Mybatis的Mapper接口UserMapper
1 package com.safin.Mapper;
2
3 import com.safin.Pojo.User;
4
5 import java.util.List;
6
7 public interface UserMapper {
8 int insertUser(User user);
9 User getUser(Long id);
10 List<User> findUser(String userName);
11 }
我使用的jdk版本是12的，在java.lang.reflect包下的ProxyGenerator是生成代理类的工具，这是用来生成运行时代理类（$proxy为前缀）。注意其中一个属性，这是用来保存那些构建的代理类的开关saveGeneratedFiles，其默认赋值是false，当saveGeneratedFiles的值为true时，那些运行时生成的代理类将会以.class文件保存下来。
1 /** debugging flag for saving generated class files */ 2 private static final boolean saveGeneratedFiles = 3 java.security.AccessController.doPrivileged( 4 new GetBooleanAction( 5 "jdk.proxy.ProxyGenerator.saveGeneratedFiles")).booleanValue();
在测试主函数开始第一句先添加如下代码，把saveGeneratedFiles的开关打开。jdk12中的"jdk.proxy.ProxyGenerator.saveGeneratedFiles"这个值与jdk8中的稍微不同，在jdk8的这个值是"sun.misc.ProxyGenerator.saveGeneratedFiles"。说起misc，他的全称应该是minimal instruction set computer，最小指令集计算机是一种处理器体系结构，具有非常少量的基本操作和相应的操作码。
还有jdk8与jdk12的Proxy的实现发生了很大的变化，以后有时间再去研究研究。
1 System.getProperties().put("jdk.proxy.ProxyGenerator.saveGeneratedFiles", "true");
测试的Main函数如下：
1 public static void main(String[] args) throws IOException {
2 SqlSession sqlSession = null;
3 System.getProperties().put("jdk.proxy.ProxyGenerator.saveGeneratedFiles", "true"); // 打开保存生成的代理类
4
5 try {
6 sqlSession = SqlSessionFactoryUtil.openSqlSession();
7 UserMapper userMapper = (UserMapper)sqlSession.getMapper(UserMapper.class);
8 User user = null;
9 user = userMapper.getUser(30L);
10 sqlSession.commit();
11 } catch (Exception var9) {
12 System.err.println(var9.getMessage());
13 sqlSession.rollback();
14 } finally {
15 if (sqlSession != null) {
16 sqlSession.close();
17 }
18
19 }
20
21 }
运行后保存了许多代理类，找出与Mapper有关的的代理类$proxy，代理类经过IDEA的反编译后，代码如下：
1 //
2 // Source code recreated from a .class file by IntelliJ IDEA
3 // (powered by Fernflower decompiler)
4 //
5
6 package com.sun.proxy;
7
8 import com.safin.Mapper.UserMapper;
9 import com.safin.Pojo.User;
10 import java.lang.reflect.InvocationHandler;
11 import java.lang.reflect.Method;
12 import java.lang.reflect.Proxy;
13 import java.lang.reflect.UndeclaredThrowableException;
14 import java.util.List;
15
16 public final class $Proxy19 extends Proxy implements UserMapper {
17 private static Method m1;
18 private static Method m3;
19 private static Method m4;
20 private static Method m5;
21 private static Method m2;
22 private static Method m0;
23
24 public $Proxy19(InvocationHandler var1) throws {
25 super(var1); // 传入构造方法的参数是实现了InvocationHandler接口的MapperProxy
26 }
27
28 public final boolean equals(Object var1) throws {
29 try {
30 return (Boolean)super.h.invoke(this, m1, new Object[]{var1}); // 从InvocationHandler的invoke方法
31 } catch (RuntimeException | Error var3) {
32 throw var3;
33 } catch (Throwable var4) {
34 throw new UndeclaredThrowableException(var4);
35 }
36 }
37
38 public final User getUser(Long var1) throws {
39 try {
40 return (User)super.h.invoke(this, m3, new Object[]{var1});
41 } catch (RuntimeException | Error var3) {
42 throw var3;
43 } catch (Throwable var4) {
44 throw new UndeclaredThrowableException(var4);
45 }
46 }
47
48 public final int insertUser(User var1) throws {
49 try {
50 return (Integer)super.h.invoke(this, m4, new Object[]{var1});
51 } catch (RuntimeException | Error var3) {
52 throw var3;
53 } catch (Throwable var4) {
54 throw new UndeclaredThrowableException(var4);
55 }
56 }
57
58 public final List findUser(String var1) throws {
59 try {
60 return (List)super.h.invoke(this, m5, new Object[]{var1});
61 } catch (RuntimeException | Error var3) {
62 throw var3;
63 } catch (Throwable var4) {
64 throw new UndeclaredThrowableException(var4);
65 }
66 }
67
68 public final String toString() throws {
69 try {
70 return (String)super.h.invoke(this, m2, (Object[])null);
71 } catch (RuntimeException | Error var2) {
72 throw var2;
73 } catch (Throwable var3) {
74 throw new UndeclaredThrowableException(var3);
75 }
76 }
77
78 public final int hashCode() throws {
79 try {
80 return (Integer)super.h.invoke(this, m0, (Object[])null);
81 } catch (RuntimeException | Error var2) {
82 throw var2;
83 } catch (Throwable var3) {
84 throw new UndeclaredThrowableException(var3);
85 }
86 }
87
88 static { // 拿到了反射API的Method
89 try {
90 m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
91 m3 = Class.forName("com.safin.Mapper.UserMapper").getMethod("getUser", Class.forName("java.lang.Long"));
92 m4 = Class.forName("com.safin.Mapper.UserMapper").getMethod("insertUser", Class.forName("com.safin.Pojo.User"));
93 m5 = Class.forName("com.safin.Mapper.UserMapper").getMethod("findUser", Class.forName("java.lang.String"));
94 m2 = Class.forName("java.lang.Object").getMethod("toString");
95 m0 = Class.forName("java.lang.Object").getMethod("hashCode");
96 } catch (NoSuchMethodException var2) {
97 throw new NoSuchMethodError(var2.getMessage());
98 } catch (ClassNotFoundException var3) {
99 throw new NoClassDefFoundError(var3.getMessage());
100 }
101 }
102 }
可以看见生成的代理类 $Proxy19 继承了 Proxy 类，实现了Mybatis的 UserMapper 接口，调用InvocationHandler的invoke方法来利用MapperMethod来对sqlSession的操作。
原文地址：https://www.cnblogs.com/magic-sea/p/11229237.html
时间： 2024-10-03 01:34:10