《Dubbo 实现原理与源码解析 —— 精品合集》 《Netty 实现原理与源码解析 —— 精品合集》
《Spring 实现原理与源码解析 —— 精品合集》 《MyBatis 实现原理与源码解析 —— 精品合集》
《Spring MVC 实现原理与源码解析 —— 精品合集》 《数据库实体设计合集》
《Spring Boot 实现原理与源码解析 —— 精品合集》 《Java 面试题 + Java 学习指南》

摘要: 原创出处 jianshu.com/p/2222257f96d3 「蓝汀华韶」欢迎转载,保留摘要,谢谢!


🙂🙂🙂关注**微信公众号:【芋道源码】**有福利:

  1. RocketMQ / MyCAT / Sharding-JDBC 所有源码分析文章列表
  2. RocketMQ / MyCAT / Sharding-JDBC 中文注释源码 GitHub 地址
  3. 您对于源码的疑问每条留言将得到认真回复。甚至不知道如何读源码也可以请教噢
  4. 新的源码解析文章实时收到通知。每周更新一篇左右
  5. 认真的源码交流微信群。

方案1

通过MyBatis配置文件创建读写分离两个DataSource,每个SqlSessionFactoryBean对象的mapperLocations属性制定两个读写数据源的配置文件。将所有读的操作配置在读文件中,所有写的操作配置在写文件中。

  • 优点:实现简单
  • 缺点:维护麻烦,需要对原有的xml文件进行重新修改,不支持多读,不易扩展
  • 实现方式

<bean id="abstractDataSource" abstract="true" class="com.alibaba.druid.pool.DruidDataSource" init-method="init"
destroy-method="close">
<property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
<!-- 配置获取连接等待超时的时间 -->
<property name="maxWait" value="60000"/>
<!-- 配置间隔多久才进行一次检测,检测需要关闭的空闲连接,单位是毫秒 -->
<property name="timeBetweenEvictionRunsMillis" value="60000"/>
<!-- 配置一个连接在池中最小生存的时间,单位是毫秒 -->
<property name="minEvictableIdleTimeMillis" value="300000"/>
<property name="validationQuery" value="SELECT 'x'"/>
<property name="testWhileIdle" value="true"/>
<property name="testOnBorrow" value="false"/>
<property name="testOnReturn" value="false"/>
<!-- 打开PSCache,并且指定每个连接上PSCache的大小 -->
<property name="poolPreparedStatements" value="true"/>
<property name="maxPoolPreparedStatementPerConnectionSize" value="20"/>
<property name="filters" value="config"/>
<property name="connectionProperties" value="config.decrypt=true" />
</bean>

<bean id="readDataSource" parent="abstractDataSource">
<!-- 基本属性 url、user、password -->
<property name="url" value="${read.jdbc.url}"/>
<property name="username" value="${read.jdbc.user}"/>
<property name="password" value="${read.jdbc.password}"/>
<!-- 配置初始化大小、最小、最大 -->
<property name="initialSize" value="${read.jdbc.initPoolSize}"/>
<property name="minIdle" value="10"/>
<property name="maxActive" value="${read.jdbc.maxPoolSize}"/>
</bean>

<bean id="writeDataSource" parent="abstractDataSource">
<!-- 基本属性 url、user、password -->
<property name="url" value="${write.jdbc.url}"/>
<property name="username" value="${write.jdbc.user}"/>
<property name="password" value="${write.jdbc.password}"/>
<!-- 配置初始化大小、最小、最大 -->
<property name="initialSize" value="${write.jdbc.initPoolSize}"/>
<property name="minIdle" value="10"/>
<property name="maxActive" value="${write.jdbc.maxPoolSize}"/>
</bean>

<bean id="readSqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<!-- 实例化sqlSessionFactory时需要使用上述配置好的数据源以及SQL映射文件 -->
<property name="dataSource" ref="readDataSource"/>
<property name="mapperLocations" value="classpath:mapper/read/*.xml"/>
</bean>

<bean id="writeSqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<!-- 实例化sqlSessionFactory时需要使用上述配置好的数据源以及SQL映射文件 -->
<property name="dataSource" ref="writeDataSource"/>
<property name="mapperLocations" value="classpath:mapper/write/*.xml"/>
</bean>

方案2

通过Spring AOP在业务层实现读写分离,在DAO层调用前定义切面,利用Spring的AbstractRoutingDataSource解决多数据源的问题,实现动态选择数据源

  • 优点:通过注解的方法在DAO每个方法上配置数据源,原有代码改动量少,易扩展,支持多读
  • 缺点:需要在DAO每个方法上配置注解,人工管理,容易出错
  • 实现方式

//定义枚举类型,读写
public enum DynamicDataSourceGlobal {
READ, WRITE;
}

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
* RUNTIME
* 定义注解
* 编译器将把注释记录在类文件中,在运行时 VM 将保留注释,因此可以反射性地读取。
* @author shma1664
*
*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface DataSource {

public DynamicDataSourceGlobal value() default DynamicDataSourceGlobal.READ;

