ciphertext, salt);

System.out.println(password + " " + password.length());

System.out.println(salt + " " + salt.length());

System.out.println(ciphertext + " " + ciphertext.length());

if (result) {

System.out.println("succeed");

} else {

System.out.println("failed");

}

} catch (NoSuchAlgorithmException e) {

System.out.println("NoSuchAlgorithmException");

} catch (InvalidKeySpecException e) {

System.out.println("InvalidKeySpecException");

}

測试结果为：

test  4
3aca9ca3fa80158b765ece7d0a45f2e8  32
592cb30e95efc720c5accf425ed5f2fe46aa332d9980e6daa234797de49cda731c2c18e667b4dd71ba33797a3dcddd312ff9b03d802bf1cc09aacb2a176cf741  128
succeed

test 4

3aca9ca3fa80158b765ece7d0a45f2e8 32

592cb30e95efc720c5accf425ed5f2fe46aa332d9980e6daa234797de49cda731c2c18e667b4dd71ba33797a3dcddd312ff9b03d802bf1cc09aacb2a176cf741 128

succeed

参考链接

snapd进程持续写盘导致系统卡顿

系统使用一段时间后，莫名其妙出现卡顿现象。发现硬盘灯闪个不停。

经查，是snapd进程持续不停的往硬盘写入数据，同时也会占用CPU。

写入量不大，但是磁盘占用率出奇的高。

导致系统出现卡顿，这个问题从ubuntu18.04到20.04实测都有，更老的版本没有实测不妄加批评。

解决办法网上找了N圈也没有找到解决办法。所以，只好……

干掉它！

$ sudo apt purge snapd

1	$ sudo apt purge snapd

卸载后系统丝般顺滑。。

因为我暂时snap用的不多，加上也没别的办法，毕竟已经影响到系统的正常使用了，只好选择卸载。

有人说不能卸载，可以试试下面的命令：

$ sudo apt autoremove --purge snapd

1	$ sudo apt autoremove --purge snapd

卸载之后，继续重装一下，貌似也不再出现问题。

参考链接

Error 'Character set '#255' is not a compiled ch aracter set and is not specified in the '/usr/local/mariadb10/share/mysql/charse ts/Index.xml' file' on query. Default database: 'wordpress'. Query: 'BEGIN'

以前通过家里ADSL上网无固定外网IP的群晖NAS安全实现与公网MySQL服务器主从同步配置之后，群晖自带的 MariaDB 10.3.21 可以非常流畅的与服务器上的 MySQL 7.x 版本进行主从同步。

前两天系统从 ubuntu 18.04 升级到 ubuntu 20.04 (MySQL 8.x)之后，发现已经无法进行主从同步。

报告如下错误：

$ mysql -u root -p -e "show slave status\G;"
Enter password:
*************************** 1. row ***************************
                Slave_IO_State:
                   Master_Host: 10.8.0.1
                   Master_User: repl1
                   Master_Port: 3306
                 Connect_Retry: 60
               Master_Log_File: mysql-bin.001242
           Read_Master_Log_Pos: 8350259
                Relay_Log_File: mysqld10-relay-bin.000510
                 Relay_Log_Pos: 424
         Relay_Master_Log_File: mysql-bin.001222
              Slave_IO_Running: No
             Slave_SQL_Running: No
               Replicate_Do_DB:
           Replicate_Ignore_DB:
            Replicate_Do_Table:
        Replicate_Ignore_Table:
       Replicate_Wild_Do_Table:
   Replicate_Wild_Ignore_Table:
                    Last_Errno: 22
                    Last_Error: Error 'Character set '#255' is not a compiled character set and is not specified in the '/usr/local/mariadb10/share/mysql/charsets/Index.xml' file' on query. Default database: 'wordpress'. Query: 'BEGIN'
                  Skip_Counter: 0
           Exec_Master_Log_Pos: 125
               Relay_Log_Space: 137841279
               Until_Condition: None
                Until_Log_File:
                 Until_Log_Pos: 0
            Master_SSL_Allowed: Yes
            Master_SSL_CA_File: /var/packages/MariaDB10/etc/ssl/ca.pem
            Master_SSL_CA_Path: /var/packages/MariaDB10/etc/ssl
               Master_SSL_Cert: /var/packages/MariaDB10/etc/ssl/client-cert.pem
             Master_SSL_Cipher:
                Master_SSL_Key: /var/packages/MariaDB10/etc/ssl/client-key.pem
         Seconds_Behind_Master: NULL
 Master_SSL_Verify_Server_Cert: No
                 Last_IO_Errno: 0
                 Last_IO_Error:
                Last_SQL_Errno: 22
                Last_SQL_Error: Error 'Character set '#255' is not a compiled character set and is not specified in the '/usr/local/mariadb10/share/mysql/charsets/Index.xml' file' on query. Default database: 'wordpress'. Query: 'BEGIN'
   Replicate_Ignore_Server_Ids:
              Master_Server_Id: 1
                Master_SSL_Crl: /var/packages/MariaDB10/etc/ssl/ca.pem
            Master_SSL_Crlpath: /var/packages/MariaDB10/etc/ssl
                    Using_Gtid: No
                   Gtid_IO_Pos:
       Replicate_Do_Domain_Ids:
   Replicate_Ignore_Domain_Ids:
                 Parallel_Mode: conservative
                     SQL_Delay: 0
           SQL_Remaining_Delay: NULL
       Slave_SQL_Running_State:
              Slave_DDL_Groups: 0
Slave_Non_Transactional_Groups: 0
    Slave_Transactional_Groups: 0

