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Spring scope学习

Posted on Edited on Changyan:

spring scope

spring scope

Spring定义的scope包含五种，singleton，prototype，request，session，global session，每种scope都有自己的使用范围以及使用场景。

singleton

Scopes a single bean definition to a single object instance per Spring IoC container.

个人理解：在Spring 的IOC容器中，全局只会存在一个对象实例。每次spring启动之后，就会生成一个，也只会有一个唯一的bean对象

prototype

Scopes a single bean definition to any number of object instances.

个人理解：有无数个对象的实例，也就是说每个上层在引用时，都是一个独立的对象

request

Scopes a single bean definition to the lifecycle of a single HTTP request; that is each and every HTTP request will have its own instance of a bean created off the back of a single bean definition. Only valid in the context of a web-aware Spring ApplicationContext

个人理解：在每个http请求的生成周期内，使用同一个对象的实例，不同的http之间使用的对象都是不同的实例。只有在使用了spring的ApplicationContext的上下文才有效

session

Scopes a single bean definition to the lifecycle of a HTTP Session，Only valid in the context of a web-aware Spring ApplicationContext

个人理解：在同一个session的生命周期内，使用同一个对象的实例

global session

Scopes a single bean definition to the lifecycle of a global HTTP Session. Typically only valid when used in a portlet context. Only valid in the context of a web-aware Spring ApplicationContext

个人理解：在同一个全局session的生命周期内，使用同一个对象的实例，跟上面的session的区别在于global，也就是全局，例如使用redis等分布式session的场景。

实例解读

为了方便更好的理解上面的内容，我们通过一个例子，来对不同范围下的bean进行一个测试

测试类图：

类图

VehicleController：请求入口，用于验证不同情况下的结果输出

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@RestController
public class VehicleController {

    @Resource
    private TruckManager truckManager;

    @Resource
    private CarManager carManager;

    @GetMapping
    public void getRun(@RequestParam("type") int type) {
        if (type==1) {
            carManager.doRun();
        } else {
            truckManager.doRun();
        }
    }

}

CarManager：调用WheelsManager，不做赋值

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@Component
@Slf4j
public class CarManagerImpl implements CarManager {
    @Resource
    private WheelsManager wheelsManager;

    @Override
    public void doRun() {
        log.info("CarManagerImpl doRun  {}",wheelsManager.getWheelsCount());
    }
}

TruckManager：调用WheelsManager，给wheelsCount赋值为4

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@Component
@Slf4j
public class TruckManagerImpl implements TruckManager {

    @Resource
    private WheelsManager wheelsManager;

    @Override
    public void doRun() {
        wheelsManager.setWheelsCount(4);
        log.info("TruckManagerImpl doRun  {}", wheelsManager.getWheelsCount());
    }
}

WheelsManager：内部包含属性wheelsCount，并且提供get和set

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@Component
public class WheelsManagerImpl implements WheelsManager {

    private Integer wheelsCount;

    @Override
    public Integer getWheelsCount() {
        return wheelsCount;
    }

    public void setWheelsCount(Integer wheelCount)  {
        wheelsCount = wheelCount;
    }
}

测试方法

通过更改bean的scope的范围，接口调用分别传入1，2，来判断各种情况下wheelsCount的结果

singleton

验证不同bean，引入相同bean的场景

请求顺序：type = 1 → type = 2 → type = 1

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2022-03-20 11:08:27.204  INFO 31046 --- [  restartedMain] c.iotxing.blog.test.TestDemoApplication  : TestDemoApplication main 启动成功
2022-03-20 11:08:32.526  INFO 31046 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring DispatcherServlet 'dispatcherServlet'
2022-03-20 11:08:32.526  INFO 31046 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
2022-03-20 11:08:32.527  INFO 31046 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 1 ms
2022-03-20 11:08:32.552  INFO 31046 --- [nio-8080-exec-1] c.i.b.test.manager.impl.CarManagerImpl   : CarManagerImpl doRun  null
2022-03-20 11:08:43.003  INFO 31046 --- [nio-8080-exec-3] c.i.b.t.manager.impl.TruckManagerImpl    : TruckManagerImpl doRun  4
2022-03-20 11:08:49.842  INFO 31046 --- [nio-8080-exec-5] c.i.b.test.manager.impl.CarManagerImpl   : CarManagerImpl doRun  4

可以看出，在第一次调用时，因为wheelsCount没有赋值，所以打印出来的结果是null，第二次调用时，truckManager赋值了4，第三次调用时，carManager打印出来的也是4（上一次调用truckManager赋值的结果）

结论：全局范围内，正常方式注入的bean只有一个实例，因此如果bean存在属性，不同的请求之间都是的更改都是可见的，属于线程不安全的场景。如果bean中没有属性，只有逻辑，也就不存在安不安全的问题了。

prototype

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@Component
@Scope("prototype")
public class WheelsManagerImpl implements WheelsManager {

    private Integer wheelsCount;