}

/**
* Created by IDEA
* 本地线程设置和获取数据源信息
* User: mashaohua
* Date: 2016-07-07 13:35
* Desc:
*/
public class DynamicDataSourceHolder {

private static final ThreadLocal<DynamicDataSourceGlobal> holder = new ThreadLocal<DynamicDataSourceGlobal>();

public static void putDataSource(DynamicDataSourceGlobal dataSource){
holder.set(dataSource);
}

public static DynamicDataSourceGlobal getDataSource(){
return holder.get();
}

public static void clearDataSource() {
holder.remove();
}

}

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

import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
* Created by IDEA
* User: mashaohua
* Date: 2016-07-14 10:56
* Desc: 动态数据源实现读写分离
*/
public class DynamicDataSource extends AbstractRoutingDataSource {

private Object writeDataSource; //写数据源

private List<Object> readDataSources; //多个读数据源

private int readDataSourceSize; //读数据源个数

private int readDataSourcePollPattern = 0; //获取读数据源方式,0:随机,1:轮询

private AtomicLong counter = new AtomicLong(0);

private static final Long MAX_POOL = Long.MAX_VALUE;

private final Lock lock = new ReentrantLock();

@Override
public void afterPropertiesSet() {
if (this.writeDataSource == null) {
throw new IllegalArgumentException("Property 'writeDataSource' is required");
}
setDefaultTargetDataSource(writeDataSource);
Map<Object, Object> targetDataSources = new HashMap<>();
targetDataSources.put(DynamicDataSourceGlobal.WRITE.name(), writeDataSource);
if (this.readDataSources == null) {
readDataSourceSize = 0;
} else {
for(int i=0; i<readDataSources.size(); i++) {
targetDataSources.put(DynamicDataSourceGlobal.READ.name() + i, readDataSources.get(i));
}
readDataSourceSize = readDataSources.size();
}
setTargetDataSources(targetDataSources);
super.afterPropertiesSet();
}

@Override
protected Object determineCurrentLookupKey() {

DynamicDataSourceGlobal dynamicDataSourceGlobal = DynamicDataSourceHolder.getDataSource();

if(dynamicDataSourceGlobal == null
|| dynamicDataSourceGlobal == DynamicDataSourceGlobal.WRITE
|| readDataSourceSize <= 0) {
return DynamicDataSourceGlobal.WRITE.name();
}

int index = 1;

if(readDataSourcePollPattern == 1) {
//轮询方式
long currValue = counter.incrementAndGet();
if((currValue + 1) >= MAX_POOL) {
try {
lock.lock();
if((currValue + 1) >= MAX_POOL) {
counter.set(0);
}
} finally {
lock.unlock();
}
}
index = (int) (currValue % readDataSourceSize);
} else {
//随机方式
index = ThreadLocalRandom.current().nextInt(0, readDataSourceSize);
}
return dynamicDataSourceGlobal.name() + index;
}

public void setWriteDataSource(Object writeDataSource) {
this.writeDataSource = writeDataSource;
}

public void setReadDataSources(List<Object> readDataSources) {
this.readDataSources = readDataSources;
}

public void setReadDataSourcePollPattern(int readDataSourcePollPattern) {
this.readDataSourcePollPattern = readDataSourcePollPattern;
}
}

import org.apache.log4j.Logger;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.reflect.MethodSignature;

import java.lang.reflect.Method;

/**
* Created by IDEA
* User: mashaohua
* Date: 2016-07-07 13:39
* Desc: 定义选择数据源切面
*/
public class DynamicDataSourceAspect {

private static final Logger logger = Logger.getLogger(DynamicDataSourceAspect.class);

public void pointCut(){};

public void before(JoinPoint point)
{
Object target = point.getTarget();
String methodName = point.getSignature().getName();
Class<?>[] clazz = target.getClass().getInterfaces();
Class<?>[] parameterTypes = ((MethodSignature) point.getSignature()).getMethod().getParameterTypes();
try {
Method method = clazz[0].getMethod(methodName, parameterTypes);
if (method != null && method.isAnnotationPresent(DataSource.class)) {
DataSource data = method.getAnnotation(DataSource.class);
DynamicDataSourceHolder.putDataSource(data.value());
}
} catch (Exception e) {
logger.error(String.format("Choose DataSource error, method:%s, msg:%s", methodName, e.getMessage()));
}
}

public void after(JoinPoint point) {
DynamicDataSourceHolder.clearDataSource();
}
}

<?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:tx="http://www.springframework.org/schema/tx"
xmlns:aop="http://www.springframework.org/schema/aop"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-4.1.xsd
http://www.springframework.org/schema/tx
http://www.springframework.org/schema/tx/spring-tx-4.1.xsd
http://www.springframework.org/schema/aop
http://www.springframework.org/schema/aop/spring-aop-4.1.xsd">

<bean id="abstractDataSource" abstract="true" class="com.alibaba.druid.pool.DruidDataSource" init-method="init" destroy-method="close">
<property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
<!-- 配置获取连接等待超时的时间 -->
<property name="maxWait" value="60000"/>
<!-- 配置间隔多久才进行一次检测,检测需要关闭的空闲连接,单位是毫秒 -->
<property name="timeBetweenEvictionRunsMillis" value="60000"/>
<!-- 配置一个连接在池中最小生存的时间,单位是毫秒 -->
<property name="minEvictableIdleTimeMillis" value="300000"/>
<property name="validationQuery" value="SELECT 'x'"/>
<property name="testWhileIdle" value="true"/>
<property name="testOnBorrow" value="false"/>
<property name="testOnReturn" value="false"/>
<!-- 打开PSCache,并且指定每个连接上PSCache的大小 -->
<property name="poolPreparedStatements" value="true"/>
<property name="maxPoolPreparedStatementPerConnectionSize" value="20"/>
<property name="filters" value="config"/>
<property name="connectionProperties" value="config.decrypt=true" />
</bean>

