mybatis多个plugins的执行顺序解析-编程学习网

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&amp;characterEncoding=utf-8&amp;useSSL=false&amp;useJDBCCompliantTimezoneShift=true&amp;useLegacyDatetimeCode=false&amp;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？