$ mysql -u root -p -e "show slave status\G;"

Enter password:

*************************** 1. row ***************************

Slave_IO_State:

Master_Host: 10.8.0.1

Master_User: repl1

Master_Port: 3306

Connect_Retry: 60

Master_Log_File: mysql-bin.001242

Read_Master_Log_Pos: 8350259

Relay_Log_File: mysqld10-relay-bin.000510

Relay_Log_Pos: 424

Relay_Master_Log_File: mysql-bin.001222

Slave_IO_Running: No

Slave_SQL_Running: No

Replicate_Do_DB:

Replicate_Ignore_DB:

Replicate_Do_Table:

Replicate_Ignore_Table:

Replicate_Wild_Do_Table:

Replicate_Wild_Ignore_Table:

Last_Errno: 22

Last_Error: Error 'Character set '#255' is not a compiled character set and is not specified in the '/usr/local/mariadb10/share/mysql/charsets/Index.xml' file' on query. Default database: 'wordpress'. Query: 'BEGIN'

Skip_Counter: 0

Exec_Master_Log_Pos: 125

Relay_Log_Space: 137841279

Until_Condition: None

Until_Log_File:

Until_Log_Pos: 0

Master_SSL_Allowed: Yes

Master_SSL_CA_File: /var/packages/MariaDB10/etc/ssl/ca.pem

Master_SSL_CA_Path: /var/packages/MariaDB10/etc/ssl

Master_SSL_Cert: /var/packages/MariaDB10/etc/ssl/client-cert.pem

Master_SSL_Cipher:

Master_SSL_Key: /var/packages/MariaDB10/etc/ssl/client-key.pem

Seconds_Behind_Master: NULL

Master_SSL_Verify_Server_Cert: No

Last_IO_Errno: 0

Last_IO_Error:

Last_SQL_Errno: 22

Last_SQL_Error: Error 'Character set '#255' is not a compiled character set and is not specified in the '/usr/local/mariadb10/share/mysql/charsets/Index.xml' file' on query. Default database: 'wordpress'. Query: 'BEGIN'

Replicate_Ignore_Server_Ids:

Master_Server_Id: 1

Master_SSL_Crl: /var/packages/MariaDB10/etc/ssl/ca.pem

Master_SSL_Crlpath: /var/packages/MariaDB10/etc/ssl

Using_Gtid: No

Gtid_IO_Pos:

Replicate_Do_Domain_Ids:

Replicate_Ignore_Domain_Ids:

Parallel_Mode: conservative

SQL_Delay: 0

SQL_Remaining_Delay: NULL

Slave_SQL_Running_State:

Slave_DDL_Groups: 0

Slave_Non_Transactional_Groups: 0

Slave_Transactional_Groups: 0

网上查询很久，找到原因 MySQL 8.016 master with MariaDB 10.2 slave on AWS RDS, Character set '#255' is not a compiled character set

This could be a serious problem when replicating between MySQL 8.0 and MariaDB 10.x.

The default (for good technical reasons) COLLATION for the 8.0 is utf8mb4_0900_ai_ci. Note the "255" associated with it. MariaDB has not yet adopted the Unicode 9.0 collations.

Furthermore, Oracle (MySQL 8.0) did a major rewrite of the collation code, thereby possibly making collation tables incompatible.

