使用 Spring（AOP？）实现 Java 接口

Question

我有几个简单的 getter 和 setter 接口以及一些其他方法来从文件系统读取和写入。直接使用 Java 代码，我可以编写一个 "invocation handler" 并用它来实例化所有这些接口的对象（我没有尝试过，但我认为它可以完成）。

我想知道是否可以使用 Spring 来做同样的事情。

下面的代码实现了给定的接口。如您所见，相同的调用处理程序可用于任何接口。

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class AOPTester {

    public static void main(String[] args) {
        InvocationHandler handler = new MyInvocationHandler();
        AnyInterface proxy = (AnyInterface) Proxy.newProxyInstance(
                                    AnyInterface.class.getClassLoader(),
                                    new Class[] { AnyInterface.class },
                                    handler);

        proxy.sayHello();

    }

}

interface AnyInterface {
    public void sayHello();
}

class MyInvocationHandler implements InvocationHandler{

    public Object invoke(Object proxy, Method method, Object[] args)
            throws Throwable {
        System.out.println("Hello!");

        return null;
    }
}

Answer 1

以下配置应该适合您（我使用了您的类但我将它们移到了不同的包中只是为了使代码更具可读性）。我使用 spring 上下文对您使用的工厂方法 newProxyInstance() 执行相同的调用。

<beans xmlns="http://www.springframework.org/schema/beans"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
 xmlns:aop="http://www.springframework.org/schema/aop"
 xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
        http://www.springframework.org/schema/aop 
        http://www.springframework.org/schema/aop/spring-aop-3.2.xsd">

    <bean id="pojoInvocationHandler" class="com.someco.PojoInvocationHandler"></bean>

    <bean id="AnyInterfaceClass" class="java.lang.Class" factory-method="forName">
        <constructor-arg value="com.someco.AnyInterface"/>
    </bean>

    <bean id="anyInterface" class="java.lang.reflect.Proxy" factory-method="newProxyInstance">
        <constructor-arg>
            <bean 
                factory-bean="AnyInterfaceClass" 
                factory-method="getClassLoader" />
        </constructor-arg>
        <constructor-arg>
            <list>
                <ref bean="AnyInterfaceClass" />
            </list>
        </constructor-arg>
        <constructor-arg ref="pojoInvocationHandler"/>
    </bean>
</beans>

代理测试器：

package com.someco;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.someco.AnyInterface;

public class ProxyTester {

    public static void main(String[] args) {
        ApplicationContext contex = new ClassPathXmlApplicationContext("application-context.xml"); 
        AnyInterface tester = (AnyInterface) contex.getBean("anyInterface"); 
        tester.sayHello();

        /* Implemented with the previous code */
//      callProxy();
    }

    /**
     * @deprecated
     * explanation of why function was deprecated, if possible include what 
     * should be used.
     */
    @Deprecated
    public static void callProxy() {
        InvocationHandler handler = new PojoInvocationHandler();
        AnyInterface proxy = (AnyInterface) Proxy.newProxyInstance(
                                    AnyInterface.class.getClassLoader(),
                                    new Class[] { AnyInterface.class },
                                    handler);
        proxy.sayHello();
    }

}

PojoInvocationHandler:

package com.someco;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class PojoInvocationHandler implements InvocationHandler{

    public Object invoke(Object proxy, Method method, Object[] args)
            throws Throwable {
        System.out.println("Hello!");

        return null;
    }
}

任意接口：

package com.someco;

public interface AnyInterface {
    public void sayHello();
}

基本pom.xml:

<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.someco</groupId>
    <artifactId>proxy-tester</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>main</name>
    <url>http://maven.apache.org</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <spring.version>3.0.5.RELEASE</spring.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>${spring.version}</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>${spring.version}</version>
        </dependency>
    </dependencies>
</project>

Answer 2

实际上有一种使用 ProxyFactoryBean Spring 的简洁方法。在下面的示例中，这个 class 是在没有目标 bean 的情况下初始化的。创建的对象没有任何转发请求的目标，但它可以像 Java.

中的任何其他代理一样实现任何接口

当然，如果您尝试在传递给 MethodInterceptor 的 invoke 方法的调用对象上调用 proceed 方法，您将得到 NullPointerException。

更好的应用-context.xml:

<beans xmlns="http://www.springframework.org/schema/beans"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
 xmlns:aop="http://www.springframework.org/schema/aop"
 xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
        http://www.springframework.org/schema/aop 
        http://www.springframework.org/schema/aop/spring-aop-3.2.xsd">

    <bean id="goodbyeMethodInterceptor" class="com.someco.GoodbyeMethodInterceptor" />

    <bean name="goodbyeProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
        <property name="interfaces">
            <list>
                <value>com.someco.AnyInterface</value>
            </list>
        </property>
        <property name="interceptorNames">
            <list>
                <value>goodbyeMethodInterceptor</value>
            </list>
        </property>
    </bean>
</beans>

再见方法拦截器：

package com.someco;

import org.aopalliance.intercept.MethodInvocation;

public class GoodbyeMethodInterceptor implements org.aopalliance.intercept.MethodInterceptor {

    public Object invoke(MethodInvocation invocation) throws Throwable {
        System.out.println("Goodbye");

        return null;
    }

}

代理测试器：

package com.someco;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.someco.AnyInterface;

public class ProxyTester {

    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("better-application-context.xml"); 
        AnyInterface tester = (AnyInterface) context.getBean("goodbyeProxy");
        tester.sayHello();
    }
}

任何接口：

package com.someco;

public interface AnyInterface {
    public void sayHello();
}

基本pom.xml:

<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.someco</groupId>
    <artifactId>proxy-tester</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>main</name>
    <url>http://maven.apache.org</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <spring.version>3.0.5.RELEASE</spring.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>${spring.version}</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>${spring.version}</version>
        </dependency>
    </dependencies>
</project>

使用 Spring（AOP？）实现 Java 接口

Implements a Java Interface using Spring (AOP?)

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