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如何進行Java Mybatis中的Mapper原理分析，很多新手對此不是很清楚，為了幫助大家解決這個難題，下面小編將為大家詳細講解，有這方面需求的人可以來學習下，希望你能有所收獲。
<dependencies> <!--mybatis坐標--> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.4.5</version> </dependency> <!--mysql驅動坐標--> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.6</version> <scope>runtime</scope> </dependency> <!--單元測試坐標--> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> <scope>test</scope> </dependency> <!--日志坐標--> <dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>1.2.12</version> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <version>1.18.2</version> <scope>provided</scope> </dependency> </dependencies>
@Getter
@Setter
@ToString
@NoArgsConstructor
public class user {
private int id;
private String username;
private String password;
}public interface userDao {
List<user> findAll();
}<?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="dao.userDao"> <select id="findAll" resultType="mode.user"> select * from user </select> </mapper>
核心配置文件
<?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>
<!--通過properties標簽加載外部properties文件-->
<properties resource="jdbc.properties"></properties>
<!--自定義別名-->
<typeAliases>
<typeAlias type="mode.user" alias="user"></typeAlias>
</typeAliases>
<!--數據源環境-->
<environments default="developement">
<environment id="developement">
<transactionManager type="JDBC"></transactionManager>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
</dataSource>
</environment>
</environments>
<!--加載映射文件-->
<mappers>
<mapper resource="userMapper.xml"></mapper>
</mappers>
</configuration>核心代碼
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 {
//加載核心配置文件
InputStream resourceAsStream = Resources.getResourceAsStream("SqlMapConfig.xml");
//獲得sqlSession工廠對象
SqlSessionFactory sqlSessionFactory = new
SqlSessionFactoryBuilder().build(resourceAsStream);
//獲得sqlSession對象
SqlSession sqlSession = sqlSessionFactory.openSession();
//執行sql語句
userDao mapper = sqlSession.getMapper(userDao.class);
List<user> userList = mapper.findAll();
//打印結果
System.out.println(userList);
//釋放資源
sqlSession.close();
}
}
DefaultSqlSession:
Configuration:
這是Configuration 類。我們主要看getMapper()方法
MapperRegistry：
關鍵代碼:mapperProxyFactory.newInstance(sqlSession);
MapperProxyFactory:
返回的是MapperProxy 對象
MapperProxy：
源碼：
// 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<T> implements InvocationHandler, Serializable {
private static final long serialVersionUID = -6424540398559729838L;
private final SqlSession sqlSession;
private final Class<T> mapperInterface;
private final Map<Method, MapperMethod> methodCache;
public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> 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<Lookup> constructor = Lookup.class.getDeclaredConstructor(Class.class, Integer.TYPE);
if (!constructor.isAccessible()) {
constructor.setAccessible(true);
}
Class<?> declaringClass = method.getDeclaringClass();
return ((Lookup)constructor.newInstance(declaringClass, 15)).unreflectSpecial(method, declaringClass).bindTo(proxy).invokeWithArguments(args);
}
private boolean isDefaultMethod(Method method) {
return (method.getModifiers() & 1033) == 1 && method.getDeclaringClass().isInterface();
}
}
在invoke方法中可以看到,如果我們調用的是Object中的方法,不做任何處理,直接調用,否則執行:
mapperMethod.execute(this.sqlSession, args);
MapperMethod:
在MapperMethod 中對SQL語句進行分類反射
MapperProxyFactory中,使用JDK的動態代理生成Mapper接口的代理代理類
由動態處理器MapperProxy中調用MapperMethod中的方法處理執行SQL
最后,在MapperMethod中根據執行的方法返回值決定調用SqlSession中的對應方法執行SQL
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