为什么spring构造注入的优点推荐使用构造器注入

来源：蜘蛛抓取(WebSpider) 时间：2017-02-19 09:45 标签： spring 构造函数注入
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Spring（54）
这一章节我们来介绍一下通过构造器注入Bean。1.怎样声明一个Bean？（1）创建类package com.raylee.my_new_spring.my_new_spring.ch01.topic_1_2;
public class Song {
public Song(String name) {
this.name =
public Song() {
public String toString() {
return &the song:& +
（2）配置XML&?xml version=&1.0& encoding=&UTF-8&?&
&beans xmlns=&http://www.springframework.org/schema/beans&
xmlns:context=&http://www.springframework.org/schema/context&
xmlns:xsi=&http://www.w3.org/2001/XMLSchema-instance& xmlns:tx=&http://www.springframework.org/schema/tx&
xmlns:aop=&http://www.springframework.org/schema/aop&
xsi:schemaLocation=&
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsd
http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.1.xsd
http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.0.xsd
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd&&
&bean id=&song&
class=&com.raylee.my_new_spring.my_new_spring.ch01.topic_1_2.Song&&
&constructor-arg value=&there will be& /&
2.怎样通过构造器注入Bean？下面以厨师制作蛋糕为例子。（1）创建厨师类package com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4;
public class Chief {
private Cake cake =
public Chief(Cake cake) {//构造器注入的地方
this.cake =
public void makeOneCake() {
System.out.println(cake.toString());
在构建厨师的对象时，我们把需要制作的蛋糕的对象也传进去。（2）创建蛋糕类package com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4;
public class Cake {
private final int id = index++;
private static int index = 0;
public String toString() {
return &create the cake,its id:& +
通过final来标识每一个对象的id然后创建之后只是打印一句已经创建即可（3）配置文件&?xml version=&1.0& encoding=&UTF-8&?&
&beans xmlns=&http://www.springframework.org/schema/beans&
xmlns:context=&http://www.springframework.org/schema/context&
xmlns:xsi=&http://www.w3.org/2001/XMLSchema-instance& xmlns:tx=&http://www.springframework.org/schema/tx&
xmlns:aop=&http://www.springframework.org/schema/aop&
xsi:schemaLocation=&
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsd
http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.1.xsd
http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.0.xsd
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd&&
&bean id=&cake&
class=&com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4.Cake& /&
&bean id=&chief&
class=&com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4.Chief&&
&constructor-arg ref=&cake& /&
配置文件这里主要通过Bean标签来配置在Bean标签里面还可以写入constructor-arg，这里就是通过构造器注入，他里面有两个参数，一个是ref，引用上面某个bean，一个是value，直接写入值（4）创建测试类package com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4;
import org.junit.T
import org.junit.runner.RunW
import org.springframework.beans.factory.annotation.A
import org.springframework.context.ApplicationC
import org.springframework.test.context.ContextC
import org.springframework.test.context.junit4.SpringJUnit4ClassR
@RunWith(SpringJUnit4ClassRunner.class)
// @ContextConfiguration(locations = {
// &classpath:ApplicationContext-test.xml& })
@ContextConfiguration(locations = {
&/com/raylee/my_new_spring/my_new_spring/ch01/topic_1_4/ApplicationContext-test.xml& })
public class ChiefTest {
@Autowired
private ApplicationContext applicationC
public void testChief() {
Chief chief = applicationContext.getBean(Chief.class);
chief.makeOneCake();
如果是单独的建立ApplicationContext，可以使用我上面注释的方式，由于我们这里是多项目放在一起，因此我引用的是绝对路径。输出：create the cake,its id:03.如果类没有公开的构造器，如果使用单例的类？根据上面的代码，我们补充一个烤炉，而我们这个烤炉选择单例模式。package com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4;
public class Oven {
private Oven() {
public static Oven getInstance() {
return new Oven();
public String toString() {
return &use old oven&;
然后厨师那里加上烤炉这个工具：package com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4;
public class Chief {
private Cake cake =
private Oven oven =
public Chief(Cake cake) {
this.cake =
public Chief(Cake cake, Oven oven) {
this.cake =
this.oven =
public void makeOneCake() {
System.out.println(oven.toString() + cake.toString());
配置的时候特别为烤炉配置一个工厂方法，factory-method就是为了单例这种情况来设置的：&?xml version=&1.0& encoding=&UTF-8&?&
&beans xmlns=&http://www.springframework.org/schema/beans&
xmlns:context=&http://www.springframework.org/schema/context&
xmlns:xsi=&http://www.w3.org/2001/XMLSchema-instance& xmlns:tx=&http://www.springframework.org/schema/tx&
xmlns:aop=&http://www.springframework.org/schema/aop&
xsi:schemaLocation=&
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsd
http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.1.xsd
http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.0.xsd
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd&&
&bean id=&cake&
class=&com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4.Cake& /&
&bean id=&chief&
class=&com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4.Chief&&
&constructor-arg ref=&cake& /&
&constructor-arg ref=&oven& /&
&bean id=&oven&
class=&com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4.Oven&
factory-method=&getInstance& /&
测试输出：use old ovencreate the cake,its id:0&总结：这一章节介绍了如何通过构造器注入Bean。目录：&&我的github：&&
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