<bean id="dataSourceRead1" parent="abstractDataSource">
<property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
<!-- 基本属性 url、user、password -->
<property name="url" value="${read1.jdbc.url}"/>
<property name="username" value="${read1.jdbc.user}"/>
<property name="password" value="${read1.jdbc.password}"/>
<!-- 配置初始化大小、最小、最大 -->
<property name="initialSize" value="${read1.jdbc.initPoolSize}"/>
<property name="minIdle" value="${read1.jdbc.minPoolSize}"/>
<property name="maxActive" value="${read1.jdbc.maxPoolSize}"/>
</bean>

<bean id="dataSourceRead2" parent="abstractDataSource">
<property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
<!-- 基本属性 url、user、password -->
<property name="url" value="${read2.jdbc.url}"/>
<property name="username" value="${read2.jdbc.user}"/>
<property name="password" value="${read2.jdbc.password}"/>
<!-- 配置初始化大小、最小、最大 -->
<property name="initialSize" value="${read2.jdbc.initPoolSize}"/>
<property name="minIdle" value="${read2.jdbc.minPoolSize}"/>
<property name="maxActive" value="${read2.jdbc.maxPoolSize}"/>
</bean>

<bean id="dataSourceWrite" parent="abstractDataSource">
<property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
<!-- 基本属性 url、user、password -->
<property name="url" value="${write.jdbc.url}"/>
<property name="username" value="${write.jdbc.user}"/>
<property name="password" value="${write.jdbc.password}"/>
<!-- 配置初始化大小、最小、最大 -->
<property name="initialSize" value="${write.jdbc.initPoolSize}"/>
<property name="minIdle" value="${write.jdbc.minPoolSize}"/>
<property name="maxActive" value="${write.jdbc.maxPoolSize}"/>
</bean>

<bean id="dataSource" class="com.test.api.dao.datasource.DynamicDataSource">
<property name="writeDataSource" ref="dataSourceWrite" />
<property name="readDataSources">
<list>
<ref bean="dataSourceRead1" />
<ref bean="dataSourceRead2" />
</list>
</property>
<!--轮询方式-->
<property name="readDataSourcePollPattern" value="1" />
<property name="defaultTargetDataSource" ref="dataSourceWrite"/>
</bean>

<tx:annotation-driven transaction-manager="transactionManager"/>

<bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
<property name="dataSource" ref="dataSource"/>
</bean>

<!-- 针对myBatis的配置项 -->
<!-- 配置sqlSessionFactory -->
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<!-- 实例化sqlSessionFactory时需要使用上述配置好的数据源以及SQL映射文件 -->
<property name="dataSource" ref="dataSource"/>
<property name="mapperLocations" value="classpath:mapper/*.xml"/>
</bean>

<!-- 配置扫描器 -->
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<!-- 扫描包以及它的子包下的所有映射接口类 -->
<property name="basePackage" value="com.test.api.dao.inte"/>
<property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"/>
</bean>

<!-- 配置数据库注解aop -->
<bean id="dynamicDataSourceAspect" class="com.test.api.dao.datasource.DynamicDataSourceAspect" />
<aop:config>
<aop:aspect id="c" ref="dynamicDataSourceAspect">
<aop:pointcut id="tx" expression="execution(* com.test.api.dao.inte..*.*(..))"/>
<aop:before pointcut-ref="tx" method="before"/>
<aop:after pointcut-ref="tx" method="after"/>
</aop:aspect>
</aop:config>
<!-- 配置数据库注解aop -->
</beans>

方案3

通过Mybatis的Plugin在业务层实现数据库读写分离,在MyBatis创建Statement对象前通过拦截器选择真正的数据源,在拦截器中根据方法名称不同(select、update、insert、delete)选择数据源。

  • 优点:原有代码不变,支持多读,易扩展
  • 缺点:
  • 实现方式

/**
* Created by IDEA
* User: mashaohua
* Date: 2016-07-19 15:40
* Desc: 创建Connection代理接口
*/
public interface ConnectionProxy extends Connection {

/**
* 根据传入的读写分离需要的key路由到正确的connection
* @param key 数据源标识
* @return
*/
Connection getTargetConnection(String key);
}

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Logger;

import javax.sql.DataSource;

import org.springframework.beans.factory.InitializingBean;
import org.springframework.jdbc.datasource.AbstractDataSource;
import org.springframework.jdbc.datasource.lookup.DataSourceLookup;
import org.springframework.jdbc.datasource.lookup.JndiDataSourceLookup;
import org.springframework.util.Assert;

public abstract class AbstractDynamicDataSourceProxy extends AbstractDataSource implements InitializingBean {

private List<Object> readDataSources;
private List<DataSource> resolvedReadDataSources;

private Object writeDataSource;
private DataSource resolvedWriteDataSource;

private int readDataSourcePollPattern = 0;

private int readDsSize;

private boolean defaultAutoCommit = true;
private int defaultTransactionIsolation = Connection.TRANSACTION_READ_COMMITTED;

public static final String READ = "read";

public static final String WRITE = "write";

private DataSourceLookup dataSourceLookup = new JndiDataSourceLookup();

