简介
说明
本文用实例介绍如何解决Spring的循环依赖问题(SpringBoot2.6之前的版本)。
相关网址
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. 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
注意
SpringBoot2.6版本开始,已默认禁止了循环依赖,必须要加个配置才能启用循环依赖:
application.yml添加如下配置:
spring main allow-circular-references: true
请先
!