mybatis通过插件方式实现读写分离

原理：通过自定义mybatis插件，拦截Executor的update和query方法，检查sql中有select就用读的库，其它的用写的库（如果有调用存储过程就另当别论了）

@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 }) })

@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 RWDataSourceMybatisPlugin implements Interceptor {

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

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

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

        Object[] objects = invocation.getArgs();
        MappedStatement ms = (MappedStatement) objects[0];

        RWDataSourceType dataSourceType = null;

        if ((dataSourceType = 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)) {
                    dataSourceType = RWDataSourceType.WRITE;
                } else {
                    BoundSql boundSql = ms.getSqlSource().getBoundSql(objects[1]);
                    String sql = boundSql.getSql().toLowerCase().replaceAll("[\t\n\r]", " ");
                    if (sql.matches(REGEX)) {
                        dataSourceType = RWDataSourceType.WRITE;
                    } else {
                        dataSourceType = RWDataSourceType.READ;
                    }
                }
            } else {
                dataSourceType = RWDataSourceType.WRITE;
            }
            cacheMap.put(ms.getId(), dataSourceType);
        }
        // 修改当前线程要选择的数据源的key
        RWDataSourceHolder.putDataSource(dataSourceType);

        return invocation.proceed();
    }

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

附：

MyBatis 允许你在已映射语句执行过程中的某一点进行拦截调用。默认情况下，MyBatis 允许使用插件来拦截的方法调用包括：

• Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed)
• ParameterHandler (getParameterObject, setParameters)
• ResultSetHandler (handleResultSets, handleOutputParameters)
• StatementHandler (prepare, parameterize, batch, update, query)

　　spring boot加载插件方式

    @Bean
    public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
        SqlSessionFactoryBean fb = new SqlSessionFactoryBean();
        fb.setDataSource(dataSource);
        fb.setMapperLocations(
                new PathMatchingResourcePatternResolver().getResources(env.getProperty("mybatis.mapper-locations")));
        PageHelper pageHelper = new PageHelper();
        Properties props = new Properties();
        props.setProperty("reasonable", "true");
        props.setProperty("supportMethodsArguments", "true");
        props.setProperty("returnPageInfo", "check");
        props.setProperty("params", "count=countSql");
        pageHelper.setProperties(props);
        fb.setPlugins(new Interceptor[] { pageHelper, new MybatisSqlInterceptor() });
        return fb.getObject();
    }

随便开发的一个记录sql的插件

package com.qmtt.config;

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

import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.mapping.BoundSql;
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;

@Intercepts({ @Signature(type = StatementHandler.class, method = "prepare", args = { Connection.class, Integer.class }) })
public class MybatisSqlInterceptor implements Interceptor {

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

        StatementHandler statementHandler = (StatementHandler) invocation.getTarget();
        BoundSql boundSql = statementHandler.getBoundSql();
        String sql = boundSql.getSql();
        System.out.println(sql);
        return invocation.proceed();
    }

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

    @Override
    public void setProperties(Properties properties) {
        // String dialect = properties.getProperty("dialect");
    }
}