mybatis多个plugins的执行顺序解析

作者：子衿_青青时间：2021-12-09 18:53:27　

一、前言

在mybatis官网中，有插件一说 mybatis plugins 如果同时有多个插件，那么他们的执行顺序是怎样的？

二、准备工作、代码准备

1、项目结构

2、TestDAO

public interface TestDAO {
Test selectById(Integer id);

default void testDefaultMethod(){
System.out.println("===调用接口中的默认方法，用来验证MapperProxy中的isDefaultMethod方法===");
}
}

3、Test

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Test {
private Integer id;

private String name;
}

4、ExamplePlugin

@Intercepts({@Signature(
type= Executor.class, method = "query", args={MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}
),
@Signature(
type = ParameterHandler.class, method = "setParameters", args = {PreparedStatement.class}
),
@Signature(
type = ResultSetHandler.class, method = "handleResultSets", args = {Statement.class}
),
@Signature(
type = StatementHandler.class, method = "prepare", args = {Connection.class, Integer.class}
)
})
public class ExamplePlugin implements Interceptor {
@Override
public Object intercept(Invocation invocation) throws Throwable {
System.out.println("==== ExamplePlugin 开始搞事情：" + invocation.getMethod().getName() + " ====");
return invocation.proceed();
}

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

@Override
public void setProperties(Properties properties) {

}
}

5、SecondExamplePlugin

@Intercepts({@Signature(
type= Executor.class, method = "query", args={MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}
),
@Signature(
type = ParameterHandler.class, method = "setParameters", args = {PreparedStatement.class}
),
@Signature(
type = ResultSetHandler.class, method = "handleResultSets", args = {Statement.class}
),
@Signature(
type = StatementHandler.class, method = "prepare", args = {Connection.class, Integer.class}
)
})
public class SecondExamplePlugin implements Interceptor {
@Override
public Object intercept(Invocation invocation) throws Throwable {
System.out.println("==== SecondExamplePlugin 开始搞事情：" + invocation.getMethod().getName() + " ====");
return invocation.proceed();
}

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

@Override
public void setProperties(Properties properties) {

}
}

6、Main

public class Main {

public static SqlSession getSqlSession() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
return sqlSessionFactory.openSession();
}

public static void main(String[] args) throws IOException {
TestDAO testDAO = getSqlSession().getMapper(TestDAO.class);
Test test = testDAO.selectById(1);

// testDAO.testDefaultMethod();

//类文件是缓存在java虚拟机中，我们将类文件打印到文件中，便于查看
// generateProxyFile("F:/TestDAOProxy.class");
}

private static void generateProxyFile(String path){
byte[] classFile = ProxyGenerator.generateProxyClass("$Proxy0", new Class<?>[]{TestDAO.class});

try(FileOutputStream fos = new FileOutputStream(path)) {
fos.write(classFile);
fos.flush();
System.out.println("代理类class文件写入成功");
} catch (Exception e) {
System.out.println("写文件错误");
}
}
}

7、 TestMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.me.mybatis.dao.TestDAO">
<resultMap id="testMap" type="com.me.mybatis.domain.Test">
<result property="id" column="id" />
<result property="name" column="name" />
</resultMap>

<sql id="allColumn">
id, name
</sql>

<select id="selectById" resultMap="testMap">
SELECT <include refid="allColumn"/>
FROM test
WHERE id = #{id}
</select>

</mapper>

8、mybatis-confi.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<plugins>
<plugin interceptor="com.me.mybatis.plugin.ExamplePlugin">
<property name="someProperty" value="200" />
</plugin>
<plugin interceptor="com.me.mybatis.plugin.SecondExamplePlugin">
<property name="someProperty" value="200" />
</plugin>
</plugins>

<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mybatis_test?useUnicode=true&characterEncoding=utf-8&useSSL=false&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC"/>
<property name="username" value="root"/>
<property name="password" value="NewPwd@123"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="mappers/TestMapper.xml"/>
</mappers>
</configuration>

9、POM

<?xml version="1.0" encoding="UTF-8"?>
<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.me</groupId>
<artifactId>mybatis-test</artifactId>
<version>1.0-SNAPSHOT</version>

<properties>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>

<dependencies>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.4.6</version>
</dependency>

<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.16.14</version>
</dependency>

<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
</dependency>

<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.12</version>
</dependency>
</dependencies>

</project>

三、开始探索

1、运行结果

==== SecondExamplePlugin 开始搞事情：query ====
==== ExamplePlugin 开始搞事情：query ====
==== SecondExamplePlugin 开始搞事情：prepare ====
==== ExamplePlugin 开始搞事情：prepare ====
==== SecondExamplePlugin 开始搞事情：setParameters ====
==== ExamplePlugin 开始搞事情：setParameters ====
==== SecondExamplePlugin 开始搞事情：handleResultSets ====
==== ExamplePlugin 开始搞事情：handleResultSets ====

2、疑问：为什么是这样的顺序？

和我们在mybatis-config.xml文件中的顺序相反，为什么？