前言

      Sharding-JDBC是一个开源的分布式数据库中间件，它无需额外部署和依赖，完全兼容JDBC和各种ORM框架。Sharding-JDBC作为面向开发的微服务云原生基础类库，完整的实现了分库分表、读写分离和分布式主键功能，并初步实现了柔性事务。

以2.0.3版本为例maven包依赖如下

<project xmlns="http://maven.apache.org/POM/4.0.0" 	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> 	<modelVersion>4.0.0</modelVersion>  	<groupId>com.dongpeng</groupId> 	<artifactId>sharding-jdbc</artifactId> 	<version>1.0.0</version> 	<packaging>jar</packaging>  	<name>sharding-jdbc</name> 	<url>http://maven.apache.org</url>  	<properties> 		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> 	</properties>  	<dependencies> 		<dependency> 			<groupId>io.shardingjdbc</groupId> 			<artifactId>sharding-jdbc-core</artifactId> 			<version>2.0.3</version> 		</dependency>  		<dependency> 			<groupId>com.google.guava</groupId> 			<artifactId>guava</artifactId> 			<version>23.0</version> 		</dependency> 		<dependency> 			<groupId>com.mchange</groupId> 			<artifactId>c3p0</artifactId>  			<version>0.9.5.2</version> 		</dependency> 		<dependency> 			<groupId>mysql</groupId> 			<artifactId>mysql-connector-java</artifactId> 			<version>5.1.46</version> 		</dependency> 		<dependency> 			<groupId>log4j</groupId> 			<artifactId>log4j</artifactId> 			<version>1.2.17</version> 		</dependency> 		<dependency> 			<groupId>org.slf4j</groupId> 			<artifactId>slf4j-api</artifactId> 			<version>1.7.21</version> 		</dependency>  		<dependency> 			<groupId>org.slf4j</groupId> 			<artifactId>slf4j-log4j12</artifactId> 			<version>1.7.21</version> 		</dependency>  	</dependencies> 	<build> 		<resources> 			<resource> 				<directory>src/main/java</directory> 			</resource> 			<resource> 				<directory>src/main/resources</directory> 			</resource> 		</resources> 		<plugins>  			<plugin> 				<groupId>org.apache.maven.plugins</groupId> 				<artifactId>maven-compiler-plugin</artifactId> 				<configuration> 					<source>1.8</source> 					<target>1.8</target> 					<encoding>UTF-8</encoding> 				</configuration> 			</plugin> 		</plugins> 	</build> </project> 

demo实现如下

package com.dongpeng.sharding.jdbc;  import java.sql.Connection; import java.sql.ResultSet; import java.sql.Statement; import java.util.HashMap; import java.util.Map;  import javax.sql.DataSource;  import com.mchange.v2.c3p0.ComboPooledDataSource;  import io.shardingjdbc.core.api.MasterSlaveDataSourceFactory; import io.shardingjdbc.core.api.config.MasterSlaveRuleConfiguration; /**  * sharding-jdbc读写分离  * @author Admin  *  */ public class MasterSalveDemo { 	public static void main(String[] args) throws Exception { 		Map<String, DataSource> dataSourceMap = new HashMap<String, DataSource>(); 		ComboPooledDataSource dataSource1 = new ComboPooledDataSource(); 		dataSource1.setDriverClass("com.mysql.jdbc.Driver"); // loads the jdbc driver 		dataSource1.setJdbcUrl("jdbc:mysql://localhost:3306/db_0?useSSL=false"); 		dataSource1.setUser("root"); 		dataSource1.setPassword("root"); 		dataSourceMap.put("ds_0", dataSource1);  		ComboPooledDataSource dataSource2 = new ComboPooledDataSource(); 		dataSource2.setDriverClass("com.mysql.jdbc.Driver"); // loads the jdbc driver 		dataSource2.setJdbcUrl("jdbc:mysql://localhost:3306/db_1?useSSL=false"); 		dataSource2.setUser("root"); 		dataSource2.setPassword("root"); 		dataSourceMap.put("ds_1", dataSource2);  		MasterSlaveRuleConfiguration masterSlaveRuleConfig = new MasterSlaveRuleConfiguration(); 		masterSlaveRuleConfig.setName("ms_ds"); 		masterSlaveRuleConfig.setMasterDataSourceName("ds_0"); 		masterSlaveRuleConfig.getSlaveDataSourceNames().add("ds_1");  		DataSource dataSource = MasterSlaveDataSourceFactory.createDataSource(dataSourceMap, masterSlaveRuleConfig, 				new HashMap<String, Object>()); 		Connection connection = dataSource.getConnection(); 		Statement statement = connection.createStatement(); 		ResultSet rs = statement.executeQuery("select * from t_order_0 where user_id=1"); 		while (rs.next()) { 			System.out.println(rs.getString("order_id")); 		}  		statement.close(); 		connection.close(); 	} } 

