SpringBoot+Mybatis-Plus实现mysql读写分离方案的示例代码

1. 引入mybatis-plus相关包，pom.xml文件

2. 配置文件application.property增加多库配置

mysql 数据源配置

spring.datasource.primary.jdbc-url=jdbc:mysql://xx.xx.xx.xx:3306/portal?useunicode=true&usejdbccomplianttimezoneshift=true&uselegacydatetimecode=false&servertimezone=utc&characterencoding=utf8&servertimezone=gmt%2b8
spring.datasource.primary.username=root
spring.datasource.primary.password=root
spring.datasource.primary.driver-class-name=com.mysql.cj.jdbc.driver
#mysql slave 数据源配置

spring.datasource.slave.jdbc-url=jdbc:mysql://xx.xx.xx.xx:3306/portal?useunicode=true&usejdbccomplianttimezoneshift=true&uselegacydatetimecode=false&servertimezone=utc&characterencoding=utf8&servertimezone=gmt%2b8
spring.datasource.slave.username=root
spring.datasource.slave.password=root
spring.datasource.slave.driver-class-name=com.mysql.cj.jdbc.driver

3. 配置数据源及注解

数据源配置 multidatasourceconfig.java

/**
 * 配置多数据源
 */
@profile("dev")//开发模式配置文件
@configuration
@mapperscan(basepackages = "com.csc.portal.mapper")//扫描包
public class multidatasourceconfig {

  /**
   * 主数据源
   * @return
   */
  @bean
  @configurationproperties(prefix = "spring.datasource.primary")
  public datasource masterdatasource() {
    return datasourcebuilder.create().build();
  }

  /**
   * 从数据源
   * @return
   */
  @bean
  @configurationproperties(prefix = "spring.datasource.slave")
  public datasource slavedatasource() {
    return datasourcebuilder.create().build();
  }

  /**
   * 路由数据源，前面两个数据源是为了创建此数据源
   * @param masterdatasource 主数据源
   * @param slavedatasource 从数据源
   * @return
   */
  @bean
  public datasource myroutingdatasource(@qualifier("masterdatasource") datasource masterdatasource,
                     @qualifier("slavedatasource") datasource slavedatasource) {
    map<object, object> targetdatasources = new hashmap<>();
    targetdatasources.put(dbtypeenum.master, masterdatasource);
    targetdatasources.put(dbtypeenum.slave, slavedatasource);
    myroutingdatasource myroutingdatasource = new myroutingdatasource();
    myroutingdatasource.setdefaulttargetdatasource(slavedatasource);//设置默认数据源
    myroutingdatasource.settargetdatasources(targetdatasources);//设置路由表，使用map的key，value方式得到对应数据源
    return myroutingdatasource;
  }

数据库枚举类

public enum dbtypeenum {
 master, slave;
}

注解

@target({elementtype.method})
@retention(retentionpolicy.runtime)
public @interface master {
}

@target({elementtype.method})
@retention(retentionpolicy.runtime)
public @interface slave {
}

4. mybatis-plus配置

@enabletransactionmanagement
@configuration
@mapperscan(basepackages = "com.csc.portal.mapper")
public class mybatisplusconfig {
  /**
  * 分页插件
  */
  @bean
  public paginationinterceptor paginationinterceptor() {
    return new paginationinterceptor();
  }

  @resource(name = "myroutingdatasource")
  private datasource myroutingdatasource;
  /**
  * 使用mybatis plus的sqlsessionfactory代替，
  * 此处注意mybatis与mybatisplus的配置不同，不然扫描不到对数据操作的方法。会报未绑定错误
  * @return sqlsessionfactory
  * @throws exception
  */
  @bean
  public sqlsessionfactory sqlsessionfactory() throws exception {
    mybatissqlsessionfactorybean sqlsessionfactorybean = new mybatissqlsessionfactorybean();
    sqlsessionfactorybean.setdatasource(myroutingdatasource);
    sqlsessionfactorybean.setmapperlocations(new pathmatchingresourcepatternresolver().getresources("classpath:mapper/*.xml"));
    mybatisconfiguration mybatisconfiguration = new mybatisconfiguration();
    sqlsessionfactorybean.setconfiguration(mybatisconfiguration);
    return sqlsessionfactorybean.getobject();
  }

  /**
  * 此处为使用mybatis时的sqlsessionfactory配置
  * @return
  * @throws exception
  */
  /*
  @bean
  public sqlsessionfactory sqlsessionfactory() throws exception {
    sqlsessionfactorybean sqlsessionfactorybean = new sqlsessionfactorybean();
    sqlsessionfactorybean.setdatasource(myroutingdatasource);
    sqlsessionfactorybean.setmapperlocations(new pathmatchingresourcepatternresolver().getresources("classpath:mapper/*.xml"));
    return sqlsessionfactorybean.getobject();
  }
  */

