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This article focuses on "what are the three ways to inject Spring member objects?". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn what are the three ways of injecting Spring member objects.

When a class needs to call a member object, and the member object is also a class object managed by the container class, you can use dependency injection to create a member object. Let the container class help you create member objects.

Front:

Container class AppConfig

Import org.springframework.context.annotation.ComponentScan;import org.springframework.context.annotation.Configuration;@Configuration@ComponentScanpublic class AppConfig {}

Create an interface Hello

Public interface Hello {void HelloWorld ();}

Create a class HelloImpl1 that implements the interface Hello. And is hosted by the container.

Import org.springframework.stereotype.Component;@Componentpublic class HelloImpl1 implements Hello {@ Override public void HelloWorld () {System.out.println ("HelloWorld1");} one, @ Autowired comments

Annotate the declared member variable with @ Autowires. Let the container help create the object. The member variable must also be managed by the container class.

Create a MyHello class with Hello member objects in it. As follows:

Import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Component;@Componentpublic class MyHello {@ Autowired Hello h; void say () {h.HelloWorld ();}}

If you run say () without @ Autowired, you will get an error.

To test:

Import org.springframework.context.ApplicationContext;import org.springframework.context.annotation.AnnotationConfigApplicationContext;public class Test {public static void main (String [] args) {ApplicationContext ac = new AnnotationConfigApplicationContext (AppConfig.class); MyHello mh = ac.getBean ("myHello", MyHello.class); mh.say ();}}

Running result:

If the member object is an interface and there are multiple implementation classes. You need to use @ Qualifier or @ Primary annotations.

Create a class that implements the Hello interface.

Import org.springframework.stereotype.Component;@Componentpublic class HelloImol2 implements Hello {@ Override public void HelloWorld () {System.out.println ("HelloWorld2");}}

At this point, the Hello interface has two implementation classes.

Run the Test class again to report an error. Because there is a conflict with the calling class.

There are two solutions.

@ Qualifier

Add @ Qualifier (value= "id name") under @ Autowired. The id name defaults to the class name and the first letter is lowercase. You want to specify which class in the implementation interface is called.

Such as the above solution:

Import org.springframework.beans.factory.annotation.Autowired;import org.springframework.beans.factory.annotation.Qualifier;import org.springframework.stereotype.Component;@Componentpublic class MyHello {@ Autowired @ Qualifier (value= "helloImpl1") / / add this note Hello h; void say () {h.HelloWorld ();}}

@ Primary

Add the @ Primary annotation to one of the multiple implementation interface objects you want to use

I want to run HelloImpl1 through Hello. Add @ Primary comment to HelloImpl:

Import org.springframework.context.annotation.Primary;import org.springframework.stereotype.Component;@Component@Primarypublic class HelloImpl1 implements Hello {@ Override public void HelloWorld () {System.out.println ("HelloWorld1");}}

The Test class ran successfully

2. @ Resource comment

Add @ Resource (name= "id name") to the member object with the name of the class you want to call the class implemented in this interface with a lowercase initials.

Then the above MyHello class can be written as:

Import org.springframework.stereotype.Component;import javax.annotation.Resource;@Componentpublic class MyHello {@ Resource (name= "helloImpl1") Hello h; void say () {h.HelloWorld ();}}

Run the Test class

@ Inject and @ Named annotations

Using these two annotations requires importing coordinates. Join in pom.xml

Javax.inject javax.inject 1

The two annotations are used together on the need to create member objects. Where @ Named ("id name") id is the name of the class you want to call the class implemented in this interface with a lowercase initials.

Then the above MyHello class can be modified to:

Import org.springframework.stereotype.Component;import javax.inject.Inject;import javax.inject.Named;@Componentpublic class MyHello {@ Inject @ Named ("helloImpl1") Hello h; void say () {h.HelloWorld ()}}

Continue to run the Test class, you can still run successfully

The above can also implement the dependency injection of the set method, and you need to ensure that the passed parameters are managed by the container.

At this point, I believe you have a deeper understanding of "what are the three ways to inject Spring member objects?". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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