源码解析

   主要的几个类

    MasterSlaveRuleConfiguration

    MasterSlaveDataSourceFactory

    MasterSlaveConnection

    MasterSlaveDataSource

    MasterSlaveStatement

    MasterSlavePreparedStatement

   各个类的说明如下

    MasterSalveRuleConfiguration

  是一个配置类用于配置主从的一些参数，主要的配置参数如下

    private String name;          private String masterDataSourceName;          private Collection<String> slaveDataSourceNames = new LinkedList<>();          private MasterSlaveLoadBalanceAlgorithmType loadBalanceAlgorithmType;          private String loadBalanceAlgorithmClassName;

name在独立的读写分离模式中，目前在策略接口中有使用

masterDataSourceName配置主节点dataSource

slaveDataSourceNames 提供从节点dataSource配置

loadBalanceAlgorithmType配置默认的从节点选取策略，默认支持两种一是轮询()，二是随机(由类RandomMasterSlaveLoadBalanceAlgorithm实现)

loadBanceAlgorithmClassName 配置自定义实现的从节点选取策略，可根据自己的需求自定义实现，loadBalanceAlgorithmType配置优于自定义配置要这个类启作用，不要配置loadBalanceAlgorithmType

MasterSlaveDataSourceFactory

这个是个DataSource的工厂类实现，用于提供各种终端的配置载入方式,支持文件，自配置等等

  public static DataSource createDataSource(final Map<String, DataSource> dataSourceMap, final MasterSlaveRuleConfiguration masterSlaveRuleConfig,                                                final Map<String, Object> configMap) throws SQLException {         return new MasterSlaveDataSource(masterSlaveRuleConfig.build(dataSourceMap), configMap);     }

  public static DataSource createDataSource(final File yamlFile) throws SQLException, IOException {         YamlMasterSlaveConfiguration config = unmarshal(yamlFile);         return new MasterSlaveDataSource(config.getMasterSlaveRule(Collections.<String, DataSource>emptyMap()), config.getMasterSlaveRule().getConfigMap());     }

MasterSlaveDataSource

主要用于构建dataSource的信息，同时提供一些dataSource的选取方法，主要的先取方法如下

 public NamedDataSource getDataSource(final SQLType sqlType) {         if (isMasterRoute(sqlType)) {             DML_FLAG.set(true);             return new NamedDataSource(masterSlaveRule.getMasterDataSourceName(), masterSlaveRule.getMasterDataSource());         }         String selectedSourceName = masterSlaveRule.getStrategy().getDataSource(masterSlaveRule.getName(),                  masterSlaveRule.getMasterDataSourceName(), new ArrayList<>(masterSlaveRule.getSlaveDataSourceMap().keySet()));         DataSource selectedSource = selectedSourceName.equals(masterSlaveRule.getMasterDataSourceName())                 ? masterSlaveRule.getMasterDataSource() : masterSlaveRule.getSlaveDataSourceMap().get(selectedSourceName);         Preconditions.checkNotNull(selectedSource, "");         return new NamedDataSource(selectedSourceName, selectedSource);     }

MasterSlaveConnection

MasterSlaveConnection是继承自AbstractConnectionAdapter的类，实现了connection接口，主要提供MasterSlaveStatement和MasterSlavePreparedStatement构建方式

如下几个方法

 @Override     public Statement createStatement() throws SQLException {         return new MasterSlaveStatement(this);     }