@Override
public Connection getConnection() throws SQLException {
return (Connection) Proxy.newProxyInstance(
com.autohome.api.dealer.tuan.dao.rwmybatis.ConnectionProxy.class.getClassLoader(),
new Class[] {com.autohome.api.dealer.tuan.dao.rwmybatis.ConnectionProxy.class},
new RWConnectionInvocationHandler());
}

@Override
public Connection getConnection(String username, String password)
throws SQLException {
return (Connection) Proxy.newProxyInstance(
com.autohome.api.dealer.tuan.dao.rwmybatis.ConnectionProxy.class.getClassLoader(),
new Class[] {com.autohome.api.dealer.tuan.dao.rwmybatis.ConnectionProxy.class},
new RWConnectionInvocationHandler(username,password));
}

public int getReadDsSize(){
return readDsSize;
}

public List<DataSource> getResolvedReadDataSources() {
return resolvedReadDataSources;
}

public void afterPropertiesSet() throws Exception {

if(writeDataSource == null){
throw new IllegalArgumentException("Property 'writeDataSource' is required");
}
this.resolvedWriteDataSource = resolveSpecifiedDataSource(writeDataSource);

resolvedReadDataSources = new ArrayList<DataSource>(readDataSources.size());
for(Object item : readDataSources){
resolvedReadDataSources.add(resolveSpecifiedDataSource(item));
}
readDsSize = readDataSources.size();
}

protected DataSource determineTargetDataSource(String key) {
Assert.notNull(this.resolvedReadDataSources, "DataSource router not initialized");
if(WRITE.equals(key)){
return resolvedWriteDataSource;
}else{
return loadReadDataSource();
}
}

public Logger getParentLogger() {
// NOOP Just ignore
return null;
}

/**
* 获取真实的data source
* @param dataSource (jndi | real data source)
* @return
* @throws IllegalArgumentException
*/
protected DataSource resolveSpecifiedDataSource(Object dataSource) throws IllegalArgumentException {
if (dataSource instanceof DataSource) {
return (DataSource) dataSource;
}
else if (dataSource instanceof String) {
return this.dataSourceLookup.getDataSource((String) dataSource);
}
else {
throw new IllegalArgumentException(
"Illegal data source value - only [javax.sql.DataSource] and String supported: " + dataSource);
}
}

protected abstract DataSource loadReadDataSource();

public void setReadDsSize(int readDsSize) {
this.readDsSize = readDsSize;
}

public List<Object> getReadDataSources() {
return readDataSources;
}

public void setReadDataSources(List<Object> readDataSources) {
this.readDataSources = readDataSources;
}

public Object getWriteDataSource() {
return writeDataSource;
}

public void setWriteDataSource(Object writeDataSource) {
this.writeDataSource = writeDataSource;
}

public void setResolvedReadDataSources(List<DataSource> resolvedReadDataSources) {
this.resolvedReadDataSources = resolvedReadDataSources;
}

public DataSource getResolvedWriteDataSource() {
return resolvedWriteDataSource;
}

public void setResolvedWriteDataSource(DataSource resolvedWriteDataSource) {
this.resolvedWriteDataSource = resolvedWriteDataSource;
}

public int getReadDataSourcePollPattern() {
return readDataSourcePollPattern;
}

public void setReadDataSourcePollPattern(int readDataSourcePollPattern) {
this.readDataSourcePollPattern = readDataSourcePollPattern;
}

/**
* Invocation handler that defers fetching an actual JDBC Connection
* until first creation of a Statement.
*/
private class RWConnectionInvocationHandler implements InvocationHandler {

private String username;

private String password;

private Boolean readOnly = Boolean.FALSE;

private Integer transactionIsolation;

private Boolean autoCommit;

private boolean closed = false;

private Connection target;

public RWConnectionInvocationHandler() {

}

public RWConnectionInvocationHandler(String username, String password) {
this();
this.username = username;
this.password = password;
}

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
// Invocation on ConnectionProxy interface coming in...

if (method.getName().equals("equals")) {
// We must avoid fetching a target Connection for "equals".
// Only consider equal when proxies are identical.
return (proxy == args[0] ? Boolean.TRUE : Boolean.FALSE);
}
else if (method.getName().equals("hashCode")) {
// We must avoid fetching a target Connection for "hashCode",
// and we must return the same hash code even when the target
// Connection has been fetched: use hashCode of Connection proxy.
return new Integer(System.identityHashCode(proxy));
}
else if (method.getName().equals("getTargetConnection")) {
// Handle getTargetConnection method: return underlying connection.
return getTargetConnection(method,args);
}

if (!hasTargetConnection()) {
// No physical target Connection kept yet ->
// resolve transaction demarcation methods without fetching
// a physical JDBC Connection until absolutely necessary.

