📅  最后修改于: 2020-11-11 07:04:43             🧑  作者: Mango
到目前为止,您已经了解了我们如何使用XML配置文件配置Spring bean。如果您对XML配置感到满意,那么实际上不需要学习如何进行基于Java的配置,因为您将使用两种可用的配置来达到相同的结果。
基于Java的配置选项使您无需XML即可编写大部分Spring配置,而借助本章中介绍的基于Java的注释很少。
用@Configuration注释一个类表示该类可以被Spring IoC容器用作bean定义的源。 @Bean注释告诉Spring使用@Bean注释的方法将返回一个对象,该对象应在Spring应用程序上下文中注册为Bean。最简单的@Configuration类如下所示-
package com.tutorialspoint;
import org.springframework.context.annotation.*;
@Configuration
public class HelloWorldConfig {
@Bean
public HelloWorld helloWorld(){
return new HelloWorld();
}
}
上面的代码将等效于以下XML配置-
在这里,方法名称用@Bean标注为bean ID,它创建并返回实际的bean。您的配置类可以具有多个@Bean的声明。一旦定义了配置类,就可以使用AnnotationConfigApplicationContext将它们加载并提供给Spring容器,如下所示-
public static void main(String[] args) {
ApplicationContext ctx = new AnnotationConfigApplicationContext(HelloWorldConfig.class);
HelloWorld helloWorld = ctx.getBean(HelloWorld.class);
helloWorld.setMessage("Hello World!");
helloWorld.getMessage();
}
您可以按如下方式加载各种配置类:
public static void main(String[] args) {
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
ctx.register(AppConfig.class, OtherConfig.class);
ctx.register(AdditionalConfig.class);
ctx.refresh();
MyService myService = ctx.getBean(MyService.class);
myService.doStuff();
}
让我们拥有一个运行良好的Eclipse IDE,并采取以下步骤来创建一个Spring应用程序:
Steps | Description |
---|---|
1 | Create a project with a name SpringExample and create a package com.tutorialspoint under the src folder in the created project. |
2 | Add required Spring libraries using Add External JARs option as explained in the Spring Hello World Example chapter. |
3 | Because you are using Java-based annotations, so you also need to add CGLIB.jar from your Java installation directory and ASM.jar library which can be downloaded from asm.ow2.org. |
4 | Create Java classes HelloWorldConfig, HelloWorld and MainApp under the com.tutorialspoint package. |
5 | The final step is to create the content of all the Java files and Bean Configuration file and run the application as explained below. |
这是HelloWorldConfig.java文件的内容
package com.tutorialspoint;
import org.springframework.context.annotation.*;
@Configuration
public class HelloWorldConfig {
@Bean
public HelloWorld helloWorld(){
return new HelloWorld();
}
}
这是HelloWorld.java文件的内容
package com.tutorialspoint;
public class HelloWorld {
private String message;
public void setMessage(String message){
this.message = message;
}
public void getMessage(){
System.out.println("Your Message : " + message);
}
}
以下是MainApp.java文件的内容
package com.tutorialspoint;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.*;
public class MainApp {
public static void main(String[] args) {
ApplicationContext ctx =
new AnnotationConfigApplicationContext(HelloWorldConfig.class);
HelloWorld helloWorld = ctx.getBean(HelloWorld.class);
helloWorld.setMessage("Hello World!");
helloWorld.getMessage();
}
}
创建完所有源文件并添加所需的其他库后,让我们运行该应用程序。您应该注意,不需要配置文件。如果您的应用程序一切正常,它将打印以下消息:
Your Message : Hello World!
当@Beans具有彼此依赖关系时,表示依赖关系就像让一个bean方法调用另一个一样简单,如下所示:
package com.tutorialspoint;
import org.springframework.context.annotation.*;
@Configuration
public class AppConfig {
@Bean
public Foo foo() {
return new Foo(bar());
}
@Bean
public Bar bar() {
return new Bar();
}
}
在这里,foo bean通过构造函数注入接收对bar的引用。现在让我们看另一个工作示例。
让我们拥有一个运行良好的Eclipse IDE,并采取以下步骤来创建一个Spring应用程序:
Steps | Description |
---|---|
1 | Create a project with a name SpringExample and create a package com.tutorialspoint under the src folder in the created project. |
2 | Add required Spring libraries using Add External JARs option as explained in the Spring Hello World Example chapter. |
3 | Because you are using Java-based annotations, so you also need to add CGLIB.jar from your Java installation directory and ASM.jar library which can be downloaded from asm.ow2.org. |
4 | Create Java classes TextEditorConfig, TextEditor, SpellChecker and MainApp under the com.tutorialspoint package. |
5 | The final step is to create the content of all the Java files and Bean Configuration file and run the application as explained below. |
这是TextEditorConfig.java文件的内容
package com.tutorialspoint;
import org.springframework.context.annotation.*;
@Configuration
public class TextEditorConfig {
@Bean
public TextEditor textEditor(){
return new TextEditor( spellChecker() );
}
@Bean
public SpellChecker spellChecker(){
return new SpellChecker( );
}
}
这是TextEditor.java文件的内容
package com.tutorialspoint;
public class TextEditor {
private SpellChecker spellChecker;
public TextEditor(SpellChecker spellChecker){
System.out.println("Inside TextEditor constructor." );
this.spellChecker = spellChecker;
}
public void spellCheck(){
spellChecker.checkSpelling();
}
}
以下是另一个依赖类文件SpellChecker.java的内容
package com.tutorialspoint;
public class SpellChecker {
public SpellChecker(){
System.out.println("Inside SpellChecker constructor." );
}
public void checkSpelling(){
System.out.println("Inside checkSpelling." );
}
}
以下是MainApp.java文件的内容
package com.tutorialspoint;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.*;
public class MainApp {
public static void main(String[] args) {
ApplicationContext ctx =
new AnnotationConfigApplicationContext(TextEditorConfig.class);
TextEditor te = ctx.getBean(TextEditor.class);
te.spellCheck();
}
}
创建完所有源文件并添加所需的其他库后,让我们运行该应用程序。您应该注意,不需要配置文件。如果您的应用程序一切正常,它将打印以下消息:
Inside SpellChecker constructor.
Inside TextEditor constructor.
Inside checkSpelling.
该@Import注释允许从另一个配置类加载@Bean定义。考虑如下的ConfigA类-
@Configuration
public class ConfigA {
@Bean
public A a() {
return new A();
}
}
您可以在另一个Bean声明中的Bean声明上方导入,如下所示-
@Configuration
@Import(ConfigA.class)
public class ConfigB {
@Bean
public B b() {
return new B();
}
}
现在,无需在实例化上下文时同时指定ConfigA.class和ConfigB.class,只需按以下方式提供ConfigB-
public static void main(String[] args) {
ApplicationContext ctx = new AnnotationConfigApplicationContext(ConfigB.class);
// now both beans A and B will be available...
A a = ctx.getBean(A.class);
B b = ctx.getBean(B.class);
}
@Bean注释支持指定任意的初始化和销毁回调方法,就像Spring XML在bean元素上的init-method和destroy-method属性一样-
public class Foo {
public void init() {
// initialization logic
}
public void cleanup() {
// destruction logic
}
}
@Configuration
public class AppConfig {
@Bean(initMethod = "init", destroyMethod = "cleanup" )
public Foo foo() {
return new Foo();
}
}
默认范围是单例,但是您可以使用@Scope注释覆盖此范围,如下所示:
@Configuration
public class AppConfig {
@Bean
@Scope("prototype")
public Foo foo() {
return new Foo();
}
}