Java读写分离实现

1、查看源码

AbstractRoutingDataSource类中有个determineTargetDataSource方法

 protected DataSource determineTargetDataSource() {
        Assert.notNull(this.resolvedDataSources, "DataSource router not initialized");
        Object lookupKey = this.determineCurrentLookupKey();
        DataSource dataSource = (DataSource)this.resolvedDataSources.get(lookupKey);
        if (dataSource == null && (this.lenientFallback || lookupKey == null)) {
            dataSource = this.resolvedDefaultDataSource;
        }

        if (dataSource == null) {
            throw new IllegalStateException("Cannot determine target DataSource for lookup key [" + lookupKey + "]");
        } else {
            return dataSource;
        }
    }

determineTargetDataSource会调用抽象方法determineCurrentLookupKey

@Nullable
    protected abstract Object determineCurrentLookupKey();

2、创建类继承AbstractRoutingDataSource

import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;

public class DynamicDataSource extends AbstractRoutingDataSource{

    @Override
    protected Object determineCurrentLookupKey() {
        return DynamicDataSourceHolder.getDbType();
    }

}

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class DynamicDataSourceHolder {
    private static Logger logger = LoggerFactory.getLogger(DynamicDataSourceHolder.class);
    private static ThreadLocal<String> contextHolder = new ThreadLocal<String>();
    public static final String DB_MASTER = "master";
    public static final String DB_SLAVE = "slave";

    public static String getDbType() {
        String db = contextHolder.get();
        if (db == null) {

            db = DB_MASTER;
        }
        return db;
    }

    /**
     * 设置线程的dbType
     * 
     * @param str
     */
    public static void setDbType(String str) {
        logger.debug("所使用的数据源为：" + str);
        contextHolder.set(str);
    }

    /**
     * 清理连接类型
     */
    public static void clearDBType() {
        contextHolder.remove();
    }

}

3、设置Mybatis拦截器

import java.util.Locale;
import java.util.Properties;
import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.executor.keygen.SelectKeyGenerator;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.SqlCommandType;
import org.apache.ibatis.plugin.Interceptor;
import org.apache.ibatis.plugin.Intercepts;
import org.apache.ibatis.plugin.Invocation;
import org.apache.ibatis.plugin.Plugin;
import org.apache.ibatis.plugin.Signature;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.transaction.support.TransactionSynchronizationManager;

@Intercepts({ @Signature(type = Executor.class, method = "update", args = { MappedStatement.class, Object.class }),
        @Signature(type = Executor.class, method = "query", args = { MappedStatement.class, Object.class,
                RowBounds.class, ResultHandler.class }) })
public class DynamicDataSourceInterceptor implements Interceptor {
    private static Logger logger = LoggerFactory.getLogger(DynamicDataSourceInterceptor.class);
    private static final String REGEX = ".*insert\u0020.*|.*delete\u0020.*|.*update\u0020.*";

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        //判断当前是不是事务
        boolean synchronizationActive = TransactionSynchronizationManager.isActualTransactionActive();
        //获取crud操作的参数
        Object[] objects = invocation.getArgs();
        //获取第一个参数可以知道，具体是crud哪个操作
        MappedStatement ms = (MappedStatement) objects[0];
        String lookupKey = DynamicDataSourceHolder.DB_MASTER;
        if (synchronizationActive != true) {
            // 读方法
            if (ms.getSqlCommandType().equals(SqlCommandType.SELECT)) {
                // selectKey 为自增id查询主键(SELECT LAST_INSERT_ID())方法，使用主库
                if (ms.getId().contains(SelectKeyGenerator.SELECT_KEY_SUFFIX)) {
                    lookupKey = DynamicDataSourceHolder.DB_MASTER;
                } else {
                    //获取第二个参数，即sql
                    BoundSql boundSql = ms.getSqlSource().getBoundSql(objects[1]);
                    String sql = boundSql.getSql().toLowerCase(Locale.CHINA).replaceAll("[\t\n\r]", " ");
                    //查看是不是增删改，若是则用主库，查则用从库
                    if (sql.matches(REGEX)) {
                        lookupKey = DynamicDataSourceHolder.DB_MASTER;
                    } else {
                        lookupKey = DynamicDataSourceHolder.DB_SLAVE;
                    }
                }
            }
        } else {
            //若为事务，一般就是写等操作，用主库
            lookupKey = DynamicDataSourceHolder.DB_MASTER;
        }
        logger.debug("设置方法[{}] use [{}] Strategy, SqlCommanType [{}]..", ms.getId(), lookupKey,
                ms.getSqlCommandType().name());
        //最终决定要哪个数据库
        DynamicDataSourceHolder.setDbType(lookupKey);
        return invocation.proceed();
    }
    //若是Excutor就拦截下来
    @Override
    public Object plugin(Object target) {
        //拦截Executor是因为，Execuror支持一系列增删改查
        if (target instanceof Executor) {
            return Plugin.wrap(target, this);
        } else {
            return target;
        }
    }