A probable fix is to switch to the next best general-purpose collation, utf8mb4_unicode_520_ci (246) (based on Unicode 5.20). This would require ALTERing all the columns' collations. ALTER TABLE .. CONVERT TO .. might be the fastest way. Those could be generated via a SELECT .. information_schema.tables ....

大致原因就是MySql 8.0默认使用了最新的utf8mb4_0900_ai_ci字符集，然而MariaDB 10.3.x版本不支持这个字符集，导致无法同步。

8.0.17:

mysql> show collation like 'utf8mb4%';
+----------------------------+---------+-----+---------+----------+---------+---------------+
| Collation                  | Charset | Id  | Default | Compiled | Sortlen | Pad_attribute |
+----------------------------+---------+-----+---------+----------+---------+---------------+
| utf8mb4_0900_ai_ci         | utf8mb4 | 255 | Yes     | Yes      |       0 | NO PAD        |
| utf8mb4_0900_as_ci         | utf8mb4 | 305 |         | Yes      |       0 | NO PAD        |
| utf8mb4_0900_as_cs         | utf8mb4 | 278 |         | Yes      |       0 | NO PAD        |
| utf8mb4_0900_bin           | utf8mb4 | 309 |         | Yes      |       1 | NO PAD        |
| utf8mb4_bin                | utf8mb4 |  46 |         | Yes      |       1 | PAD SPACE     |
| utf8mb4_croatian_ci        | utf8mb4 | 245 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_cs_0900_ai_ci      | utf8mb4 | 266 |         | Yes      |       0 | NO PAD        |
| utf8mb4_cs_0900_as_cs      | utf8mb4 | 289 |         | Yes      |       0 | NO PAD        |
| utf8mb4_czech_ci           | utf8mb4 | 234 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_danish_ci          | utf8mb4 | 235 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_da_0900_ai_ci      | utf8mb4 | 267 |         | Yes      |       0 | NO PAD        |
| utf8mb4_da_0900_as_cs      | utf8mb4 | 290 |         | Yes      |       0 | NO PAD        |
| utf8mb4_de_pb_0900_ai_ci   | utf8mb4 | 256 |         | Yes      |       0 | NO PAD        |
| utf8mb4_de_pb_0900_as_cs   | utf8mb4 | 279 |         | Yes      |       0 | NO PAD        |
| utf8mb4_eo_0900_ai_ci      | utf8mb4 | 273 |         | Yes      |       0 | NO PAD        |
| utf8mb4_eo_0900_as_cs      | utf8mb4 | 296 |         | Yes      |       0 | NO PAD        |
| utf8mb4_esperanto_ci       | utf8mb4 | 241 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_estonian_ci        | utf8mb4 | 230 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_es_0900_ai_ci      | utf8mb4 | 263 |         | Yes      |       0 | NO PAD        |
| utf8mb4_es_0900_as_cs      | utf8mb4 | 286 |         | Yes      |       0 | NO PAD        |
| utf8mb4_es_trad_0900_ai_ci | utf8mb4 | 270 |         | Yes      |       0 | NO PAD        |
| utf8mb4_es_trad_0900_as_cs | utf8mb4 | 293 |         | Yes      |       0 | NO PAD        |
| utf8mb4_et_0900_ai_ci      | utf8mb4 | 262 |         | Yes      |       0 | NO PAD        |
| utf8mb4_et_0900_as_cs      | utf8mb4 | 285 |         | Yes      |       0 | NO PAD        |
| utf8mb4_general_ci         | utf8mb4 |  45 |         | Yes      |       1 | PAD SPACE     |
| utf8mb4_german2_ci         | utf8mb4 | 244 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_hr_0900_ai_ci      | utf8mb4 | 275 |         | Yes      |       0 | NO PAD        |
| utf8mb4_hr_0900_as_cs      | utf8mb4 | 298 |         | Yes      |       0 | NO PAD        |
| utf8mb4_hungarian_ci       | utf8mb4 | 242 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_hu_0900_ai_ci      | utf8mb4 | 274 |         | Yes      |       0 | NO PAD        |
| utf8mb4_hu_0900_as_cs      | utf8mb4 | 297 |         | Yes      |       0 | NO PAD        |
| utf8mb4_icelandic_ci       | utf8mb4 | 225 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_is_0900_ai_ci      | utf8mb4 | 257 |         | Yes      |       0 | NO PAD        |
| utf8mb4_is_0900_as_cs      | utf8mb4 | 280 |         | Yes      |       0 | NO PAD        |
