The working principle and implementation of the Javax Interableptor API

Javax Interceptor API (interceptor API) is part of the Java EE platform, which provides a mechanism to intercept, pre -processing and post -processing application requests and responses.The interceptor API can be used to apply universal processing logic at the cross -cutting focus, such as security, transaction management, and log records. The working principle of the interceptor is based on the proxy mode.It inserts the interceptor code before and after the target method is executed, from the mobility to trigger the interceptor logic.The interceptor code can perform customized operations before and after the implementation of the target method.For example, parameter verification can be performed before the target method, and the running time of the method can be recorded after the target method is completed. Below is a simple example to explain the implementation of the interceptor API: First of all, we need to create a interceptor class to implement javax.interceptor.interceptor interface.This interface contains two methods: @Aroundinvoke and @PostConStruct.@AnDinvoke method is called before and after the target method execution, while the @PostConStruct method is called when the interceptor is initialized. import javax.interceptor.AroundInvoke; import javax.interceptor.Interceptor; import javax.interceptor.InvocationContext; @Interceptor public class LoggingInterceptor { @AroundInvoke public Object logMethodInvocation(InvocationContext context) throws Exception { System.out.println("Before method: " + context.getMethod().getName()); Object result = context.proceed (); // Call the target method System.out.println("After method execution"); return result; } } In our application code, we need to use the interceptor to intercept a specific method.We can specify the interceptor class on the target method using @InterCeptors annotations. import javax.ejb.Stateless; import javax.interceptor.Interceptors; @Stateless public class ExampleService { @Interceptors(LoggingInterceptor.class) public void doSomething() { System.out.println("Doing something..."); } } In the above example, when calling the Dosomething method in Exampleservice, LoggingInterceptor will be triggered.It will print "BEFORE METHOD: DOSOMETHING" before the method execution, and print "After Method Execution" after the method execution. To activate the interceptor, we need to configure it in deployment descriptive (such as web.xml or ejb-jar.xml).Here is a deployment descriptor example (EJB-JAR.XML), which contains the configuration of the interceptor: <ejb-jar xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/ejb-jar_3_2.xsd" version="3.2"> <interceptors> <interceptor> <interceptor-class>com.example.LoggingInterceptor</interceptor-class> </interceptor> </interceptors> <enterprise-beans> <session> <ejb-name>ExampleService</ejb-name> <interceptor-binding> <ejb-name>ExampleService</ejb-name> <interceptor-class>com.example.LoggingInterceptor</interceptor-class> </interceptor-binding> </session> </enterprise-beans> </ejb-jar> The Internet element in the configuration is used to specify the global interceptor, and the interceptor-binding element is used to bind the interceptor to a specific EJB component. By using the Javax Interceptor API, we can implement the interceptor to intercept and customize different application requests and responses.This mechanism can simplify repeatable code, improve reuse, and achieve consistency processing logic in the application.