if (method.getName().equals("toString")) {
return "RW Routing DataSource Proxy";
}
else if (method.getName().equals("isReadOnly")) {
return this.readOnly;
}
else if (method.getName().equals("setReadOnly")) {
this.readOnly = (Boolean) args[0];
return null;
}
else if (method.getName().equals("getTransactionIsolation")) {
if (this.transactionIsolation != null) {
return this.transactionIsolation;
}
return defaultTransactionIsolation;
// Else fetch actual Connection and check there,
// because we didn't have a default specified.
}
else if (method.getName().equals("setTransactionIsolation")) {
this.transactionIsolation = (Integer) args[0];
return null;
}
else if (method.getName().equals("getAutoCommit")) {
if (this.autoCommit != null)
return this.autoCommit;
return defaultAutoCommit;
// Else fetch actual Connection and check there,
// because we didn't have a default specified.
}
else if (method.getName().equals("setAutoCommit")) {
this.autoCommit = (Boolean) args[0];
return null;
}
else if (method.getName().equals("commit")) {
// Ignore: no statements created yet.
return null;
}
else if (method.getName().equals("rollback")) {
// Ignore: no statements created yet.
return null;
}
else if (method.getName().equals("getWarnings")) {
return null;
}
else if (method.getName().equals("clearWarnings")) {
return null;
}
else if (method.getName().equals("isClosed")) {
return (this.closed ? Boolean.TRUE : Boolean.FALSE);
}
else if (method.getName().equals("close")) {
// Ignore: no target connection yet.
this.closed = true;
return null;
}
else if (this.closed) {
// Connection proxy closed, without ever having fetched a
// physical JDBC Connection: throw corresponding SQLException.
throw new SQLException("Illegal operation: connection is closed");
}
}

// Target Connection already fetched,
// or target Connection necessary for current operation ->
// invoke method on target connection.
try {
return method.invoke(target, args);
}
catch (InvocationTargetException ex) {
throw ex.getTargetException();
}
}

/**
* Return whether the proxy currently holds a target Connection.
*/
private boolean hasTargetConnection() {
return (this.target != null);
}

/**
* Return the target Connection, fetching it and initializing it if necessary.
*/
private Connection getTargetConnection(Method operation,Object[] args) throws SQLException {

if (this.target == null) {
String key = (String) args[0];
// No target Connection held -> fetch one.
if (logger.isDebugEnabled()) {
logger.debug("Connecting to database for operation '" + operation.getName() + "'");
}

// Fetch physical Connection from DataSource.
this.target = (this.username != null) ?
determineTargetDataSource(key).getConnection(this.username, this.password) :
determineTargetDataSource(key).getConnection();

// If we still lack default connection properties, check them now.
//checkDefaultConnectionProperties(this.target);

// Apply kept transaction settings, if any.
if (this.readOnly.booleanValue()) {
this.target.setReadOnly(this.readOnly.booleanValue());
}
if (this.transactionIsolation != null) {
this.target.setTransactionIsolation(this.transactionIsolation.intValue());
}
if (this.autoCommit != null && this.autoCommit.booleanValue() != this.target.getAutoCommit()) {
this.target.setAutoCommit(this.autoCommit.booleanValue());
}
}

else {
// Target Connection already held -> return it.
if (logger.isDebugEnabled()) {
logger.debug("Using existing database connection for operation '" + operation.getName() + "'");
}
}

return this.target;
}
}

}

import javax.sql.DataSource;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
* Created by IDEA
* User: mashaohua
* Date: 2016-07-19 16:04
* Desc:
*/
public class DynamicRoutingDataSourceProxy extends AbstractDynamicDataSourceProxy {

private AtomicLong counter = new AtomicLong(0);

private static final Long MAX_POOL = Long.MAX_VALUE;

private final Lock lock = new ReentrantLock();

@Override
protected DataSource loadReadDataSource() {
int index = 1;

if(getReadDataSourcePollPattern() == 1) {
//轮询方式
long currValue = counter.incrementAndGet();
if((currValue + 1) >= MAX_POOL) {
try {
lock.lock();
if((currValue + 1) >= MAX_POOL) {
counter.set(0);
}
} finally {
lock.unlock();
}
}
index = (int) (currValue % getReadDsSize());
} else {
//随机方式
index = ThreadLocalRandom.current().nextInt(0, getReadDsSize());
}
return getResolvedReadDataSources().get(index);
}
}

import org.apache.ibatis.executor.statement.RoutingStatementHandler;
import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.SqlCommandType;
import org.apache.ibatis.plugin.*;

import java.sql.Connection;
import java.util.Properties;

/**
* 拦截器
*/
@Intercepts({ @Signature(type = StatementHandler.class, method = "prepare", args = { Connection.class }) })
public class DynamicPlugin implements Interceptor {

public Object intercept(Invocation invocation) throws Throwable {


Connection conn = (Connection)invocation.getArgs()[0];
//如果是采用了我们代理,则路由数据源
if(conn instanceof com.autohome.api.dealer.tuan.dao.rwmybatis.ConnectionProxy){
StatementHandler statementHandler = (StatementHandler) invocation
.getTarget();

MappedStatement mappedStatement = null;
if (statementHandler instanceof RoutingStatementHandler) {
StatementHandler delegate = (StatementHandler) ReflectionUtils
.getFieldValue(statementHandler, "delegate");
mappedStatement = (MappedStatement) ReflectionUtils.getFieldValue(
delegate, "mappedStatement");
} else {
mappedStatement = (MappedStatement) ReflectionUtils.getFieldValue(
statementHandler, "mappedStatement");
}
String key = AbstractDynamicDataSourceProxy.WRITE;

if(mappedStatement.getSqlCommandType() == SqlCommandType.SELECT){
key = AbstractDynamicDataSourceProxy.READ;
}else{
key = AbstractDynamicDataSourceProxy.WRITE;
}