| utf8mb4_ja_0900_as_cs      | utf8mb4 | 303 |         | Yes      |       0 | NO PAD        |
| utf8mb4_ja_0900_as_cs_ks   | utf8mb4 | 304 |         | Yes      |      24 | NO PAD        |
| utf8mb4_latvian_ci         | utf8mb4 | 226 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_la_0900_ai_ci      | utf8mb4 | 271 |         | Yes      |       0 | NO PAD        |
| utf8mb4_la_0900_as_cs      | utf8mb4 | 294 |         | Yes      |       0 | NO PAD        |
| utf8mb4_lithuanian_ci      | utf8mb4 | 236 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_lt_0900_ai_ci      | utf8mb4 | 268 |         | Yes      |       0 | NO PAD        |
| utf8mb4_lt_0900_as_cs      | utf8mb4 | 291 |         | Yes      |       0 | NO PAD        |
| utf8mb4_lv_0900_ai_ci      | utf8mb4 | 258 |         | Yes      |       0 | NO PAD        |
| utf8mb4_lv_0900_as_cs      | utf8mb4 | 281 |         | Yes      |       0 | NO PAD        |
| utf8mb4_persian_ci         | utf8mb4 | 240 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_pl_0900_ai_ci      | utf8mb4 | 261 |         | Yes      |       0 | NO PAD        |
| utf8mb4_pl_0900_as_cs      | utf8mb4 | 284 |         | Yes      |       0 | NO PAD        |
| utf8mb4_polish_ci          | utf8mb4 | 229 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_romanian_ci        | utf8mb4 | 227 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_roman_ci           | utf8mb4 | 239 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_ro_0900_ai_ci      | utf8mb4 | 259 |         | Yes      |       0 | NO PAD        |
| utf8mb4_ro_0900_as_cs      | utf8mb4 | 282 |         | Yes      |       0 | NO PAD        |
| utf8mb4_ru_0900_ai_ci      | utf8mb4 | 306 |         | Yes      |       0 | NO PAD        |
| utf8mb4_ru_0900_as_cs      | utf8mb4 | 307 |         | Yes      |       0 | NO PAD        |
| utf8mb4_sinhala_ci         | utf8mb4 | 243 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_sk_0900_ai_ci      | utf8mb4 | 269 |         | Yes      |       0 | NO PAD        |
| utf8mb4_sk_0900_as_cs      | utf8mb4 | 292 |         | Yes      |       0 | NO PAD        |
| utf8mb4_slovak_ci          | utf8mb4 | 237 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_slovenian_ci       | utf8mb4 | 228 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_sl_0900_ai_ci      | utf8mb4 | 260 |         | Yes      |       0 | NO PAD        |
| utf8mb4_sl_0900_as_cs      | utf8mb4 | 283 |         | Yes      |       0 | NO PAD        |
| utf8mb4_spanish2_ci        | utf8mb4 | 238 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_spanish_ci         | utf8mb4 | 231 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_sv_0900_ai_ci      | utf8mb4 | 264 |         | Yes      |       0 | NO PAD        |
| utf8mb4_sv_0900_as_cs      | utf8mb4 | 287 |         | Yes      |       0 | NO PAD        |
| utf8mb4_swedish_ci         | utf8mb4 | 232 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_tr_0900_ai_ci      | utf8mb4 | 265 |         | Yes      |       0 | NO PAD        |
| utf8mb4_tr_0900_as_cs      | utf8mb4 | 288 |         | Yes      |       0 | NO PAD        |
| utf8mb4_turkish_ci         | utf8mb4 | 233 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_unicode_520_ci     | utf8mb4 | 246 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_unicode_ci         | utf8mb4 | 224 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_vietnamese_ci      | utf8mb4 | 247 |         | Yes      |       8 | PAD SPACE     |
| utf8mb4_vi_0900_ai_ci      | utf8mb4 | 277 |         | Yes      |       0 | NO PAD        |
| utf8mb4_vi_0900_as_cs      | utf8mb4 | 300 |         | Yes      |       0 | NO PAD        |
| utf8mb4_zh_0900_as_cs      | utf8mb4 | 308 |         | Yes      |       0 | NO PAD        |
+----------------------------+---------+-----+---------+----------+---------+---------------+
75 rows in set (0.01 sec)

mysql> show collation like 'utf8mb4%';

