Servlet chaining is a technique in which two or more servlets can cooperate in servicing a single request. In servlet chaining, one servlet’s output is piped to the next servlet’s input. This process continues until the last servlet is reached. Its output is then sent back to the client.

Servlet chaining refers to the process of invoking multiple servlets in a specific order to perform a sequence of related tasks in a Java web application. This is achieved by linking multiple servlets together, where the output of one servlet becomes the input for the next servlet in the chain. Servlet chaining is typically used to modularize and organize the processing logic in a web application.

The sequence of servlets is defined in the deployment descriptor (web.xml) or through annotations in modern servlet specifications (such as Servlet 3.0 onwards). Each servlet in the chain processes the request and may modify the request or response before passing it to the next servlet.

Servlet chaining can be useful in scenarios where different servlets handle specific aspects of a task, promoting code reuse, maintainability, and separation of concerns.

Here’s a simplified example using web.xml:

xml

<web-app>

<servlet>

<servlet-name>FirstServlet</servlet-name>

<servlet-class>com.example.FirstServlet</servlet-class>

</servlet>

<servlet>
<servlet-name>SecondServlet</servlet-name>
<servlet-class>com.example.SecondServlet</servlet-class>
</servlet>

<servlet-mapping>
<servlet-name>FirstServlet</servlet-name>
<url-pattern>/first</url-pattern>
</servlet-mapping>

<servlet-mapping>
<servlet-name>SecondServlet</servlet-name>
<url-pattern>/second</url-pattern>
</servlet-mapping>
</web-app>

In this example, when a request is made to the “/first” URL, it triggers the execution of FirstServlet, and its output may be used as input for SecondServlet mapped to “/second”. The order of execution is determined by the order of servlet mappings in the web.xml file.