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This article is to share with you about how to analyze the Web application of Servlet. The editor thinks it is very practical, so I share it with you. I hope you can get something after reading this article.

A powerful feature of Java Servlet API is its ability to work with form data relatively easily. Instead of looking around for environment variables in traditional CGI development, you can use Servlets to access form and query string data by routinely calling Java methods. Let's take a look at how it works. You can download the code for the example of this article here.

Load Servlet

When Servlet is loaded, the Servlet engine calls the init method of Servlet. This method is called only once when the Servlet is loaded and passes the configuration data as an instance of the ServletConfig class. The ServletConfig object contains information about the Servlet engine and the Servlet runtime environment.

The ServletConfig object exposes initialization data to the Web application that Servlet operates on. Using the getInitParamete (StringparamName) method, you can access this data, as shown in Listing A.

Before the destruction

The Servlet class exposes a method, destroy, which is called by the Servlet engine when Servlet is normally unloaded. This method is called when all threads of the Servlet have been unloaded or after the specified time has elapsed. It is used to save Servlet or clear resources, see Listing B.

Servlet must be able to handle multiple requests from multiple customers. Since any number of customers will access a Servlet at the same time, any method other than init must be implemented in a thread-safe manner. The following figure shows the relationship between multiple user requests and a single Servlet instance.

Multiple customer requests for a single servlet

How does cookie work

Because it is a single Servlet that handles requests from multiple users, Servlet needs a mechanism to determine which customer initiated which request. The most common mechanism used to identify a customer's request is the use of HTTP cookie. HTTP cookie is any length of information that is passed between the browser client and the server using the HTTP header.

When Servlet receives a request from a customer with cookie, Servlet uses the information in cookie to determine which customer and responds intelligently to the customer. This may seem like an insignificant feature, but it brings the interaction between customers and Servlet-based Web applications into a new space. In particular, this feature enables Web applications to save and restore customer state between requests.

Servlet's ability to maintain customer status allows customers to talk to Servlet-based Web applications, rather than limiting them to one-time request / response transactions. Java Servlet API provides a class called Cookie, which can be retrieved from a request or saved in a response. This class also allows you to get information or setting information from cookie. For example, a program segment in Listing C retrieves the cookie from the request, prints the information for each cookie, or creates a new cookie and adds it to the response.

ECourt session

With the ability to maintain customer state between requests and responses, Servlet-oriented Web application developers can effectively design Web applications that can interact with customers for a period of time called a session. The session can be used by Servlet developers to receive data from the customer and pass the data to the customer based on the information received in the previous request and / or response. This helps to develop efficient Web applications such as shopping carts, online banking, and Web mail.

Java Servlet API provides a class called HttpSession where developers can save and retrieve arbitrary objects that contain information about customer conversations. The object is saved as a name / value in the HttpSession class and is retrieved from it. Listing D is an example of this.

The above is how to analyze the Web application of Servlet. The editor believes that there are some knowledge points that we may see or use in our daily work. I hope you can learn more from this article. For more details, please follow the industry information channel.

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