ConnectionProxy connectionProxy = (ConnectionProxy)conn;
connectionProxy.getTargetConnection(key);

}

return invocation.proceed();

}

public Object plugin(Object target) {

return Plugin.wrap(target, this);
}

public void setProperties(Properties properties) {
//NOOP

}

}

import org.apache.ibatis.logging.Log;
import org.apache.ibatis.logging.LogFactory;

import java.lang.reflect.*;

public class ReflectionUtils {

private static final Log logger = LogFactory.getLog(ReflectionUtils.class);

/**
* 直接设置对象属性值,无视private/protected修饰符,不经过setter函数.
*/
public static void setFieldValue(final Object object, final String fieldName, final Object value) {
Field field = getDeclaredField(object, fieldName);

if (field == null)
throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]");

makeAccessible(field);

try {
field.set(object, value);
} catch (IllegalAccessException e) {

}
}

/**
* 直接读取对象属性值,无视private/protected修饰符,不经过getter函数.
*/
public static Object getFieldValue(final Object object, final String fieldName) {
Field field = getDeclaredField(object, fieldName);

if (field == null)
throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]");

makeAccessible(field);

Object result = null;
try {
result = field.get(object);
} catch (IllegalAccessException e) {

}
return result;
}

/**
* 直接调用对象方法,无视private/protected修饰符.
*/
public static Object invokeMethod(final Object object, final String methodName, final Class<?>[] parameterTypes,
final Object[] parameters) throws InvocationTargetException {
Method method = getDeclaredMethod(object, methodName, parameterTypes);
if (method == null)
throw new IllegalArgumentException("Could not find method [" + methodName + "] on target [" + object + "]");

method.setAccessible(true);

try {
return method.invoke(object, parameters);
} catch (IllegalAccessException e) {

}

return null;
}

/**
* 循环向上转型,获取对象的DeclaredField.
*/
protected static Field getDeclaredField(final Object object, final String fieldName) {
for (Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass
.getSuperclass()) {
try {
return superClass.getDeclaredField(fieldName);
} catch (NoSuchFieldException e) {
}
}
return null;
}

/**
* 循环向上转型,获取对象的DeclaredField.
*/
protected static void makeAccessible(final Field field) {
if (!Modifier.isPublic(field.getModifiers()) || !Modifier.isPublic(field.getDeclaringClass().getModifiers())) {
field.setAccessible(true);
}
}

/**
* 循环向上转型,获取对象的DeclaredMethod.
*/
protected static Method getDeclaredMethod(Object object, String methodName, Class<?>[] parameterTypes) {
for (Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass
.getSuperclass()) {
try {
return superClass.getDeclaredMethod(methodName, parameterTypes);
} catch (NoSuchMethodException e) {

}
}
return null;
}

/**
* 通过反射,获得Class定义中声明的父类的泛型参数的类型.
* eg.
* public UserDao extends HibernateDao<User>
*
* @param clazz The class to introspect
* @return the first generic declaration, or Object.class if cannot be determined
*/
@SuppressWarnings("unchecked")
public static <T> Class<T> getSuperClassGenricType(final Class clazz) {
return getSuperClassGenricType(clazz, 0);
}

/**
* 通过反射,获得Class定义中声明的父类的泛型参数的类型.
* eg.
* public UserDao extends HibernateDao<User>
*
* @param clazz The class to introspect
* @return the first generic declaration, or Object.class if cannot be determined
*/
@SuppressWarnings("unchecked")
public static Class getSuperClassGenricType(final Class clazz, final int index) {

Type genType = clazz.getGenericSuperclass();

if (!(genType instanceof ParameterizedType)) {
logger.warn(clazz.getSimpleName() + "'s superclass not ParameterizedType");
return Object.class;
}

Type[] params = ((ParameterizedType) genType).getActualTypeArguments();

if (index >= params.length || index < 0) {
logger.warn("Index: " + index + ", Size of " + clazz.getSimpleName() + "'s Parameterized Type: "
+ params.length);
return Object.class;
}
if (!(params[index] instanceof Class)) {
logger.warn(clazz.getSimpleName() + " not set the actual class on superclass generic parameter");
return Object.class;
}

return (Class) params[index];
}

/**
* 将反射时的checked exception转换为unchecked exception.
*/
public static IllegalArgumentException convertToUncheckedException(Exception e) {
if (e instanceof IllegalAccessException || e instanceof IllegalArgumentException
|| e instanceof NoSuchMethodException)
return new IllegalArgumentException("Refelction Exception.", e);
else
return new IllegalArgumentException(e);
}
}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD SQL Map Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<plugins>
<plugin interceptor="com.test.api.dao.mybatis.DynamicPlugin">
</plugin>
</plugins>

</configuration>

<?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:tx="http://www.springframework.org/schema/tx"
xmlns:aop="http://www.springframework.org/schema/aop"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-4.1.xsd
http://www.springframework.org/schema/tx
http://www.springframework.org/schema/tx/spring-tx-4.1.xsd
http://www.springframework.org/schema/aop
http://www.springframework.org/schema/aop/spring-aop-4.1.xsd">

