0x01： Mycat

下载

wget http://dl.mycat.io/1.6.7.3/20190927161129/Mycat-server-1.6.7.3-release-20190927161129-linux.tar.gz

配置

server.xml，Mycat服务器配置，默认端口8066

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mycat:server SYSTEM "server.dtd">
<mycat:server xmlns:mycat="http://io.mycat/">
<system>
<property name="useSqlStat">0</property>
<property name="useGlobleTableCheck">0</property>
<property name="sequnceHandlerType">2</property>
<property name="handleDistributedTransactions">0</property>
<property name="useoffHeapForMerge">1</property>
<property name="memoryPageSize">1m</property>
<property name="spillsFileBufferSize">1k</property>
<property name="useStreamOutput">0</property>
<property name="systemReserveMemorySize">384m</property>
<property name="useZKSwitch">true</property>
</system>

<!--Mycat用户名-->
<user name="root">
<!--Mycat密码-->
<property name="password">root</property>
<!--Mycat数据库名-->
<property name="schemas">mycat_test</property>
</user>

</mycat:server>

schema.xml，Mycat和MySQL节点映射配置

<?xml version="1.0"?>
<!DOCTYPE mycat:schema SYSTEM "schema.dtd">
<mycat:schema xmlns:mycat="http://io.mycat/">
<!--Mycat数据库名-->
<schema name="mycat_test" checkSQLschema="true" sqlMaxLimit="100">
<!--Mycat表名，节点名称列表-->
<table name="mycat_test_student" dataNode="dn1,dn2"/>
</schema>
<!--Mycat节点名称、节点地址、mysql数据库名-->
<dataNode name="dn1" dataHost="localhost1" database="db01" />
<dataNode name="dn2" dataHost="localhost1" database="db02" />

<!--Mycat节点地址-->
<dataHost name="localhost1" maxCon="1000" minCon="10" balance="0"
writeType="0" dbType="mysql" dbDriver="native" switchType="1" slaveThreshold="100">
<heartbeat>select user()</heartbeat>
<!-- mysql数据库服务器、账户、密码 -->
<writeHost host="hostM1" url="192.168.1.71:3306" user="test"
password="test@1234">
</writeHost>
</dataHost>
</mycat:schema>

0x02：Spring Boot

数据源配置

#mycat连接信息
spring.datasource.url=jdbc:mysql://localhost:8066/mycat_test?serverTimezone=GMT
spring.datasource.username=root
spring.datasource.password=root
spring.datasource.driver-class-name=com.mysql.jdbc.Driver

#MyBatis拦截器配置
mybatis.config-location=classpath:mybatis.xml

Mybatis

mybatis.xml插件配置

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">

<configuration>
<settings>
<!-- 打印查询语句 -->
<setting name="logImpl" value="STDOUT_LOGGING" />
</settings>

<typeAliases>
<typeAlias alias="TestPojo" type="xx.xx.TestPojo"/>
</typeAliases>

<!-- 拦截器插件，改写sql -->
<plugins>
<plugin interceptor="xx.interceptor.MyInterceptor">
</plugin>
</plugins>

</configuration>

拦截器

//拦截StatementHandler的prepare方法
@Intercepts(value = {
@Signature(type = StatementHandler.class,
method = "prepare",
args = {Connection.class,Integer.class})})
public class MyInterceptor implements Interceptor {
// 修改sql，添加前后缀
private static final String preState="/*!mycat:datanode=";
private static final String afterState="*/";

@Override
public Object intercept(Invocation invocation) throws Throwable {
StatementHandler statementHandler=(StatementHandler)invocation.getTarget();
MetaObject metaStatementHandler=SystemMetaObject.forObject(statementHandler);
Object object=null;
//分离代理对象链
while(metaStatementHandler.hasGetter("h")){
object=metaStatementHandler.getValue("h");
metaStatementHandler=SystemMetaObject.forObject(object);
}

//获取sql
String sql=(String)metaStatementHandler.getValue("delegate.boundSql.sql");

//根据会话上下文，获取节点标识
String node=(String) SessionUtil.getSession().getAttribute("AppId");
if(node!=null) {
//重写sql，适配mycat
sql = preState + node + afterState + sql;
}

System.out.println("sql is "+sql);
metaStatementHandler.setValue("delegate.boundSql.sql",sql);
Object result = invocation.proceed();
System.out.println("Invocation.proceed()");
return result;
}

// 返回当前拦截的对象(StatementHandler)的动态代理
// 当拦截对象的方法被执行时, 动态代理中执行拦截器intercept方法.
@Override
public Object plugin(Object target) {
return Plugin.wrap(target, this);
}

@Override
public void setProperties(Properties properties) {
String prop1 = properties.getProperty("prop1");
String prop2 = properties.getProperty("prop2");
System.out.println(prop1 + "------" + prop2);
}
}

总结

以上为关键实现，主要过程如下：

• 搭建 Mycat 服务，设置提供的数据库信息
• 配置Mycat动态映射的两个节点，Mycat根据sql语句中的/*!mycat:datanode=dn1*/进行动态切换数据源后执行sql
• 配置 SpringBoot 的 Mycat 数据源连接
• 配置 Mybatis 的拦截器插件
• 配置 Mybatis 拦截器实现，根据上下文节点，改写 sql

注意

• 生产可采用Mycat集群，集群用ZK管理，以动态实例化数据源