SpringBoot 通过自定义 Mybatis 拦截器，实现 SQL 的改写

1、拦截器应用场景：

（1）分页，如com.github.pagehelper的分页插件实现。

（2）拦截sql做日志监控；

（3）统一对某些sql进行统一条件拼接，类似于分页。

2、研究初衷：

（1）做什么：通过拦截器对查询的 sql 进行改写， 让 pageHelper 执行的是改写后的 sql。

（2）怎样做：由于分页使用的是 Pagehelper ，其内部机制也是通过拦截器实现的。基于 MyBatis 拦截器链的加载机制，后加载的会先执行，也就是说我们

自定义的拦截器，必须加载在 Pagehelper之后。

3、相关配置类实现：

（1）MySqlInterceptor 类：

package spcommon.config;

import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.mapping.*;
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 java.util.Properties;

/**
 * 自定义 MyBatis 拦截器
 */
@Intercepts({@Signature(type = Executor.class, method = "query",
        args = {MappedStatement.class, Object.class, RowBounds.class,ResultHandler.class})})
public class MySqlInterceptor implements Interceptor {

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

    /**
     * intercept 方法用来对拦截的sql进行具体的操作
     * @param invocation
     * @return
     * @throws Throwable
     */
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        logger.info("执行intercept方法：{}", invocation.toString());

        Object[] args = invocation.getArgs();
        MappedStatement ms = (MappedStatement) args[0];
        Object parameterObject = args[1];

        // id为执行的mapper方法的全路径名，如com.mapper.UserMapper
        String id = ms.getId();

        // sql语句类型 select、delete、insert、update
        String sqlCommandType = ms.getSqlCommandType().toString();

        // 仅拦截 select 查询
        //if (!sqlCommandType.equals(SqlCommandType.SELECT.toString())) {
        //    return invocation.proceed();
        //}
        
        BoundSql boundSql = ms.getBoundSql(parameterObject);
        String origSql = boundSql.getSql();
        logger.info("原始SQL: {}", origSql);

        // 组装新的 sql
        String newSql = origSql + " limit 1";

        // 重新new一个查询语句对象
        BoundSql newBoundSql = new BoundSql(ms.getConfiguration(), newSql,
                boundSql.getParameterMappings(), boundSql.getParameterObject());

        // 把新的查询放到statement里
        MappedStatement newMs = newMappedStatement(ms, new BoundSqlSqlSource(newBoundSql));
        for (ParameterMapping mapping : boundSql.getParameterMappings()) {
            String prop = mapping.getProperty();
            if (boundSql.hasAdditionalParameter(prop)) {
                newBoundSql.setAdditionalParameter(prop, boundSql.getAdditionalParameter(prop));
            }
        }

        Object[] queryArgs = invocation.getArgs();
        queryArgs[0] = newMs;

        logger.info("改写的SQL: {}", newSql);

        return invocation.proceed();
    }

    /**
     * 定义一个内部辅助类，作用是包装 SQL
     */
    class BoundSqlSqlSource implements SqlSource {
        private BoundSql boundSql;
        public BoundSqlSqlSource(BoundSql boundSql) {
            this.boundSql = boundSql;
        }
        public BoundSql getBoundSql(Object parameterObject) {
            return boundSql;
        }

    }

    private MappedStatement newMappedStatement (MappedStatement ms, SqlSource newSqlSource) {
        MappedStatement.Builder builder = new
                MappedStatement.Builder(ms.getConfiguration(), ms.getId(), newSqlSource, ms.getSqlCommandType());
        builder.resource(ms.getResource());
        builder.fetchSize(ms.getFetchSize());
        builder.statementType(ms.getStatementType());
        builder.keyGenerator(ms.getKeyGenerator());
        if (ms.getKeyProperties() != null && ms.getKeyProperties().length > 0) {
            builder.keyProperty(ms.getKeyProperties()[0]);
        }
        builder.timeout(ms.getTimeout());
        builder.parameterMap(ms.getParameterMap());
        builder.resultMaps(ms.getResultMaps());
        builder.resultSetType(ms.getResultSetType());
        builder.cache(ms.getCache());
        builder.flushCacheRequired(ms.isFlushCacheRequired());
        builder.useCache(ms.isUseCache());
        return builder.build();
    }

    @Override
    public Object plugin(Object target) {
        logger.info("plugin方法：{}", target);

        if (target instanceof Executor) {
            return Plugin.wrap(target, this);
        }
        return target;

    }

    @Override
    public void setProperties(Properties properties) {
        // 获取属性
        // String value1 = properties.getProperty("prop1");
        logger.info("properties方法：{}", properties.toString());
    }

}

（2）MyBatisConfig 类：

package spcommon.config;

import com.github.pagehelper.autoconfigure.PageHelperAutoConfiguration;
import org.apache.ibatis.session.SqlSessionFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.AutoConfigureAfter;
import org.springframework.context.annotation.Configuration;

import javax.annotation.PostConstruct;
import java.util.List;
import java.util.Properties;

@Configuration
@AutoConfigureAfter(PageHelperAutoConfiguration.class)
public class MyBatisConfig {

    @Autowired
    private List<SqlSessionFactory> sqlSessionFactoryList;

    @PostConstruct
    public void addMySqlInterceptor() {
        MySqlInterceptor interceptor = new MySqlInterceptor();
        for (SqlSessionFactory sqlSessionFactory : sqlSessionFactoryList) {

            // 添加自定义属性
//            Properties properties = new Properties();
//            properties.setProperty("prop1", "value1");
//            interceptor.setProperties(properties);
            sqlSessionFactory.getConfiguration().addInterceptor(interceptor);

        }
    }

}

（3）在 resources 目录下创建META-INF目录下，在 META-INF 目录下创建 spring.factories 文件，文件内容如下：

# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=
com.github.pagehelper.autoconfigure.PageHelperAutoConfiguration,
xxx.xxx.MyBatisConfig  

4、测试总结

在同时使用 PageHelper 和 自定义拦截器时，以上配置可解决 spring boot 在使用 pagehelper-spring-boot-starter 后 ，自定义拦截器失效的问题。

 参考链接：

https://www.jianshu.com/p/59e28ad9e738

https://www.jianshu.com/p/0a72bb1f6a21