    @Override
    public void setProperties(Properties arg0) {
        // TODO Auto-generated method stub

    }

}

4、修改Mybatis-conf.xml文件

5、修改Spring-dao.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context.xsd">
    <!-- 配置整合mybatis过程 -->
    <!-- 1.配置数据库相关参数properties的属性：${url} -->
    <bean class="com.imooc.o2o.util.EncryptPropertyPlaceholderConfigurer">
        <property name="locations">
            <list>
                <value>classpath:jdbc.properties</value>
                <value>classpath:redis.properties</value>
            </list>
        </property>
        <property name="fileEncoding" value="UTF-8" />
    </bean>
    <!-- 2.数据库连接池 -->
    <bean id="abstractDataSource" abstract="true"
        class="com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close">
        <!-- c3p0连接池的私有属性 -->
        <property name="maxPoolSize" value="30" />
        <property name="minPoolSize" value="10" />
        <property name="initialPoolSize" value="10"/> 
        <!-- 关闭连接后不自动commit -->
        <property name="autoCommitOnClose" value="false" />
        <!-- 获取连接超时时间 -->
        <property name="checkoutTimeout" value="10000" />
        <!-- 当获取连接失败重试次数 -->
        <property name="acquireRetryAttempts" value="2" />
    </bean>
    <bean id="master" parent="abstractDataSource">
        <!-- 配置连接池属性 -->
        <property name="driverClass" value="${jdbc.driver}" />
        <property name="jdbcUrl" value="${jdbc.master.url}" />
        <property name="user" value="${jdbc.username}" />
        <property name="password" value="${jdbc.password}" />
    </bean>
    <bean id="slave" parent="abstractDataSource">
        <!-- 配置连接池属性 -->
        <property name="driverClass" value="${jdbc.driver}" />
        <property name="jdbcUrl" value="${jdbc.slave.url}" />
        <property name="user" value="${jdbc.username}" />
        <property name="password" value="${jdbc.password}" />
    </bean>
    <!-- 配置动态数据源，这儿targetDataSources就是路由数据源所对应的名称 -->
    <bean id="dynamicDataSource" class="com.imooc.o2o.dao.split.DynamicDataSource">
        <property name="targetDataSources">
            <map>
                <entry value-ref="master" key="master"></entry>
                <entry value-ref="slave" key="slave"></entry>
            </map>
        </property>
    </bean>
    <bean id="dataSource"
        class="org.springframework.jdbc.datasource.LazyConnectionDataSourceProxy">
        <property name="targetDataSource">
            <ref bean="dynamicDataSource" />
        </property>
    </bean>

    <!-- 3.配置SqlSessionFactory对象 -->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <!-- 注入数据库连接池 -->
        <property name="dataSource" ref="dataSource" />
        <!-- 配置MyBaties全局配置文件:mybatis-config.xml -->
        <property name="configLocation" value="classpath:mybatis-config.xml" />
        <!-- 扫描entity包 使用别名 -->
        <property name="typeAliasesPackage" value="com.imooc.entity" />
        <!-- 扫描sql配置文件:mapper需要的xml文件 -->
        <property name="mapperLocations" value="classpath:mapper/*.xml" />
    </bean>

    <!-- 4.配置扫描Dao接口包，动态实现Dao接口，注入到spring容器中 -->
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <!-- 注入sqlSessionFactory -->
        <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory" />
        <!-- 给出需要扫描Dao接口包 -->
        <property name="basePackage" value="com.imooc.o2o.dao" />
    </bean>
</beans>