ApplicationContext种类

今天药忘吃喽~ 2024-02-29 04:52 53阅读 0赞

### 5. Types of ApplicationContext ###

Spring provides different types of ApplicationContext containers [suitable][] for `different requirements`. These are implementations of the `ApplicationContext interface`. So let’s take a look at some of the common types of ApplicationContext.

#### 5.1. AnnotationConfigApplicationContext ####

[AnnotationConfigApplicationContext][] class was introduced in Spring 3.0.  
It can take classes annotated with @Configuration, @Component, and JSR-330 metadata as input.

ApplicationContext context = new AnnotationConfigApplicationContext(AccountConfig.class);
    AccountService accountService = context.getBean(AccountService.class);

#### 5.2. AnnotationConfigWebApplicationContext ####

[AnnotationConfigWebApplicationContext][] is a web-based variant of AnnotationConfigApplicationContext.

We may use this class when we configure Spring’s `ContextLoaderListener` servlet listener or a Spring MVC `DispatcherServlet` in a web.xml file.

Moreover, from Spring 3.0 onward, we can also configure this application context container programmatically. All we need to do is implement the [WebApplicationInitializer][] interface:

public class MyWebApplicationInitializer implements WebApplicationInitializer {
        
    
      public void onStartup(ServletContext container) throws ServletException {
        
        AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
        context.register(AccountConfig.class);
        context.setServletContext(container);
    
        // servlet configuration
      }
    }

--------------------

#### 5.3. XmlWebApplicationContext ####

If we use the XML based configuration in a web application, we can use the [XmlWebApplicationContext][] class.

As a matter of fact, configuring this container is like the AnnotationConfigWebApplicationContext class only, which means we can configure it in web.xml, or implement the WebApplicationInitializer interface:

public class MyXmlWebApplicationInitializer implements WebApplicationInitializer {
        
    
      public void onStartup(ServletContext container) throws ServletException {
        
        XmlWebApplicationContext context = new XmlWebApplicationContext();
        context.setConfigLocation("/WEB-INF/spring/applicationContext.xml");
        context.setServletContext(container);
    
        // Servlet configuration
      }
    }

--------------------

#### 5.4. FileSystemXMLApplicationContext ####

We use the [FileSystemXMLApplicationContext][] class to load an XML-based Spring configuration file from the file system or from URLs. This class is useful when we need to load the ApplicationContext programmatically. In general, test harnesses and standalone applications are some of the possible use cases for this.

For example, let’s see how we can create this Spring container and load the beans for our XML-based configuration:

String path = "C:/myProject/src/main/resources/applicationcontext/account-bean-config.xml";
    
    ApplicationContext context = new FileSystemXmlApplicationContext(path);
    AccountService accountService = context.getBean("accountService", AccountService.class);

--------------------

#### 5.5. ClassPathXmlApplicationContext ####

In case we want to load an XML configuration file from the classpath, we can use the [ClassPathXmlApplicationContext][] class. Similar to FileSystemXMLApplicationContext, it’s useful for test harnesses, as well as application contexts embedded within JARs.

So let’s see an example of using this class:

ApplicationContext context = new ClassPathXmlApplicationContext("applicationcontext/account-bean-config.xml");
    AccountService accountService = context.getBean("accountService", AccountService.class);

参考：  
[The Spring ApplicationContext][]

[suitable]: https://dict.youdao.com/w/suitable%20/#keyfrom=dict2.top
[AnnotationConfigApplicationContext]: https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/context/annotation/AnnotationConfigApplicationContext.html
[AnnotationConfigWebApplicationContext]: https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/web/context/support/AnnotationConfigWebApplicationContext.html
[WebApplicationInitializer]: https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/web/WebApplicationInitializer.html
[XmlWebApplicationContext]: https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/web/context/support/XmlWebApplicationContext.html
[FileSystemXMLApplicationContext]: https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/context/support/FileSystemXmlApplicationContext.html
[ClassPathXmlApplicationContext]: https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/context/support/ClassPathXmlApplicationContext.html
[The Spring ApplicationContext]: https://www.baeldung.com/spring-application-context