    @Override
    public Integer getWheelsCount() {
        return wheelsCount;
    }

    public void setWheelsCount(Integer wheelCount)  {

        wheelsCount = wheelCount;

    }
}

spring默认的scope是singleton，更改为prototype的话，需要我们手动指定对应的scope

验证不同bean，引入相同bean的场景

请求顺序：type = 1 → type = 2 → type = 1

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2022-03-20 11:31:07.252  INFO 31888 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring DispatcherServlet 'dispatcherServlet'
2022-03-20 11:31:07.252  INFO 31888 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
2022-03-20 11:31:07.253  INFO 31888 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 1 ms
2022-03-20 11:31:07.278  INFO 31888 --- [nio-8080-exec-1] c.i.b.test.manager.impl.CarManagerImpl   : CarManagerImpl doRun  null
2022-03-20 11:31:16.509  INFO 31888 --- [nio-8080-exec-3] c.i.b.t.manager.impl.TruckManagerImpl    : TruckManagerImpl doRun  4
2022-03-20 11:31:21.201  INFO 31888 --- [nio-8080-exec-5] c.i.b.test.manager.impl.CarManagerImpl   : CarManagerImpl doRun  null

可以发现更改了scope之后，CarManager和TruckManager在初始化的时候，各自都创建了一个WheelsManager的实例出来

验证同一个bean，不同请求下的使用场景

针对单个CarManager，我们做一下改造，看一下prototype对单个bean的情况下，效果是怎么样的

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@Component
@Slf4j
public class CarManagerImpl implements CarManager {
    @Resource
    private WheelsManager wheelsManager;

    @Override
    public void doRun() {
        log.info("CarManagerImpl doRun  {}",wheelsManager.getWheelsCount());
        addPreWheel();
        addWholeWheel();
    }

    public void addPreWheel(){
        wheelsManager.setWheelsCount(wheelsManager.getWheelsCount()+2);
        log.info("CarManagerImpl addPreWheel  {}",wheelsManager.getWheelsCount());
    }

    public void addWholeWheel(){
        wheelsManager.setWheelsCount(wheelsManager.getWheelsCount()+10);
        log.info("CarManagerImpl addWholeWheel  {}",wheelsManager.getWheelsCount());
    }

}
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@Component
@Slf4j
public class TruckManagerImpl implements TruckManager {

    @Resource
    private WheelsManager wheelsManager;

    @Override
    public void doRun() {
        wheelsManager.setWheelsCount(wheelsManager.getWheelsCount()+4);
        log.info("TruckManagerImpl doRun  {}", wheelsManager.getWheelsCount());
    }
}

上面我们增加了两个方法，调用addPreWheel的时候，会给wheelsCount+2，调用WholeWheel的时候，会给wheelsCount+10，我们验证下分多次调用时候的结果

验证顺序: type = 1 → type = 1 → type = 2

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2022-03-20 11:52:56.917  INFO 32882 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 1 ms
2022-03-20 11:52:56.944  INFO 32882 --- [nio-8080-exec-1] c.i.b.test.manager.impl.CarManagerImpl   : CarManagerImpl doRun  0
2022-03-20 11:52:56.944  INFO 32882 --- [nio-8080-exec-1] c.i.b.test.manager.impl.CarManagerImpl   : CarManagerImpl addPreWheel  2
2022-03-20 11:52:56.944  INFO 32882 --- [nio-8080-exec-1] c.i.b.test.manager.impl.CarManagerImpl   : CarManagerImpl addWholeWheel  12
2022-03-20 11:52:58.922  INFO 32882 --- [nio-8080-exec-3] c.i.b.test.manager.impl.CarManagerImpl   : CarManagerImpl doRun  12
2022-03-20 11:52:58.926  INFO 32882 --- [nio-8080-exec-3] c.i.b.test.manager.impl.CarManagerImpl   : CarManagerImpl addPreWheel  14
2022-03-20 11:52:58.926  INFO 32882 --- [nio-8080-exec-3] c.i.b.test.manager.impl.CarManagerImpl   : CarManagerImpl addWholeWheel  24
2022-03-20 11:53:01.678  INFO 32882 --- [nio-8080-exec-5] c.i.b.t.manager.impl.TruckManagerImpl    : TruckManagerImpl doRun  4

可以发现，相同的bean在不同的请求时候，使用的是同一个对象，因此第二次请求时候的值是在第一次的基础上累加的，不同的bean在使用时，使用的是不同的对象，因此TruckManager的初始值是4

结论：spring启动时，对于不同的类依赖的相同的bean，注入的时候是注入的同一个bean对象的不同实例。

其它

由于request，session和global session对验证起来要求较多，并且实际中这种场景我接触不多，因此不做专门的测试了