+----------------------------+---------+-----+---------+----------+---------+---------------+

+----------------------------+---------+-----+---------+----------+---------+---------------+

| utf8mb4_0900_ai_ci | utf8mb4 | 255 | Yes | Yes | 0 | NO PAD |

| utf8mb4_0900_as_ci | utf8mb4 | 305 | | Yes | 0 | NO PAD |

| utf8mb4_0900_as_cs | utf8mb4 | 278 | | Yes | 0 | NO PAD |

| utf8mb4_0900_bin | utf8mb4 | 309 | | Yes | 1 | NO PAD |

| utf8mb4_bin | utf8mb4 | 46 | | Yes | 1 | PAD SPACE |

| utf8mb4_croatian_ci | utf8mb4 | 245 | | Yes | 8 | PAD SPACE |

| utf8mb4_cs_0900_ai_ci | utf8mb4 | 266 | | Yes | 0 | NO PAD |

| utf8mb4_cs_0900_as_cs | utf8mb4 | 289 | | Yes | 0 | NO PAD |

| utf8mb4_czech_ci | utf8mb4 | 234 | | Yes | 8 | PAD SPACE |

| utf8mb4_danish_ci | utf8mb4 | 235 | | Yes | 8 | PAD SPACE |

| utf8mb4_da_0900_ai_ci | utf8mb4 | 267 | | Yes | 0 | NO PAD |

| utf8mb4_da_0900_as_cs | utf8mb4 | 290 | | Yes | 0 | NO PAD |

| utf8mb4_de_pb_0900_ai_ci | utf8mb4 | 256 | | Yes | 0 | NO PAD |

| utf8mb4_de_pb_0900_as_cs | utf8mb4 | 279 | | Yes | 0 | NO PAD |

| utf8mb4_eo_0900_ai_ci | utf8mb4 | 273 | | Yes | 0 | NO PAD |

| utf8mb4_eo_0900_as_cs | utf8mb4 | 296 | | Yes | 0 | NO PAD |

| utf8mb4_esperanto_ci | utf8mb4 | 241 | | Yes | 8 | PAD SPACE |

| utf8mb4_estonian_ci | utf8mb4 | 230 | | Yes | 8 | PAD SPACE |

| utf8mb4_es_0900_ai_ci | utf8mb4 | 263 | | Yes | 0 | NO PAD |

| utf8mb4_es_0900_as_cs | utf8mb4 | 286 | | Yes | 0 | NO PAD |

| utf8mb4_es_trad_0900_ai_ci | utf8mb4 | 270 | | Yes | 0 | NO PAD |

| utf8mb4_es_trad_0900_as_cs | utf8mb4 | 293 | | Yes | 0 | NO PAD |

| utf8mb4_et_0900_ai_ci | utf8mb4 | 262 | | Yes | 0 | NO PAD |

| utf8mb4_et_0900_as_cs | utf8mb4 | 285 | | Yes | 0 | NO PAD |

| utf8mb4_general_ci | utf8mb4 | 45 | | Yes | 1 | PAD SPACE |

| utf8mb4_german2_ci | utf8mb4 | 244 | | Yes | 8 | PAD SPACE |

| utf8mb4_hr_0900_ai_ci | utf8mb4 | 275 | | Yes | 0 | NO PAD |

| utf8mb4_hr_0900_as_cs | utf8mb4 | 298 | | Yes | 0 | NO PAD |

| utf8mb4_hungarian_ci | utf8mb4 | 242 | | Yes | 8 | PAD SPACE |

| utf8mb4_hu_0900_ai_ci | utf8mb4 | 274 | | Yes | 0 | NO PAD |

| utf8mb4_hu_0900_as_cs | utf8mb4 | 297 | | Yes | 0 | NO PAD |

| utf8mb4_icelandic_ci | utf8mb4 | 225 | | Yes | 8 | PAD SPACE |

| utf8mb4_is_0900_ai_ci | utf8mb4 | 257 | | Yes | 0 | NO PAD |

| utf8mb4_is_0900_as_cs | utf8mb4 | 280 | | Yes | 0 | NO PAD |

| utf8mb4_ja_0900_as_cs | utf8mb4 | 303 | | Yes | 0 | NO PAD |

| utf8mb4_ja_0900_as_cs_ks | utf8mb4 | 304 | | Yes | 24 | NO PAD |

| utf8mb4_latvian_ci | utf8mb4 | 226 | | Yes | 8 | PAD SPACE |

