Spring當(dāng)中aop:scoped-proxy 的用法

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當(dāng)把生命周期短的bean（比如下例中的MyBean）注入到生命周期長的bean（比如下例中的SingletonBean）時(shí)，我們必須做特殊處理，比如加<aop:scoped-proxy>來修飾短生命周期的bean。為什么？其實(shí)也好理解。比如下例中的生命周期長的bean （SingletonBean）的類型是Singleton，還沒有用戶訪問時(shí)，在最初的時(shí)刻就建立了，而且只建立一次。這時(shí)它的一個(gè)屬性myBean卻要急著指向另外一個(gè)session類型的bean（com.MyBean），而com.MyBean的生命周期短（只有當(dāng)有用戶訪問時(shí)，它才被生成）?，F(xiàn)在處于初始階段，還沒有用戶上網(wǎng)呢，所以com.MyBean的真正對(duì)象還沒有生成呢。所以<aop:scoped-proxy>的意思就是讓myBean這個(gè)屬性指向com.MyBean的一個(gè)代理對(duì)象。（該代理對(duì)象擁有和com.MyBean完全相同的public接口。調(diào)用代理對(duì)象方法時(shí)，代理對(duì)象會(huì)從Session范圍內(nèi)獲取真正的com.MyBean對(duì)象，調(diào)用其方法）。下例中如果去除<aop:scoped-proxy /> 會(huì)報(bào)以下的錯(cuò)誤：Error creating bean with name 'myBean': Scope 'session' is not active for the current thread; consider defining a scoped proxy for this bean，注意在做以下實(shí)驗(yàn)時(shí)，要導(dǎo)入包c(diǎn)glib-nodep-2.1_3.jar。


例 2.4.1

    <bean id="myBean" class="com.MyBean" scope="session">
         <aop:scoped-proxy />
    </bean>  
  
    <bean id="singletonBean" class="com.SingletonBean">
        <property name="myBean">
            <ref bean="myBean" />
        </property>
    </bean>





package com;
public class MyBean implements IMyBean{
    private int count;
    public int getCount() {
        return count;
    }
    public void setCount(int count) {
        this.count = count;
    }
    public void increment()
    {
        count ++;
    }
}



package com;
public interface IMyBean {
    public void increment();
    public int getCount();
}



package com;
public class SingletonBean {
    private MyBean myBean;
    public int getCount() {
        return myBean.getCount();
    }
    public void increment() {
        myBean.increment();
    }
    public void setMyBean(MyBean myBean) {
        this.myBean = myBean;
    }
}





package com;
import javax.annotation.Resource;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import org.springframework.stereotype.Controller;
import org.springframework.stereotype.Service;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.support.RequestContextUtils;
import service.interfac.ILoginService;

@Controller
public class HelloWorldController {
    private ILoginService loginServic;

    private IMyBean myBean;
    @RequestMapping("/helloa")
    public ModelAndView helloWorld(HttpServletRequest request, HttpServletResponse response,
            HttpSession sesssion) {
        ServletContext sc=RequestContextUtils.getWebApplicationContext(request).getServletContext();
        WebApplicationContext wac=WebApplicationContextUtils.getRequiredWebApplicationContext(sc);
        ILoginService loginServic=(ILoginService)wac.getBean("loginService");
        SingletonBean singletonBean=(SingletonBean)wac.getBean("singletonBean");
 //       loginServic.login();
        singletonBean.increment();
        System.out.println("myBean.getCount() "+singletonBean.getCount());
        System.out.println("after loginServic.login()");
        return new ModelAndView("/helloq", "message", "你好");
    }
}


輸出結(jié)果：（在同一個(gè)瀏覽器中反復(fù)執(zhí)行就是以下結(jié)果，換一個(gè)瀏覽器數(shù)據(jù)重新向上加）

myBean.getCount() 1
after loginServic.login()
myBean.getCount() 2
after loginServic.login()
myBean.getCount() 3
after loginServic.login()