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How to analyze the principle of Mapper in Java Mybatis, many novices are not very clear about this. In order to help you solve this problem, the following editor will explain it in detail. People with this need can come and learn. I hope you can get something.

Prepare the 1.pom file org.mybatis mybatis 3.4.5 mysql mysql-connector-java 5.1.6 runtime junit junit 4.12 Test log4j log4j 1.2.12 org.projectlombok lombok 1.18.2 provided 2.user Class-Database

3. Entity class @ Getter@Setter@ToString@NoArgsConstructorpublic class user {private int id; private String username; private String password;} 4.dao layer public interface userDao {List findAll ();} 5.Mapper file select * from user

Core profile

Core code

Import dao.userDao;import mode.user;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import java.io.IOException;import java.io.InputStream;import java.util.List;public class TestMapper {public static void main (String [] args) throws IOException {/ / load the core configuration file InputStream resourceAsStream = Resources.getResourceAsStream ("SqlMapConfig.xml") / / get sqlSession factory object SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder () .build (resourceAsStream); / / get sqlSession object SqlSession sqlSession = sqlSessionFactory.openSession (); / / execute sql statement userDao mapper = sqlSession.getMapper (userDao.class); List userList = mapper.findAll (); / / print result System.out.println (userList) / / release resource sqlSession.close ();}} Source code analysis 1. Breakpoint

two。 View the source code

DefaultSqlSession:

Configuration:

This is the Configuration class. We mainly look at the getMapper () method.

MapperRegistry:

Key code: mapperProxyFactory.newInstance (sqlSession)

MapperProxyFactory:

The MapperProxy object is returned

MapperProxy:

Source code:

/ / Source code recreated from a .class file by IntelliJ IDEA// (powered by FernFlower decompiler) / / package org.apache.ibatis.binding;import java.io.Serializable;import java.lang.invoke.MethodHandles.Lookup;import java.lang.reflect.Constructor;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.util.Map;import org.apache.ibatis.lang.UsesJava7;import org.apache.ibatis.reflection.ExceptionUtil;import org.apache.ibatis.session.SqlSession Public class MapperProxy implements InvocationHandler, Serializable {private static final long serialVersionUID =-6424540398559729838L; private final SqlSession sqlSession; private final Class mapperInterface; private final Map methodCache; public MapperProxy (SqlSession sqlSession, Class mapperInterface, Map methodCache) {this.sqlSession = sqlSession; this.mapperInterface = mapperInterface; this.methodCache = methodCache } public Object invoke (Object proxy, Method method, Object [] args) throws Throwable {try {if (Object.class.equals (method.getDeclaringClass () {return method.invoke (this, args);} if (this.isDefaultMethod (method)) {return this.invokeDefaultMethod (proxy, method, args) } catch (Throwable var5) {throw ExceptionUtil.unwrapThrowable (var5);} MapperMethod mapperMethod = this.cachedMapperMethod (method); return mapperMethod.execute (this.sqlSession, args);} private MapperMethod cachedMapperMethod (Method method) {MapperMethod mapperMethod = (MapperMethod) this.methodCache.get (method) If (mapperMethod = = null) {mapperMethod = new MapperMethod (this.mapperInterface, method, this.sqlSession.getConfiguration ()); this.methodCache.put (method, mapperMethod);} return mapperMethod;} @ UsesJava7 private Object invokeDefaultMethod (Object proxy, Method method, Object [] args) throws Throwable {Constructor constructor = Lookup.class.getDeclaredConstructor (Class.class, Integer.TYPE) If (! constructor.isAccessible ()) {constructor.setAccessible (true);} Class declaringClass = method.getDeclaringClass (); return ((Lookup) constructor.newInstance (declaringClass, 15)) .unreflect Special (method, declaringClass) .bindTo (proxy) .invokeWithArguments (args);} private boolean isDefaultMethod (Method method) {return (method.getModifiers () & 1033) = = 1 & method.getDeclaringClass (). IsInterface ();}}

As you can see in the invoke method, if we call a method in Object without doing any processing, call it directly, otherwise execute:

MapperMethod.execute (this.sqlSession, args)

MapperMethod:

Classified reflection of SQL statements in MapperMethod

In MapperProxyFactory, use the dynamic proxy of JDK to generate the proxy class of the Mapper interface

The method in MapperMethod is called by dynamic processor MapperProxy to handle and execute SQL.

Finally, it is decided to call the corresponding method in SqlSession to execute SQL in MapperMethod according to the returned value of the executed method.

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