<bean id="abstractDataSource" abstract="true" class="com.alibaba.druid.pool.DruidDataSource" init-method="init" destroy-method="close">
<property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
<!-- 配置获取连接等待超时的时间 -->
<property name="maxWait" value="60000"/>
<!-- 配置间隔多久才进行一次检测,检测需要关闭的空闲连接,单位是毫秒 -->
<property name="timeBetweenEvictionRunsMillis" value="60000"/>
<!-- 配置一个连接在池中最小生存的时间,单位是毫秒 -->
<property name="minEvictableIdleTimeMillis" value="300000"/>
<property name="validationQuery" value="SELECT 'x'"/>
<property name="testWhileIdle" value="true"/>
<property name="testOnBorrow" value="false"/>
<property name="testOnReturn" value="false"/>
<!-- 打开PSCache,并且指定每个连接上PSCache的大小 -->
<property name="poolPreparedStatements" value="true"/>
<property name="maxPoolPreparedStatementPerConnectionSize" value="20"/>
<property name="filters" value="config"/>
<property name="connectionProperties" value="config.decrypt=true" />
</bean>

<bean id="dataSourceRead1" parent="abstractDataSource">
<property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
<!-- 基本属性 url、user、password -->
<property name="url" value="${read1.jdbc.url}"/>
<property name="username" value="${read1.jdbc.user}"/>
<property name="password" value="${read1.jdbc.password}"/>
<!-- 配置初始化大小、最小、最大 -->
<property name="initialSize" value="${read1.jdbc.initPoolSize}"/>
<property name="minIdle" value="${read1.jdbc.minPoolSize}"/>
<property name="maxActive" value="${read1.jdbc.maxPoolSize}"/>
</bean>

<bean id="dataSourceRead2" parent="abstractDataSource">
<property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
<!-- 基本属性 url、user、password -->
<property name="url" value="${read2.jdbc.url}"/>
<property name="username" value="${read2.jdbc.user}"/>
<property name="password" value="${read2.jdbc.password}"/>
<!-- 配置初始化大小、最小、最大 -->
<property name="initialSize" value="${read2.jdbc.initPoolSize}"/>
<property name="minIdle" value="${read2.jdbc.minPoolSize}"/>
<property name="maxActive" value="${read2.jdbc.maxPoolSize}"/>
</bean>

<bean id="dataSourceWrite" parent="abstractDataSource">
<property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
<!-- 基本属性 url、user、password -->
<property name="url" value="${write.jdbc.url}"/>
<property name="username" value="${write.jdbc.user}"/>
<property name="password" value="${write.jdbc.password}"/>
<!-- 配置初始化大小、最小、最大 -->
<property name="initialSize" value="${write.jdbc.initPoolSize}"/>
<property name="minIdle" value="${write.jdbc.minPoolSize}"/>
<property name="maxActive" value="${write.jdbc.maxPoolSize}"/>
</bean>

<bean id="dataSource" class="com.test.api.dao.datasource.DynamicRoutingDataSourceProxy">
<property name="writeDataSource" ref="dataSourceWrite" />
<property name="readDataSources">
<list>
<ref bean="dataSourceRead1" />
<ref bean="dataSourceRead2" />
</list>
</property>
<!--轮询方式-->
<property name="readDataSourcePollPattern" value="1" />
</bean>

<tx:annotation-driven transaction-manager="transactionManager"/>

<bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
<property name="dataSource" ref="dataSource"/>
</bean>

<!-- 针对myBatis的配置项 -->
<!-- 配置sqlSessionFactory -->
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<!-- 实例化sqlSessionFactory时需要使用上述配置好的数据源以及SQL映射文件 -->
<property name="dataSource" ref="dataSource"/>
<property name="mapperLocations" value="classpath:mapper/*.xml"/>
<property name="configLocation" value="classpath:mybatis-plugin-config.xml" />
</bean>

<bean id="sqlSessionTemplate" class="org.mybatis.spring.SqlSessionTemplate">
<constructor-arg ref="sqlSessionFactory" />
</bean>
<!-- 通过扫描的模式,扫描目录下所有的mapper, 根据对应的mapper.xml为其生成代理类-->
<bean id="mapper" class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<property name="basePackage" value="com.test.api.dao.inte" />
<property name="sqlSessionTemplate" ref="sqlSessionTemplate"></property>
</bean>

</beans>

方案4

如果你的后台结构是spring+mybatis,可以通过spring的AbstractRoutingDataSource和mybatis Plugin拦截器实现非常友好的读写分离,原有代码不需要任何改变。推荐第四种方案

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

import java.util.HashMap;
import java.util.Map;

/**
* Created by IDEA
* User: mashaohua
* Date: 2016-07-14 10:56
* Desc: 动态数据源实现读写分离
*/
public class DynamicDataSource extends AbstractRoutingDataSource {

private Object writeDataSource; //写数据源

private Object readDataSource; //读数据源

@Override
public void afterPropertiesSet() {
if (this.writeDataSource == null) {
throw new IllegalArgumentException("Property 'writeDataSource' is required");
}
setDefaultTargetDataSource(writeDataSource);
Map<Object, Object> targetDataSources = new HashMap<>();
targetDataSources.put(DynamicDataSourceGlobal.WRITE.name(), writeDataSource);
if(readDataSource != null) {
targetDataSources.put(DynamicDataSourceGlobal.READ.name(), readDataSource);
}
setTargetDataSources(targetDataSources);
super.afterPropertiesSet();
}

