Mybatis插件
约 891 字大约 3 分钟
Mybatis中也提供了插件的功能，虽然叫插件，但是实际上是通过拦截器（Interceptor）实现的。在MyBatis的插件模块中涉及责任链模式和JDK动态代理 --《Mybatis技术内幕（徐郡明 编著）》
在mybatis项目中通过实现 org.apache.ibatis.plugin.Interceptor接口可以定义一个拦截器，重写 intercept()方法来定义拦截器的具体操作。同时通过 @org.apache.ibatis.plugin.Intercepts和 @org.apache.ibatis.plugin.Signature注解定义需要被拦截的位置（类和方法）。常见的插件如分库分表、自动分页、数据脱敏、加密解密等等
下面以两个简单的例子，说明拦截器的具体实现
SQL耗时插件
@Intercepts({
@Signature(type = StatementHandler.class, method = "query", args = {Statement.class, ResultHandler.class}),
@Signature(type = StatementHandler.class, method = "update", args = {Statement.class}),
@Signature(type = StatementHandler.class, method = "batch", args = {Statement.class})
})
public class SqlCostTimeInterceptor implements Interceptor {
private static Logger logger = LoggerFactory.getLogger(SqlCostTimeInterceptor.class);
@Override
public Object intercept(Invocation invocation) throws Throwable {
Object target = invocation.getTarget();
long startTime = System.currentTimeMillis();
StatementHandler statementHandler = (StatementHandler) target;
try {
return invocation.proceed();
} finally {
long costTime = System.currentTimeMillis() - startTime;
BoundSql boundSql = statementHandler.getBoundSql();
String sql = boundSql.getSql();
logger.info("执行 SQL：[ {} ]执行耗时[ {} ms]", sql, costTime);
}
}
@Override
public Object plugin(Object target) {
return Plugin.wrap(target, this);
}
@Override
public void setProperties(Properties properties) {
System.out.println("插件配置的信息："+properties);
}
}<!-- MyBatis全局配置文件：mybatis-config.xml -->
<plugins>
<plugin interceptor="com.xzg.cd.a88.SqlCostTimeInterceptor">
<property name="someProperty" value="100"/>
</plugin>
</plugins>分页插件
mybatis分页的详细实现思路可参考 MyBatis分页插件PageHelper项目
实现思路如下：
- 拦截
org.apache.ibatis.executor.Executor#query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler)方法 - 获取到
rowBounds参数中的offset和limit - 获取到
MappedStatement参数中的sql语句，并根据上一步中的分页参数重新构建分页sql - 偷天换日，使用上一步生成的分页sql语句构建新的MappedStatement，替换原有
MappedStatement - 执行查询操作
代码如下
package top.sunyog.mybatis.plugins;
import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.SqlSource;
import org.apache.ibatis.plugin.Interceptor;
import org.apache.ibatis.plugin.Intercepts;
import org.apache.ibatis.plugin.Invocation;
import org.apache.ibatis.plugin.Signature;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import java.util.Properties;
@Intercepts({@Signature(type = Executor.class, method = "query"
, args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class})})
public class PageHelperInterceptor implements Interceptor {
private final int STATEMENT_ARG_INDEX = 0;
private final int PARAMETER_ARG_INDEX = 1;
private final int ROWBOUND_ARG_INDEX = 2;
@Override
public Object intercept(Invocation invocation) throws Throwable {
Object[] args = invocation.getArgs();
//获取待查sql
MappedStatement ms = (MappedStatement) args[STATEMENT_ARG_INDEX];
Object parameter = args[PARAMETER_ARG_INDEX];
BoundSql sql = ms.getBoundSql(parameter);
String sqlStr = sql.getSql().trim();
//获取分页内容
RowBounds rowBounds = (RowBounds) args[ROWBOUND_ARG_INDEX];
int limit = rowBounds.getLimit();
int offset = rowBounds.getOffset();
//重新拼接sql
StringBuffer buffer = new StringBuffer(sqlStr.length() + 100);
buffer.append("select t.* from (");
buffer.append(sqlStr);
buffer.append(") t limit ").append(offset).append(", ").append(limit);
//创建新的statement
Configuration config = ms.getConfiguration();
BoundSql newBoundSql = new BoundSql(config, buffer.toString(), sql.getParameterMappings(), parameter);
SqlSource sqlSource = o -> newBoundSql;
//按照原有ms生成新ms
MappedStatement.Builder builder = new MappedStatement.Builder(config, ms.getId(), sqlSource, ms.getSqlCommandType());
builder.resource(ms.getResource())
.fetchSize(ms.getFetchSize())
.statementType(ms.getStatementType())
.keyGenerator(ms.getKeyGenerator())
.timeout(ms.getTimeout())
.parameterMap(ms.getParameterMap())
.resultMaps(ms.getResultMaps())
.resultSetType(ms.getResultSetType())
.cache(ms.getCache())
.flushCacheRequired(ms.isFlushCacheRequired())
.useCache(ms.isUseCache());
//替换原来的ms
args[STATEMENT_ARG_INDEX] = builder.build();
//替换原来的rowBound
RowBounds newRowBounds = new RowBounds(RowBounds.NO_ROW_OFFSET, RowBounds.NO_ROW_LIMIT);
args[ROWBOUND_ARG_INDEX] = newRowBounds;
return invocation.proceed();
}
@Override
public Object plugin(Object target) {
return Interceptor.super.plugin(target);
}
@Override
public void setProperties(Properties properties) {
Interceptor.super.setProperties(properties);
}
}配置文件中添加插件配置，注意mybatis配置文件中标签的顺序
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"https://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<properties resource="mysql-env.properties">
<property name="test-key" value="test-value-c"/>
</properties>
<settings>...</settings>
<typeAliases>...</typeAliases>
<typeHandlers>...</typeHandlers>
<plugins>
<plugin interceptor="top.sunyog.mybatis.plugins.PageHelperInterceptor"/>
</plugins>
<environments>...</environments>
<mappers>...</mappers>
</configuration>测试代码如下：
private void testListPage(){
SqlSession sqlSession = MybatisAppContext.getSqlSessionFactory().openSession();
final String statement="top.sunyog.mybatis.mapper.LessonMapper.getDemos";
//调用被拦截的方法
sqlSession.select(statement, null, new RowBounds(0, 1), new ResultHandler() {
@Override
public void handleResult(ResultContext resultContext) {
Object obj = resultContext.getResultObject();
System.out.println(obj);
}
});
sqlSession.close();
}查询打印结果如下，数据库中有多条记录
TestDemo{demoId=1, demoName='测试名称', demoDesc='测试备注'}在mybatis插件中可以拦截的方法如下：
Executor类中的update()、query()、flushStatements()、commit()、rollback()、getTransaction()、close()、isClosed()方法；ParameterHandler类中的getParameterObject()、setParameters()方法；ResultSetHandler类中的handleResultSets()、handleOu飞putParameters()方法；StatementHandler类中的prepare()、parameterize()、batch()、update()、query()方法。