| utf8mb4_la_0900_ai_ci | utf8mb4 | 271 | | Yes | 0 | NO PAD |

| utf8mb4_la_0900_as_cs | utf8mb4 | 294 | | Yes | 0 | NO PAD |

| utf8mb4_lithuanian_ci | utf8mb4 | 236 | | Yes | 8 | PAD SPACE |

| utf8mb4_lt_0900_ai_ci | utf8mb4 | 268 | | Yes | 0 | NO PAD |

| utf8mb4_lt_0900_as_cs | utf8mb4 | 291 | | Yes | 0 | NO PAD |

| utf8mb4_lv_0900_ai_ci | utf8mb4 | 258 | | Yes | 0 | NO PAD |

| utf8mb4_lv_0900_as_cs | utf8mb4 | 281 | | Yes | 0 | NO PAD |

| utf8mb4_persian_ci | utf8mb4 | 240 | | Yes | 8 | PAD SPACE |

| utf8mb4_pl_0900_ai_ci | utf8mb4 | 261 | | Yes | 0 | NO PAD |

| utf8mb4_pl_0900_as_cs | utf8mb4 | 284 | | Yes | 0 | NO PAD |

| utf8mb4_polish_ci | utf8mb4 | 229 | | Yes | 8 | PAD SPACE |

| utf8mb4_romanian_ci | utf8mb4 | 227 | | Yes | 8 | PAD SPACE |

| utf8mb4_roman_ci | utf8mb4 | 239 | | Yes | 8 | PAD SPACE |

| utf8mb4_ro_0900_ai_ci | utf8mb4 | 259 | | Yes | 0 | NO PAD |

| utf8mb4_ro_0900_as_cs | utf8mb4 | 282 | | Yes | 0 | NO PAD |

| utf8mb4_ru_0900_ai_ci | utf8mb4 | 306 | | Yes | 0 | NO PAD |

| utf8mb4_ru_0900_as_cs | utf8mb4 | 307 | | Yes | 0 | NO PAD |

| utf8mb4_sinhala_ci | utf8mb4 | 243 | | Yes | 8 | PAD SPACE |

| utf8mb4_sk_0900_ai_ci | utf8mb4 | 269 | | Yes | 0 | NO PAD |

| utf8mb4_sk_0900_as_cs | utf8mb4 | 292 | | Yes | 0 | NO PAD |

| utf8mb4_slovak_ci | utf8mb4 | 237 | | Yes | 8 | PAD SPACE |

| utf8mb4_slovenian_ci | utf8mb4 | 228 | | Yes | 8 | PAD SPACE |

| utf8mb4_sl_0900_ai_ci | utf8mb4 | 260 | | Yes | 0 | NO PAD |

| utf8mb4_sl_0900_as_cs | utf8mb4 | 283 | | Yes | 0 | NO PAD |

| utf8mb4_spanish2_ci | utf8mb4 | 238 | | Yes | 8 | PAD SPACE |

| utf8mb4_spanish_ci | utf8mb4 | 231 | | Yes | 8 | PAD SPACE |

| utf8mb4_sv_0900_ai_ci | utf8mb4 | 264 | | Yes | 0 | NO PAD |

| utf8mb4_sv_0900_as_cs | utf8mb4 | 287 | | Yes | 0 | NO PAD |

| utf8mb4_swedish_ci | utf8mb4 | 232 | | Yes | 8 | PAD SPACE |

| utf8mb4_tr_0900_ai_ci | utf8mb4 | 265 | | Yes | 0 | NO PAD |

| utf8mb4_tr_0900_as_cs | utf8mb4 | 288 | | Yes | 0 | NO PAD |

| utf8mb4_turkish_ci | utf8mb4 | 233 | | Yes | 8 | PAD SPACE |

| utf8mb4_unicode_520_ci | utf8mb4 | 246 | | Yes | 8 | PAD SPACE |

| utf8mb4_unicode_ci | utf8mb4 | 224 | | Yes | 8 | PAD SPACE |

| utf8mb4_vietnamese_ci | utf8mb4 | 247 | | Yes | 8 | PAD SPACE |

| utf8mb4_vi_0900_ai_ci | utf8mb4 | 277 | | Yes | 0 | NO PAD |

| utf8mb4_vi_0900_as_cs | utf8mb4 | 300 | | Yes | 0 | NO PAD |

| utf8mb4_zh_0900_as_cs | utf8mb4 | 308 | | Yes | 0 | NO PAD |

+----------------------------+---------+-----+---------+----------+---------+---------------+

