@lazy注入

最新推荐文章于 2024-04-20 14:30:00 发布

stevenxyy

最新推荐文章于 2024-04-20 14:30:00 发布

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文章标签： dubbo java spring boot

本文链接：https://blog.youkuaiyun.com/stevenxyy/article/details/129770656

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该文章展示了一个使用SpringBoot和ApacheDubbo的示例提供者应用，其中`DemoService`被两次@Autowired，一次不带@Lazy，一次带有@Lazy。@Lazy注解使得依赖在实际使用时才会初始化，而不是在应用启动时。文章通过代码示例解释了@Lazy注解的工作原理和效果。

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Licensed to the Apache Software Foundation (ASF) under one or more
contributor license agreements. See the NOTICE file distributed with
this work for additional information regarding copyright ownership.
The ASF licenses this file to You under the Apache License, Version 2.0
(the “License”); you may not use this file except in compliance with
the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an “AS IS” BASIS,
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*/

package org.apache.dubbo.springboot.demo.provider;

import org.apache.dubbo.config.spring.context.annotation.EnableDubbo;
import org.apache.dubbo.springboot.demo.DemoService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Lazy;

@SpringBootApplication
@EnableDubbo
public class ProviderApplication implements ApplicationRunner {

@Autowired
private DemoService demoService1;


@Lazy
@Autowired
private DemoService demoService2;
public static void main(String[] args) {
    SpringApplication.run(ProviderApplication.class, args);
}

@Override
public void run(final ApplicationArguments args) throws Exception {
    System.out.println("(demoService1 == demoService2) = " + (demoService1 == demoService2));
    //false
    //原因: lazy注入是注入的一个lazy代理, 代理中的target指向spring getBean, 从而实现了在调用属性的方法时才获取bean
    // 源码: lazyLookup ?  buildLazyResourceProxy ()
    // ps0: lazy注入不是不注入, 是不注入不就空指针了吗
    // ps1: 是加了一个代理, 没有什么是加一层代理解决不了的, 比如 @RefreshScope 热更新, @lazy注入依赖
    // ps2: 这里的lazy是用在 autowired依赖注入, 当用在@compont上时,bean肯定是同一个, 不用加一层, 看上去也会懒生成(最终要看源码的意思)
    // ps3: api getbean肯定还是同一个
}

}