基于Java配置选项,可以编写大多数的Spring不用配置XML,但有几个基于Java的注释的帮助下解释。
@Configuration & @Bean 注解:
注释类与@Configuration表示这个类可以使用Spring IoC容器为bean定义的来源。在@Bean 注解告诉Spring的注解为@Bean的一个方法将返回应注册为在Spring应用程序上下文中的bean对象。最简单可行的@Configuration类将如下所示:
package com.yiibai;import org.springframework.context.annotation.*;@ConfigurationpublicclassHelloWorldConfig{@BeanpublicHelloWorld helloWorld(){returnnewHelloWorld();}}
上面的代码将等同于下面的XML配置:
<beans><beanid="helloWorld"class="com.yiibai.HelloWorld"/></beans>
下面注解为@Bean的方法名称作为工作bean的id,它创建并返回实际的bean。配置类可以有声明多个@Bean。一旦配置类定义,可以加载和提供他们使用AnnotationConfigApplicationContext 如下,以Spring容器:
publicstaticvoid main(String[] args){ApplicationContext ctx =newAnnotationConfigApplicationContext(HelloWorldConfig.class);HelloWorld helloWorld = ctx.getBean(HelloWorld.class); helloWorld.setMessage("Hello World!"); helloWorld.getMessage();}
可以加载各种配置类别如下:
publicstaticvoid main(String[] args){AnnotationConfigApplicationContext ctx =newAnnotationConfigApplicationContext(); ctx.register(AppConfig.class,OtherConfig.class); ctx.register(AdditionalConfig.class); ctx.refresh();MyService myService = ctx.getBean(MyService.class); myService.doStuff();}例子:
让我们使用Eclipse IDE,然后按照下面的步骤来创建一个Spring应用程序:
1 | Create a project with a name SpringExample and create a package com.yiibai 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.yiibaipackage. |
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. |
这里是HelloWorldConfig.java文件的内容:
package com.yiibai;import org.springframework.context.annotation.*;@ConfigurationpublicclassHelloWorldConfig{@BeanpublicHelloWorld helloWorld(){returnnewHelloWorld();}}
这里是HelloWorld.java的文件的内容:
package com.yiibai;publicclassHelloWorld{privateString message;publicvoid setMessage(String message){this.message = message;}publicvoid getMessage(){System.out.println("Your Message : "+ message);}}
以下是MainApp.java文件的内容:
package com.yiibai;import org.springframework.context.ApplicationContext;import org.springframework.context.annotation.*;publicclassMainApp{publicstaticvoid main(String[] args){ApplicationContext ctx =newAnnotationConfigApplicationContext(HelloWorldConfig.class);HelloWorld helloWorld = ctx.getBean(HelloWorld.class); helloWorld.setMessage("Hello World!"); helloWorld.getMessage();}}
创建所有的源文件并添加所需的额外(外部)的库,让我们运行应用程序。应该注意,不需要配置文件。如果一切顺利,这将打印以下信息:
Your Message : Hello World!注入Bean的依赖关系:
当@Bean对彼此的依赖,表达这种依赖很简单,只要有一个Bean的方法调用另一个如下:
package com.yiibai;import org.springframework.context.annotation.*;@ConfigurationpublicclassAppConfig{@BeanpublicFoo foo(){returnnewFoo(bar());}@BeanpublicBar bar(){returnnewBar();}}
在这里,Bean接收基准通过构造函数注入。现在,让我们看到一个正常工作的例子:
例子:让我们使用Eclipse IDE,然后按照下面的步骤来创建一个Spring应用程序:
1 | Create a project with a name SpringExample and create a package com.yiibai 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 thecom.yiibai 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. |
这里是TextEditorConfig.java文件的内容:
package com.yiibai;import org.springframework.context.annotation.*;@ConfigurationpublicclassTextEditorConfig{@BeanpublicTextEditor textEditor(){returnnewTextEditor( spellChecker());}@BeanpublicSpellChecker spellChecker(){returnnewSpellChecker();}}
这里是TextEditor.java文件的内容:
package com.yiibai;publicclassTextEditor{privateSpellChecker spellChecker;publicTextEditor(SpellChecker spellChecker){System.out.println("Inside TextEditor constructor.");this.spellChecker = spellChecker;}publicvoid spellCheck(){ spellChecker.checkSpelling();}}
下面是另外一个相关的类文件SpellChecker.java内容:
package com.yiibai;publicclassSpellChecker{publicSpellChecker(){System.out.println("Inside SpellChecker constructor.");}publicvoid checkSpelling(){System.out.println("Inside checkSpelling.");}}
以下是MainApp.java文件的内容:
package com.yiibai;import org.springframework.context.ApplicationContext;import org.springframework.context.annotation.*;publicclassMainApp{publicstaticvoid main(String[] args){ApplicationContext ctx =newAnnotationConfigApplicationContext(TextEditorConfig.class);TextEditor te = ctx.getBean(TextEditor.class); te.spellCheck();}}
创建所有的源文件并添加所需的额外的库完成,让我们运行应用程序。应该注意,不需要配置文件。如果一切顺利,这将打印以下信息:
Inside SpellChecker constructor. Inside TextEditor constructor. Inside checkSpelling.@Import 注解:
@ import的注解允许加载@Bean从另一个配置类定义。考虑一个配置类,如下所示:
@ConfigurationpublicclassConfigA{@Beanpublic A a(){returnnew A();}}
您可以在另一个bean声明导入上述bean声明如下:
@Configuration@Import(ConfigA.class)publicclassConfigB{@Beanpublic B a(){returnnew A();}}
现在,不需要实例化的前提下,当同时指定配置A.class和配置B.class,只有Config B类需要如下提供:
publicstaticvoid main(String[] args){ApplicationContext ctx =newAnnotationConfigApplicationContext(ConfigB.class);// now both beans A and B will be available... A a = ctx.getBean(A.class); B b = ctx.getBean(B.class);}生命周期回调:
@Bean注解支持指定任意的初始化和销毁回调方法,就像Spring的XML的初始化方法和bean元素销毁方法的属性:
publicclassFoo{publicvoid init(){// initialization logic}publicvoid cleanup(){// destruction logic}}@ConfigurationpublicclassAppConfig{@Bean(initMethod ="init", destroyMethod ="cleanup")publicFoo foo(){returnnewFoo();}}指定Bean的适用范围:
默认范围是单例,但可以使用@Scope注解来覆盖此如下:
@ConfigurationpublicclassAppConfig{@Bean@Scope("prototype")publicFoo foo(){returnnewFoo();}}
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