75 rows in set (0.01 sec)

MariaDB 10.2.30:

mysql> SHOW COLLATION LIKE 'utf8mb4%';
+------------------------------+---------+------+---------+----------+---------+
| Collation                    | Charset | Id   | Default | Compiled | Sortlen |
+------------------------------+---------+------+---------+----------+---------+
| utf8mb4_general_ci           | utf8mb4 |   45 | Yes     | Yes      |       1 |
| utf8mb4_bin                  | utf8mb4 |   46 |         | Yes      |       1 |
| utf8mb4_unicode_ci           | utf8mb4 |  224 |         | Yes      |       8 |
| utf8mb4_icelandic_ci         | utf8mb4 |  225 |         | Yes      |       8 |
| utf8mb4_latvian_ci           | utf8mb4 |  226 |         | Yes      |       8 |
| utf8mb4_romanian_ci          | utf8mb4 |  227 |         | Yes      |       8 |
| utf8mb4_slovenian_ci         | utf8mb4 |  228 |         | Yes      |       8 |
| utf8mb4_polish_ci            | utf8mb4 |  229 |         | Yes      |       8 |
| utf8mb4_estonian_ci          | utf8mb4 |  230 |         | Yes      |       8 |
| utf8mb4_spanish_ci           | utf8mb4 |  231 |         | Yes      |       8 |
| utf8mb4_swedish_ci           | utf8mb4 |  232 |         | Yes      |       8 |
| utf8mb4_turkish_ci           | utf8mb4 |  233 |         | Yes      |       8 |
| utf8mb4_czech_ci             | utf8mb4 |  234 |         | Yes      |       8 |
| utf8mb4_danish_ci            | utf8mb4 |  235 |         | Yes      |       8 |
| utf8mb4_lithuanian_ci        | utf8mb4 |  236 |         | Yes      |       8 |
| utf8mb4_slovak_ci            | utf8mb4 |  237 |         | Yes      |       8 |
| utf8mb4_spanish2_ci          | utf8mb4 |  238 |         | Yes      |       8 |
| utf8mb4_roman_ci             | utf8mb4 |  239 |         | Yes      |       8 |
| utf8mb4_persian_ci           | utf8mb4 |  240 |         | Yes      |       8 |
| utf8mb4_esperanto_ci         | utf8mb4 |  241 |         | Yes      |       8 |
| utf8mb4_hungarian_ci         | utf8mb4 |  242 |         | Yes      |       8 |
| utf8mb4_sinhala_ci           | utf8mb4 |  243 |         | Yes      |       8 |
| utf8mb4_german2_ci           | utf8mb4 |  244 |         | Yes      |       8 |
| utf8mb4_croatian_mysql561_ci | utf8mb4 |  245 |         | Yes      |       8 |
| utf8mb4_unicode_520_ci       | utf8mb4 |  246 |         | Yes      |       8 | <--
| utf8mb4_vietnamese_ci        | utf8mb4 |  247 |         | Yes      |       8 |
| utf8mb4_croatian_ci          | utf8mb4 |  608 |         | Yes      |       8 |
| utf8mb4_myanmar_ci           | utf8mb4 |  609 |         | Yes      |       8 |
| utf8mb4_thai_520_w2          | utf8mb4 |  610 |         | Yes      |       4 |
| utf8mb4_general_nopad_ci     | utf8mb4 | 1069 |         | Yes      |       1 |
| utf8mb4_nopad_bin            | utf8mb4 | 1070 |         | Yes      |       1 |
| utf8mb4_unicode_nopad_ci     | utf8mb4 | 1248 |         | Yes      |       8 |
| utf8mb4_unicode_520_nopad_ci | utf8mb4 | 1270 |         | Yes      |       8 |
+------------------------------+---------+------+---------+----------+---------+
33 rows in set (0.00 sec)

mysql> SHOW COLLATION LIKE 'utf8mb4%';

