The technical principles and application example of the Common Annotations 1.2 API framework in the Java class library
The technical principles and application example of the Common Annotations 1.2 API framework in the Java class library
The Common Annotations 1.2 API framework in the Java class library is part of the Java EE 5 specification. It introduces a series of meta -solutions to simplify metadata annotations in the Java program.Metadata annotations refer to data used to describe classes, fields or methods, such as author, version number and other information.Common Annotions 1.2 API provides a standard way to manage and handle these annotations, thereby simplifying the work of developers.
Technical principle
Common Annotations 1.2 API framework mainly contains some commonly used meta -solutions, such as@generated,@postconstruct,@predestRoy, etc.These meta -annotations can be used to process metadata annotations of class, methods, or fields during runtime, so that developers can configure and manage the Java program more flexibly.
The technical principle of the framework is mainly through the Java's reflection mechanism to achieve the processing of metadata.When the program is running, you can obtain metadata annotations on the class, methods or fields through reflection, and perform corresponding logic according to the definition of the annotation.In this way, developers can configure the behavior of the program through metadata annotations to achieve more flexible and easy -to -maintain code.
Applications
Below we take a simple web application as an example to demonstrate the application instance of Common Annotations 1.2 API framework.In this example, we will use the @PostConStruct and @predestroy annotations in the Common Annotations 1.2 API to initialize and destroy a Servlet component.
First of all, we need to add @PostConStructs to the Servlet class of the web application and @Predestroy annotations, and add logical processing code to the corresponding method.The following is an example code:
import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class MyServlet extends HttpServlet {
@PostConstruct
public void init() {
// Initialize logic processing code
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// Servlet processing logic code
}
@PreDestroy
public void destroy() {
// Destroy logic processing code
}
}
In this example, we use @PostConStruct annotations to mark the init () method to perform corresponding logic when the service initialization.The @Predestroy annotation marked the Destroy () method, and executed the corresponding logic when the service was destroyed.
In addition, we also need to add the following configuration to the web.xml file to enable the support of the Common Annotations 1.2 API framework:
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
<metadata-complete>true</metadata-complete>
</web-app>
Through the above examples, we can see the application example of the Common Annotations 1.2 API framework, which can achieve the initialization and destruction logic of SERVLET through metadata annotations.This method makes the code more concise and easy to maintain, bringing a better development experience.