@Override
protected Object determineCurrentLookupKey() {

DynamicDataSourceGlobal dynamicDataSourceGlobal = DynamicDataSourceHolder.getDataSource();

if(dynamicDataSourceGlobal == null
|| dynamicDataSourceGlobal == DynamicDataSourceGlobal.WRITE) {
return DynamicDataSourceGlobal.WRITE.name();
}

return DynamicDataSourceGlobal.READ.name();
}

public void setWriteDataSource(Object writeDataSource) {
this.writeDataSource = writeDataSource;
}

public Object getWriteDataSource() {
return writeDataSource;
}

public Object getReadDataSource() {
return readDataSource;
}

public void setReadDataSource(Object readDataSource) {
this.readDataSource = readDataSource;
}
}

/**
* Created by IDEA
* User: mashaohua
* Date: 2016-07-14 10:58
* Desc:
*/
public enum DynamicDataSourceGlobal {
READ, WRITE;
}

public final class DynamicDataSourceHolder {

private static final ThreadLocal<DynamicDataSourceGlobal> holder = new ThreadLocal<DynamicDataSourceGlobal>();

private DynamicDataSourceHolder() {
//
}

public static void putDataSource(DynamicDataSourceGlobal dataSource){
holder.set(dataSource);
}

public static DynamicDataSourceGlobal getDataSource(){
return holder.get();
}

public static void clearDataSource() {
holder.remove();
}

}

import org.springframework.jdbc.datasource.DataSourceTransactionManager;
import org.springframework.transaction.TransactionDefinition;

/**
* Created by IDEA
* User: mashaohua
* Date: 2016-08-10 14:34
* Desc:
*/
public class DynamicDataSourceTransactionManager extends DataSourceTransactionManager {

/**
* 只读事务到读库,读写事务到写库
* @param transaction
* @param definition
*/
@Override
protected void doBegin(Object transaction, TransactionDefinition definition) {

//设置数据源
boolean readOnly = definition.isReadOnly();
if(readOnly) {
DynamicDataSourceHolder.putDataSource(DynamicDataSourceGlobal.READ);
} else {
DynamicDataSourceHolder.putDataSource(DynamicDataSourceGlobal.WRITE);
}
super.doBegin(transaction, definition);
}

/**
* 清理本地线程的数据源
* @param transaction
*/
@Override
protected void doCleanupAfterCompletion(Object transaction) {
super.doCleanupAfterCompletion(transaction);
DynamicDataSourceHolder.clearDataSource();
}
}

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.*;
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;

import java.util.Locale;
import java.util.Map;
import java.util.Properties;
import java.util.concurrent.ConcurrentHashMap;

/**
* Created by IDEA
* User: mashaohua
* Date: 2016-08-10 11:09
* Desc:
*/
@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 DynamicPlugin implements Interceptor {

protected static final Logger logger = LoggerFactory.getLogger(DynamicPlugin.class);

private static final String REGEX = ".*insert\\u0020.*|.*delete\\u0020.*|.*update\\u0020.*";

private static final Map<String, DynamicDataSourceGlobal> cacheMap = new ConcurrentHashMap<>();

@Override
public Object intercept(Invocation invocation) throws Throwable {

boolean synchronizationActive = TransactionSynchronizationManager.isSynchronizationActive();
if(!synchronizationActive) {
Object[] objects = invocation.getArgs();
MappedStatement ms = (MappedStatement) objects[0];

DynamicDataSourceGlobal dynamicDataSourceGlobal = null;

if((dynamicDataSourceGlobal = cacheMap.get(ms.getId())) == null) {
//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)) {
dynamicDataSourceGlobal = DynamicDataSourceGlobal.WRITE;
} else {
BoundSql boundSql = ms.getSqlSource().getBoundSql(objects[1]);
String sql = boundSql.getSql().toLowerCase(Locale.CHINA).replaceAll("[\\t\\n\\r]", " ");
if(sql.matches(REGEX)) {
dynamicDataSourceGlobal = DynamicDataSourceGlobal.WRITE;
} else {
dynamicDataSourceGlobal = DynamicDataSourceGlobal.READ;
}
}
}else{
dynamicDataSourceGlobal = DynamicDataSourceGlobal.WRITE;
}
logger.warn("设置方法[{}] use [{}] Strategy, SqlCommandType [{}]..", ms.getId(), dynamicDataSourceGlobal.name(), ms.getSqlCommandType().name());
cacheMap.put(ms.getId(), dynamicDataSourceGlobal);
}
DynamicDataSourceHolder.putDataSource(dynamicDataSourceGlobal);
}

return invocation.proceed();
}

@Override
public Object plugin(Object target) {
if (target instanceof Executor) {
return Plugin.wrap(target, this);
} else {
return target;
}
}

@Override
public void setProperties(Properties properties) {
//
}

推荐第四种:https://github.com/shawntime/shawn-rwdb

文章目录
  1. 1. 方案1
  2. 2. 方案2
  3. 3. 方案3
  4. 4. 方案4