+------------------------------+---------+------+---------+----------+---------+

+------------------------------+---------+------+---------+----------+---------+

| utf8mb4_general_ci | utf8mb4 | 45 | Yes | Yes | 1 |

| utf8mb4_bin | utf8mb4 | 46 | | Yes | 1 |

| utf8mb4_unicode_ci | utf8mb4 | 224 | | Yes | 8 |

| utf8mb4_icelandic_ci | utf8mb4 | 225 | | Yes | 8 |

| utf8mb4_latvian_ci | utf8mb4 | 226 | | Yes | 8 |

| utf8mb4_romanian_ci | utf8mb4 | 227 | | Yes | 8 |

| utf8mb4_slovenian_ci | utf8mb4 | 228 | | Yes | 8 |

| utf8mb4_polish_ci | utf8mb4 | 229 | | Yes | 8 |

| utf8mb4_estonian_ci | utf8mb4 | 230 | | Yes | 8 |

| utf8mb4_spanish_ci | utf8mb4 | 231 | | Yes | 8 |

| utf8mb4_swedish_ci | utf8mb4 | 232 | | Yes | 8 |

| utf8mb4_turkish_ci | utf8mb4 | 233 | | Yes | 8 |

| utf8mb4_czech_ci | utf8mb4 | 234 | | Yes | 8 |

| utf8mb4_danish_ci | utf8mb4 | 235 | | Yes | 8 |

| utf8mb4_lithuanian_ci | utf8mb4 | 236 | | Yes | 8 |

| utf8mb4_slovak_ci | utf8mb4 | 237 | | Yes | 8 |

| utf8mb4_spanish2_ci | utf8mb4 | 238 | | Yes | 8 |

| utf8mb4_roman_ci | utf8mb4 | 239 | | Yes | 8 |

| utf8mb4_persian_ci | utf8mb4 | 240 | | Yes | 8 |

| utf8mb4_esperanto_ci | utf8mb4 | 241 | | Yes | 8 |

| utf8mb4_hungarian_ci | utf8mb4 | 242 | | Yes | 8 |

| utf8mb4_sinhala_ci | utf8mb4 | 243 | | Yes | 8 |

| utf8mb4_german2_ci | utf8mb4 | 244 | | Yes | 8 |

| utf8mb4_croatian_mysql561_ci | utf8mb4 | 245 | | Yes | 8 |

| utf8mb4_unicode_520_ci | utf8mb4 | 246 | | Yes | 8 | <--

| utf8mb4_vietnamese_ci | utf8mb4 | 247 | | Yes | 8 |

| utf8mb4_croatian_ci | utf8mb4 | 608 | | Yes | 8 |

| utf8mb4_myanmar_ci | utf8mb4 | 609 | | Yes | 8 |

| utf8mb4_thai_520_w2 | utf8mb4 | 610 | | Yes | 4 |

| utf8mb4_general_nopad_ci | utf8mb4 | 1069 | | Yes | 1 |

| utf8mb4_nopad_bin | utf8mb4 | 1070 | | Yes | 1 |

| utf8mb4_unicode_nopad_ci | utf8mb4 | 1248 | | Yes | 8 |

| utf8mb4_unicode_520_nopad_ci | utf8mb4 | 1270 | | Yes | 8 |

+------------------------------+---------+------+---------+----------+---------+

33 rows in set (0.00 sec)

目前暂时没打算修改主服务器上的数据库，暂时等 MariaDB 更新吧。

参考链接

笛卡尔乘积

笛卡尔乘积是指在数学中，两个集合X和Y的笛卡尔积（Cartesian product），又称直积，表示为X×Y，第一个对象是X的成员而第二个对象是Y的所有可能有序对的其中一个成员。

假设集合A={a, b}，集合B={0, 1, 2}，则两个集合的笛卡尔积为{(a, 0), (a, 1), (a, 2), (b, 0), (b, 1), (b, 2)}。

矩阵的笛卡尔乘积就是矩阵的直积

讲到笛卡尔乘积，就难免会提到数据库中的 "自然连接(⋈)"。

要求：连接两个表 R ⋈ S
(表中标黄的数据后面会说到)

先看两个表头，发现A C是重复出现的

所以连接后，新表头为

然后把A C这两列单独拎出来，如下

发现有两组相同的，（也就是上面标红的数据）
所以这两个表连接之后只有两条记录。

此时，可以做出下图

这时候从原来的R表、S表中找到对应数据填上

这样表格就完成了。

然后根据上述过程，尝试完成下面的例题：

结果：

我们还可以知道当R和S没有公共属性时，则R⋈S = RXS
（没有公共属性，即每个属性都有它们唯一确定的值。所以RXS就没有需要划去的，也没有相同属性需要整合）

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