動態代理

public class Main {
    public static void main(String[] args) {
        final ProxyMapper mapper = (ProxyMapper) Proxy.newProxyInstance(Main.class.getClassLoader(), new Class[]{ProxyMapper.class}, new InvocationHandler() {
            @Override
            public Object invoke(Object o, Method method, Object[] objects) throws
 
 Throwable {
                return 1;
            }
        });
        mapper.select();
    }

    interface ProxyMapper {
        int select();
    }
}

代理類內容

final class $Proxy0 extends Proxy implements PorxyMapper {
    private static Method m1;
    private static Method m2;
    private
 
 static Method m3;
    private static Method m0;

    public $Proxy0(InvocationHandler var1) throws  {
        super(var1);
    }

    public final boolean equals(Object var1) throws  {
        try {
            return (Boolean)super.h.invoke(this, m1, new Object[]{var1});
        } catch (RuntimeException | Error var3) {
            
 
throw var3;
        } catch (Throwable var4) {
            throw new UndeclaredThrowableException(var4);
        }
    }

    public final String toString() throws  {
        try {
            return (String)super.h.invoke(this, m2, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final int select() throws  {
        try {
            return (Integer)super.h.invoke(this, m3, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final int hashCode() throws  {
        try {
            return (Integer)super.h.invoke(this, m0, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    static {
        try {
            m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
            m2 = Class.forName("java.lang.Object").getMethod("toString");
            m3 = Class.forName("com.mochasoft.nonstop.config.Main$PorxyMapper").getMethod("select");
            m0 = Class.forName("java.lang.Object").getMethod("hashCode");
        } catch (NoSuchMethodException var2) {
            throw new NoSuchMethodError(var2.getMessage());
        } catch (ClassNotFoundException var3) {
            throw new NoClassDefFoundError(var3.getMessage());
        }
    }
}

Mybatis程式碼

public class Main {
    public static void main(String[] args) {
        System.getProperties().put("jdk.proxy.ProxyGenerator.saveGeneratedFiles", "true");
        HikariDataSource dataSource = new HikariDataSource();
        TransactionFactory transactionFactory = new JdbcTransactionFactory();
        Environment environment = new Environment("development", transactionFactory, dataSource);
        Configuration configuration = new Configuration(environment);
        configuration.addMapper(ProxyMapper.class);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
        final SqlSession sqlSession = sqlSessionFactory.openSession();
        final ProxyMapper mapper = sqlSession.getMapper(ProxyMapper.class);
    }
    interface ProxyMapper {
        @Select("select * from dual")
        int select();
    }
}

建立Mapper代理類

MapperRegistry.getMapper

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
    if (mapperProxyFactory == null) {
        throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    }
    try {
        return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
        throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
}

MapperProxyFactory.newInstance

public T newInstance(SqlSession sqlSession) {
    final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
}

MapperProxy.invoke

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
        if (Object.class.equals(method.getDeclaringClass())) {
            return method.invoke(this, args);
        } else if (method.isDefault()) {
            return invokeDefaultMethod(proxy, method, args);
        }
    } catch (Throwable t) {
        throw ExceptionUtil.unwrapThrowable(t);
    }
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    return mapperMethod.execute(sqlSession, args);
}

記錄Mybatis的Mapper：

　　一般我們使用JDK動態代理的時候，會對一個介面已有的實現類進行代理，進而會進入一個誤區 => JDK動態代理會有一個介面實現類的入參。