  @Override     public PreparedStatement prepareStatement(final String sql) throws SQLException {         return new MasterSlavePreparedStatement(this, sql);     }

同是提供connection的获取方式方法如下，在MasterSlaveStatement,MasterSlavePreparedStatement中有使用到

   public Collection<Connection> getConnections(final SQLType sqlType) throws SQLException {         cachedSQLType = sqlType;         Map<String, DataSource> dataSources = SQLType.DDL == sqlType ? masterSlaveDataSource.getMasterDataSource() : masterSlaveDataSource.getDataSource(sqlType).toMap();         Collection<Connection> result = new LinkedList<>();         for (Entry<String, DataSource> each : dataSources.entrySet()) {             String dataSourceName = each.getKey();             if (getCachedConnections().containsKey(dataSourceName)) {                 result.add(getCachedConnections().get(dataSourceName));                 continue;             }             Connection connection = each.getValue().getConnection();             getCachedConnections().put(dataSourceName, connection);             result.add(connection);             replayMethodsInvocation(connection);         }         return result;     }

MasterSlavePreparedStatement和MasterSlaveStatement

这两类都是对PreparedStatement和SlaveStatement的封装,提供了他们对应的sql执行方法，两类执行的方法都会调用Connection的获取方式如下两行代码，最终执行jdbc本身的实现，详情可以查看源码

  SQLStatement sqlStatement = new SQLJudgeEngine(sql).judge();   Collection<Connection> connections = connection.getConnections(sqlStatement.getType());

SQLStatement是一个sql类型解析类，sharding-jdbc实现了自己的一套sql的解析规则代码如下

/*  * Copyright 1999-2015 dangdang.com.  * <p>  * Licensed under the Apache License, Version 2.0 (the "License");  * you may not use this file except in compliance with the License.  * You may obtain a copy of the License at  *  *      http://www.apache.org/licenses/LICENSE-2.0  *  * Unless required by applicable law or agreed to in writing, software  * distributed under the License is distributed on an "AS IS" BASIS,  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  * See the License for the specific language governing permissions and  * limitations under the License.  * </p>  */  package io.shardingjdbc.core.parsing;  import io.shardingjdbc.core.parsing.lexer.Lexer; import io.shardingjdbc.core.parsing.lexer.analyzer.Dictionary; import io.shardingjdbc.core.parsing.lexer.token.Assist; import io.shardingjdbc.core.parsing.lexer.token.DefaultKeyword; import io.shardingjdbc.core.parsing.lexer.token.Keyword; import io.shardingjdbc.core.parsing.lexer.token.TokenType; import io.shardingjdbc.core.parsing.parser.exception.SQLParsingException; import io.shardingjdbc.core.parsing.parser.sql.SQLStatement; import io.shardingjdbc.core.parsing.parser.sql.ddl.DDLStatement; import io.shardingjdbc.core.parsing.parser.sql.dml.DMLStatement; import io.shardingjdbc.core.parsing.parser.sql.dql.select.SelectStatement; import lombok.RequiredArgsConstructor;  /**  * SQL judge engine.  *  * @author zhangliang  */ @RequiredArgsConstructor public final class SQLJudgeEngine {          private final String sql;          /**      * judge SQL Type only.      *      * @return SQL statement      */     public SQLStatement judge() {         Lexer lexer = new Lexer(sql, new Dictionary());         lexer.nextToken();         while (true) {             TokenType tokenType = lexer.getCurrentToken().getType();             if (tokenType instanceof Keyword) {                 if (DefaultKeyword.SELECT == tokenType) {                     return new SelectStatement();                 }                 if (DefaultKeyword.INSERT == tokenType || DefaultKeyword.UPDATE == tokenType || DefaultKeyword.DELETE == tokenType) {                     return new DMLStatement();                 }                 if (DefaultKeyword.CREATE == tokenType || DefaultKeyword.ALTER == tokenType || DefaultKeyword.DROP == tokenType || DefaultKeyword.TRUNCATE == tokenType) {                     return new DDLStatement();                 }             }             if (tokenType instanceof Assist && Assist.END == tokenType) {                 throw new SQLParsingException("Unsupported SQL statement: [%s]", sql);             }             lexer.nextToken();         }     } }