Spring--循环依赖的解决方案--实例

简介

说明

        本文用实例介绍如何解决Spring的循环依赖问题。

相关网址

Spring--循环依赖导致启动失败_IT利刃出鞘的博客-博客_springboot 配置循环依赖

公共代码

package com.example.controller;

import com.example.tmp.A;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {
    @Autowired
    private A a;

    @GetMapping("/test1")
    public String test1() {
        return a.getTest();
    }
}

方案1. Feild注入单例（@AutoWired）

代码

package com.example.tmp;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
 
@Component
public class A {
    @Autowired
    private B b;
 
    private String name = "Tony";
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public String getTest() {
        return b.getAge().toString() + name;
    }
}

package com.example.tmp;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
 
@Component
public class B {
    @Autowired
    private A a;
 
    private Integer age = 20;
 
    public Integer getAge() {
        return age;
    }
 
    public void setAge(Integer age) {
        this.age = age;
    }

}

测试

启动不报错。

postman访问：​​http://localhost:8080/test1​​

后端结果：不报错

postman结果: 20Tony

方案2. 构造器注入+@Lazy

延迟加载：在注入依赖时，先注入代理对象，当首次使用时再创建对象完成注入。

代码

package com.example.tmp;

import org.springframework.context.annotation.Lazy;
import org.springframework.stereotype.Component;
 
@Component
public class A {
    private B b;

    public A(@Lazy B b) {
        this.b = b;
    }
 
    private String name = "Tony";
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public String getTest() {
        return b.getAge().toString() + name;
    }
}

package com.example.tmp;

import org.springframework.context.annotation.Lazy;
import org.springframework.stereotype.Component;
 
@Component
public class B {
    private A a;

    public B(@Lazy A a) {
        this.a = a;
    }
 
    private Integer age = 20;
 
    public Integer getAge() {
        return age;
    }
 
    public void setAge(Integer age) {
        this.age = age;
    }

}

测试

启动不报错。

postman访问：​​http://localhost:8080/test1​​

后端结果：不报错

postman结果: 20Tony

方案3. Setter/Field注入单例

代码

package com.example.tmp;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
 
@Component
public class A {
    private B b;
 
    private String name = "Tony";
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public String getTest() {
        return b.getAge().toString() + name;
    }

    public B getB() {
        return b;
    }

    @Autowired
    public void setB(B b) {
        this.b = b;
    }
}

package com.example.tmp;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
 
@Component
public class B {
    private A a;

    private Integer age = 20;
 
    public Integer getAge() {
        return age;
    }
 
    public void setAge(Integer age) {
        this.age = age;
    }

    public A getA() {
        return a;
    }

    @Autowired
    public void setA(A a) {
        this.a = a;
    }
}

测试 

启动不报错。

postman访问：​​http://localhost:8080/test1​​

后端结果：不报错

postman结果: 20Tony

方案4. @PostConstruct

代码

package com.example.tmp;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;

@Component
public class A {
    @Autowired
    private B b;

    @PostConstruct
    public void init() {
        b.setA(this);
    }
 
    private String name = "Tony";
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public String getTest() {
        return b.getAge().toString() + name;
    }
}

package com.example.tmp;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
 
@Component
public class B {
    @Autowired
    private A a;

    private Integer age = 20;
 
    public Integer getAge() {
        return age;
    }
 
    public void setAge(Integer age) {
        this.age = age;
    }

    public A getA() {
        return a;
    }

    public void setA(A a) {
        this.a = a;
    }
}

测试 

启动不报错。

postman访问：​​http://localhost:8080/test1​​

后端结果：不报错

postman结果: 20Tony

方案5. 实现ApplicationContextAware与InitializingBean

代码 

package com.example.tmp;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;

@Component
public class A implements ApplicationContextAware, InitializingBean {
    private B b;

    private ApplicationContext context;

    private String name = "Tony";
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public String getTest() {
        return b.getAge().toString() + name;
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        this.b = context.getBean(B.class);
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.context = applicationContext;
    }
}

package com.example.tmp;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
 
@Component
public class B {
    @Autowired
    private A a;

    private Integer age = 20;
 
    public Integer getAge() {
        return age;
    }
 
    public void setAge(Integer age) {
        this.age = age;
    }
}

测试 

启动不报错。

postman访问：​​http://localhost:8080/test1​​

后端结果：不报错

postman结果: 20Tony