Spring第八篇：容器中bean對象的創建順序

　　一、無依賴bean的創建和銷毀順序

　　Spring的org.springframework.beans.factory.DisposableBean接口中存在destroy()方法，當我們的調用容器的close()方法會調用所有bean的destroy()方法來做相應的處理。

　　創建無依賴bean的class文件。

public class NoDependBean {

    public static class Bean1 implements DisposableBean{

        public Bean1() {
            System.out.println(this.getClass() + "constructor!");
        }

        @Override
        public void destroy() throws Exception {
            System.out.println(this.getClass() + "destroy()");
        }
    }

    public static class  Bean2 implements DisposableBean{

        public Bean2() {
            System.out.println(this.getClass() + "constructor!");
        }

        @Override
        public void destroy() throws Exception {
            System.out.println(this.getClass() + "destroy()");
        }
    }

    public static class Bean3 implements DisposableBean{

        public Bean3(){
            System.out.println(this.getClass() + "constructor!");
        }

        @Override
        public void destroy() throws Exception {
            System.out.println(this.getClass() + "destroy()");
        }
    }

}

　　test方法運行結果：從運行結果可以看出，無依賴bean創建順序以xml文件中的配置順序一致，銷毀順序則是xml配置文件的倒敘。

class com.java.spring01.demo6.NoDependBean$Bean3constructor!
class com.java.spring01.demo6.NoDependBean$Bean2constructor!
class com.java.spring01.demo6.NoDependBean$Bean1constructor!
class com.java.spring01.demo6.NoDependBean$Bean1destroy()
class com.java.spring01.demo6.NoDependBean$Bean2destroy()
class com.java.spring01.demo6.NoDependBean$Bean3destroy()

　　二、通過構造器強依賴的bean創建和銷毀

　　class文件

public class StrongDependBean {
    public static class Bean1 implements DisposableBean{

        public Bean1() {
            System.out.println(this.getClass() + "constructor!");
        }

        @Override
        public void destroy() throws Exception {
            System.out.println(this.getClass() + "destroy()");
        }
    }

    public static class  Bean2 implements DisposableBean{
        private Bean1 bean1;
        public Bean2(Bean1 bean1) {
            this.bean1 = bean1;
            System.out.println(this.getClass() + "constructor!");
        }

        public Bean2() {
        }

        @Override
        public void destroy() throws Exception {
            System.out.println(this.getClass() + "destroy()");
        }
    }

    public static class Bean3 implements DisposableBean {

        private Bean2 bean2;

        public Bean3(Bean2 bean2){
            this.bean2 = bean2;
            System.out.println(this.getClass() + "constructor!");
        }

        public Bean3() {
        }

        @Override
        public void destroy() throws Exception {
            System.out.println(this.getClass() + "destroy()");
        }
    }

}

　　bean.xml文件增加配置

<!--強依賴對象創建-->
    <bean id = "bean3" class="com.java.spring01.demo6.StrongDependBean.Bean3" autowire="constructor"/>
    <bean id = "bean2" class="com.java.spring01.demo6.StrongDependBean.Bean2" autowire="constructor"/>
    <bean id = "bean1" class="com.java.spring01.demo6.StrongDependBean.Bean1"/>

　　test方法運行結果

class com.java.spring01.demo6.StrongDependBean$Bean1constructor!
class com.java.spring01.demo6.StrongDependBean$Bean2constructor!
class com.java.spring01.demo6.StrongDependBean$Bean3constructor!
class com.java.spring01.demo6.StrongDependBean$Bean3destroy()
class com.java.spring01.demo6.StrongDependBean$Bean2destroy()
class com.java.spring01.demo6.StrongDependBean$Bean1destroy()

　　強依賴的創建順序同依賴一致，銷毀同依賴關系相反。

　　三、使用depend-on干擾bean的創建和銷毀

<bean id="bean1" class="" depend-on="bean2,bean3; bean4" />

　　depend-on用來定義創建當前的bean之前，需要先創建好哪些bean對象。銷毀的時候會先此處id的bean對象，然后再去銷毀依賴的bean對象。

　　在無依賴的bean.xml中添加depend-on屬性指定創建屬性，來查看bean的創建和銷毀。修改bean.xml文件增加depend-on屬性。

<bean id = "bean3" class="com.java.spring01.demo6.NoDependBean.Bean3" depends-on="bean1 bean2"/>
    <bean id = "bean2" class="com.java.spring01.demo6.NoDependBean.Bean2"/>
    <bean id = "bean1" class="com.java.spring01.demo6.NoDependBean.Bean1"/>

　　運行test方法，查看運行結果。

class com.java.spring01.demo6.NoDependBean$Bean1constructor!
class com.java.spring01.demo6.NoDependBean$Bean2constructor!
class com.java.spring01.demo6.NoDependBean$Bean3constructor!
class com.java.spring01.demo6.NoDependBean$Bean3destroy()
class com.java.spring01.demo6.NoDependBean$Bean2destroy()
class com.java.spring01.demo6.NoDependBean$Bean1destroy()

總結

1. 無依賴的bean創建順序和定義的順序一致，銷毀順序剛好相反

2. 通過構造器強依賴的bean，會先創建構造器參數中對應的bean，然后才會創建當前bean，銷毀順序剛好相反

3. depend-on可以指定檔期bean依賴的bean，通過這個可以確保depend-on指定的bean在當前bean創建之前先創建好，銷毀順序剛好相反

4. bean的銷毀順序和bean創建的順序相反