Spring入門學習手冊 2：怎麼用註解來DI/IOC

EatherToo發表於2019-03-02
Spring

目錄

一、如果使用註解的話，在配置檔案中應該做什麼？

在beans標籤後加上一個

<context:annotation-config/>
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標籤來宣告將要使用註解就可以了。

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
    
    <!--在此處加上此標籤-->
    <context:annotation-config/>
    <bean name="c" class="com.learn.springDemo.Category">
        <property name="name" value="Eather"></property>
        <property name="id" value="12345"></property>
    </bean>
    <bean name="p" class="com.learn.springDemo.Product">
        <property name="name" value="a product"></property>
        <property name="id" value="1008611"></property>

        <!--將下面這行註釋掉，因為程式碼中將使用自動裝配來將categroy例項注入product-->
        <!--<property name="category" ref="c"></property>-->

    </bean>

</beans>
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二、註解應該怎麼用？

如果是使用@Autowired註解的話，可以加在兩個地方前面。

屬性前面 以及 setter方法前面。

如下程式碼:

package com.learn.springDemo;

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

public class Product {
    private int id;
    private String name;

    //加在這個地方
    @Autowired
    private Category category;

    public void setId(int id) {
        this.id = id;
    }

    public void setName(String name) {
        this.name = name;
    }

    //加在這個地方
    @Autowired
    public void setCategory(Category category) {
        this.category = category;
    }

    public int getId() {
        return this.id;
    }

    public String getName() {
        return this.name;
    }

    public Category getCategory() {
        return this.category;
    }
}

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在這裡必須要import org.springframework.beans.factory.annotation.Autowired;

執行結果：

a product`s id is 1008611 and its category name is Eather
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三、注入同一個類的不同例項應該怎麼辦？

上一篇筆記 裡提到了 xml裡面可以寫多個相同的bean嗎 這個問題，也就是注入同一個類的不同例項應該怎麼辦？在使用xml配置時很簡單，改一下name就行。

此時就可以使用@Resource註解

先改一下xml配置檔案

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">

    <!--在此處加上此標籤-->
    <context:annotation-config/>
    <bean name="c" class="com.learn.springDemo.Category">
        <property name="name" value="Eather"></property>
        <property name="id" value="12345"></property>
    </bean>
    <bean name="cc" class="com.learn.springDemo.Category">
        <property name="name" value="David"></property>
        <property name="id" value="10086"></property>
    </bean>
    <bean name="p" class="com.learn.springDemo.Product">
        <property name="name" value="a product"></property>
        <property name="id" value="1008611"></property>

        <!--將下面這行註釋掉-->
        <!--<property name="category" ref="c"></property>-->

    </bean>

</beans>
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註解應該加在屬性的前面

package com.learn.springDemo;

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

import javax.annotation.Resource;

public class Product {
    private int id;
    private String name;

    @Resource(name = "c")
    private Category category;

    @Resource(name = "cc")
    private Category category1;

    public void setId(int id) {
        this.id = id;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setCategory(Category category) {
        this.category = category;
    }

    public void setCategory1(Category category1) {
        this.category1 = category1;
    }

    public int getId() {
        return this.id;
    }

    public String getName() {
        return this.name;
    }

    public Category getCategory() {
        return this.category;
    }

    public Category getCategory1() {
        return category1;
    }
}
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測試程式碼：

package com.learn.springTest;

import com.learn.springDemo.Product;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test {
    public static void main(String args[]) {
        ApplicationContext ac = new ClassPathXmlApplicationContext(new String[]{"applicationContext.xml"});


        Product p = (Product) ac.getBean("p");

        System.out.println(p.getName() + "`s id is " + p.getId() + " and its category name is "  + p.getCategory().getName() + " and " + p.getCategory1().getName());

    }

}
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執行結果：

a product`s id is 1008611 and its category name is Eather and David
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四、xml配置檔案裡可不可以 bean 也不寫？

上述例子都是對 注入物件行為 的註解，對於bean物件本身的使用可不可以也用註解的方式進行，而不寫到配置檔案中呢？

答案當然是可以，修改一下配置檔案，去掉所有beans和bean標籤，加上

<context:component-scan base-package="com.learn.springDemo"/>
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base-package 用來指定要掃描的包。

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">

    <!--在此處加上此標籤-->
    <context:component-scan base-package="com.learn.springDemo" />

</beans>
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類定義程式碼是：

package com.learn.springDemo;

import org.springframework.stereotype.Component;

@Component("c")
public class Category {
    private int id;
    private String name = "我是一個Category";

    public int getId() {
        return this.id;
    }

    public String getName() {
        return this.name;
    }

    public void setId(int id) {
        this.id = id;
    }

    public void setName(String name) {
        this.name = name;
    }
}



package com.learn.springDemo;

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


@Component("p")
public class Product {
    private int id;
    private String name = "我是一個product";

    @Autowired
    private Category category;

    public void setId(int id) {
        this.id = id;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setCategory(Category category) {
        this.category = category;
    }


    public int getId() {
        return this.id;
    }

    public String getName() {
        return this.name;
    }

    public Category getCategory() {
        return this.category;
    }
}
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測試程式碼是：

package com.learn.springTest;

import com.learn.springDemo.Product;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Test {
    public static void main(String args[]) {
        ApplicationContext ac = new ClassPathXmlApplicationContext(new String[]{"applicationContext.xml"});


        Product p = (Product) ac.getBean("p");

        System.out.println("product 名字是 " + p.getName() + " category 名字是 "  + p.getCategory().getName());

    }

}
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執行結果是：

product 名字是 我是一個product category 名字是 我是一個Category
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至於前面的第三個問題應該怎麼解決，暫時我也不知道，可能這個問題沒有太大的意義吧！

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