Learn from the beginning Spring-1.4 inject beans through a constructor

In this chapter we introduce the injection of beans through a constructor.

1. How does life a bean?

(1) Create a class

Package Com.raylee.my_new_spring.my_new_spring.ch01.topic_1_2;public class Song {private String Name;public song ( String name) {this.name = name;} Public Song () {} @Overridepublic String toString () {return "the Song:" + Name;}}

(2) Configuring 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.xsdhttp://www.springframework.org/schema/context Http://www.springframework.org/schema/context /spring-context-3.1.xsdhttp://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/ Spring-tx-3.1.xsdhttp://www.springframework.org/schema/util http://www.springframework.org/schema/util/ SPRING-UTIL-3.1.XSDHTTP://WWW.SPRINGFRAMEWORK.ORG/SCHEMA/DATA/JPA http://www.springframework.org/schema/data/ Jpa/spring-jpa-1.0.xsdhttp://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 would be "/></bean></beans>

2. How do I inject beans through a constructor?

Here's an example of a chef making a cake.

(1) Create a chef class

Package Com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4;public class Chief {private Cake Cake = Null;public Chief (Cake Cake) {//Where the constructor is injected this.cake = cake;} public void Makeonecake () {System.out.println (cake.tostring ());}}

When we build the chef's objects, we pass on the objects that we need to make.

(2) Create cake class

Package Com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4;public class Cake {private final int id = index++;p rivate static int index = 0; @Overridepublic String toString () {return ' Create the Cake,its ID: ' + ID;}}

Identify the ID of each object by final

And then just print a sentence that has been created

(3) configuration file

<?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.xsdhttp://www.springframework.org/schema/context Http://www.springframework.org/schema/context /spring-context-3.1.xsdhttp://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/ Spring-tx-3.1.xsdhttp://www.springframework.org/schema/util http://www.springframework.org/schema/util/ SPRING-UTIL-3.1.XSDHTTP://WWW.SPRINGFRAMEWORK.ORG/SCHEMA/DATA/JPA http://www.springframework.org/schema/data/ Jpa/spring-jpa-1.0.xsdhttp://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 "/></bean ></beans>

Configuration files are mainly configured here through bean tags.

In the bean tag can also write Constructor-arg, here is through the constructor injection, he has two parameters, one is ref, reference one of the above bean, one is value, write the value directly

(4) Create a test class

Package Com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4;import Org.junit.test;import Org.junit.runner.runwith;import Org.springframework.beans.factory.annotation.autowired;import Org.springframework.context.applicationcontext;import org.springframework.test.context.ContextConfiguration; Import Org.springframework.test.context.junit4.SpringJUnit4ClassRunner; @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 {@ Autowiredprivate applicationcontext applicationcontext; @Testpublic void Testchief () {Chief Chief = Applicationcontext.getbean (Chief.class); Chief.makeonecake ();}}

If you are building applicationcontext alone, you can use the way I commented above, because we are here to put together multiple projects, so I'm referencing an absolute path.

Output:

Create the Cake,its id:0

3. If the class does not have a public constructor, what if a singleton class is used?

According to the code above, we add an oven, while our oven chooses a singleton mode.

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 ();} @Overridepublic String toString () {return ' use old oven ';}}

The chef then adds the oven to the tool:

Package Com.raylee.my_new_spring.my_new_spring.ch01.topic_1_4;public class Chief {private Cake Cake = Null;private Oven Oven = Null;public Chief (Cake Cake) {this.cake = Cake;} Public chief (Cake Cake, Oven Oven) {this.cake = Cake;this.oven = Oven;} public void Makeonecake () {System.out.println (oven.tostring () + cake.tostring ());}}

When configured, a factory method is specially configured for the oven, and the Factory-method is set for a single case:

<?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.xsdhttp://www.springframework.org/schema/context Http://www.springframework.org/schema/context /spring-context-3.1.xsdhttp://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/ Spring-tx-3.1.xsdhttp://www.springframework.org/schema/util http://www.springframework.org/schema/util/ SPRING-UTIL-3.1.XSDHTTP://WWW.SPRINGFRAMEWORK.ORG/SCHEMA/DATA/JPA http://www.springframework.org/schema/data/ Jpa/spring-jpa-1.0.xsdhttp://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><bean id= "oven" class= "com.raylee.my_new_spring.my_new_ Spring.ch01.topic_1_4.Oven "factory-method=" getinstance "/></beans>

Test output:

Use old Ovencreate the Cake,its id:0

Summary: This section describes how to inject beans through a constructor.

My github:https://github.com/raylee2015/my_new_spring.

Learn from the beginning Spring-1.4 inject beans through a constructor