  /**
  * 事务配置
  * @return 事务管理器
  */
  @bean
  public datasourcetransactionmanager transactionmanager() {
    datasourcetransactionmanager tx = new datasourcetransactionmanager();
    tx.setdatasource(myroutingdatasource);
    return tx;
  }

5. 增加数据源管理类

dbcontextholder.java

public class dbcontextholder {

  /**
   * 外部一个请求将会产生一个线程与之对应，每个线程的变量可用threadlocal进行存储
   */
  private static final threadlocal<dbtypeenum> contextholder = new threadlocal<>();

  public static void set(dbtypeenum dbtype) {
    contextholder.set(dbtype);
  }

  public static dbtypeenum get() {
    return contextholder.get();
  }

  public static void master() {
    set(dbtypeenum.master);
    system.out.println("切换到master");
  }

  public static void slave() {
    set(dbtypeenum.slave);
    system.out.println("切换到slave");
  }

}

指定选择数据源

myroutingdatasource.java 方法determinecurrentlookupkey决定最终使用哪个数据源进行操作，若为空则使用默认数据源。

public class myroutingdatasource extends abstractroutingdatasource {
  @nullable
  @override
  protected object determinecurrentlookupkey() {
    system.out.println("线程名："+thread.currentthread().getname()+":"+dbcontextholder.get());
    return dbcontextholder.get();
/*    if (dbcontextholder.get() != null) {
      system.out.println("线程名："+thread.currentthread().getname()+":"+dbcontextholder.get());
      return dbcontextholder.get();
    } else {
      system.out.println("未匹配到指定数据库,默认切换到master");
      return dbtypeenum.master;
    }*/
    //return dbcontextholder.get();
  }

}

6. 增加aop切面

@aspect
@component
@order(0)//配置注解优先级，优于事物注解@transactional先进行数据源切换，
//不然在事物中进行数据源切换无效
public class datasourceaop {

  @pointcut(/*"!@annotation(com.csc.portal.annotation.master) " +
      "&& (execution(* com.csc.portal.service..*.select*(..)) " +
      "|| execution(* com.csc.portal.service..*.get*(..))"+*/
      " @annotation(com.csc.portal.annotation.slave)")
  public void readpointcut() {

  }


  @pointcut("@annotation(com.csc.portal.annotation.master) " //+
     /* "|| execution(* com.csc.portal.service..*.insert*(..)) " +
      "|| execution(* com.csc.portal.service..*.add*(..)) " +
      "|| execution(* com.csc.portal.service..*.update*(..)) " +
      "|| execution(* com.csc.portal.service..*.edit*(..)) " +
      "|| execution(* com.csc.portal.service..*.delete*(..)) " +
      "|| execution(* com.csc.portal.service..*.remove*(..))"*/)
  public void writepointcut() {

  }

  @before("readpointcut()")
  public void read() {
    //获取拦截类
    dbcontextholder.slave();
    system.out.println(thread.currentthread().getname()+dbcontextholder.get());
  }

  @before("writepointcut()")
  public void write() {
    //获取拦截类
/*    string classname = pjp.gettarget().getclass().getname();
    system.out.println("当前线程"+thread.currentthread().getname()+" 拦截类为：" + classname);

    //获取拦截的方法名
    methodsignature msig = (methodsignature) pjp.getsignature();
    method currentmethod = null;
    try {
      currentmethod = pjp.gettarget().getclass().getmethod(msig.getname(), msig.getparametertypes());
    } catch (nosuchmethodexception e) {
      e.printstacktrace();
    }
    string methodname = currentmethod.getname();
    system.out.println("拦截方法名为：" + methodname);*/
    dbcontextholder.master();
    system.out.println(thread.currentthread().getname()+dbcontextholder.get());
  }  
}

6. 实际应用

1. 在service层方法前增加注解@master表示使用主库，进行增删改的操作使用主库。
2. 在service层方法前增加注解@slave表示使用从库，进行查的操作使用从库，默认使用从库，可不配置。
3. @ transactional注解加到service层，增加了@transactional注解后，启用事务后，一个事务内部的connection是复用的，所以就算aop切了数据源字符串，但是数据源并不会被真正修改。所以@transactional注解不要写在controller层，不然在service层也切换不了数据源。
4. @transactional与@master可同时使用，已经配置@master注解的优先级较高，先切换数据源后执行事务。
   

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