Servlet |VERIFIED|

A servlet is a Java programming language class that is used to extendthe capabilities of servers that host applications accessed by means of a request-responseprogramming model. Although servlets can respond to any type of request, they arecommonly used to extend the applications hosted by web servers. For such applications,Java Servlet technology defines HTTP-specific servlet classes.

The javax.servlet and javax.servlet.http packages provide interfaces and classes for writing servlets. Allservlets must implement the Servlet interface, which defines life-cycle methods. When implementing a genericservice, you can use or extend the GenericServlet class provided with theJava Servlet API. The HttpServlet class provides methods, such as doGet anddoPost, for handling HTTP-specific services.

Servlet

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A servlet is a small Java program that runs within a Web server. Servlets receive and respond to requests from Web clients, usually across HTTP, the HyperText Transfer Protocol. To implement this interface, you can write a generic servlet that extends javax.servlet.GenericServlet or an HTTP servlet that extends javax.servlet.http.HttpServlet. This interface defines methods to initialize a servlet, to service requests, and to remove a servlet from the server. These are known as life-cycle methods and are called in the following sequence: The servlet is constructed, then initialized with the init method. Any calls from clients to the service method are handled. The servlet is taken out of service, then destroyed with the destroy method, then garbage collected and finalized. In addition to the life-cycle methods, this interface provides the getServletConfig method, which the servlet can use to get any startup information, and the getServletInfo method, which allows the servlet to return basic information about itself, such as author, version, and copyright.Author:VariousSee Also:GenericServlet, HttpServletMethod SummaryAll Methods Instance Methods Abstract Methods Modifier and TypeMethod and Descriptionvoiddestroy()Called by the servlet container to indicate to a servlet that the servlet is being taken out of service.ServletConfiggetServletConfig()Returns a ServletConfig object, which contains initialization and startup parameters for this servlet.StringgetServletInfo()Returns information about the servlet, such as author, version, and copyright.voidinit(ServletConfig config)Called by the servlet container to indicate to a servlet that the servlet is being placed into service.voidservice(ServletRequest req, ServletResponse res)Called by the servlet container to allow the servlet to respond to a request.Method Detailinitvoid init(ServletConfig config) throws ServletExceptionCalled by the servlet container to indicate to a servlet that the servlet is being placed into service. The servlet container calls the init method exactly once after instantiating the servlet. The init method must complete successfully before the servlet can receive any requests. The servlet container cannot place the servlet into service if the init method Throws a ServletException Does not return within a time period defined by the Web server Parameters:config - a ServletConfig object containing the servlet's configuration and initialization parametersThrows:ServletException - if an exception has occurred that interferes with the servlet's normal operationSee Also:UnavailableException, getServletConfig()getServletConfigServletConfig getServletConfig()Returns a ServletConfig object, which contains initialization and startup parameters for this servlet. The ServletConfig object returned is the one passed to the init method. Implementations of this interface are responsible for storing the ServletConfig object so that this method can return it. The GenericServlet class, which implements this interface, already does this.Returns:the ServletConfig object that initializes this servletSee Also:init(javax.servlet.ServletConfig)servicevoid service(ServletRequest req, ServletResponse res) throws ServletException, IOExceptionCalled by the servlet container to allow the servlet to respond to a request. This method is only called after the servlet's init() method has completed successfully. The status code of the response always should be set for a servlet that throws or sends an error. Servlets typically run inside multithreaded servlet containers that can handle multiple requests concurrently. Developers must be aware to synchronize access to any shared resources such as files, network connections, and as well as the servlet's class and instance variables. More information on multithreaded programming in Java is available in the Java tutorial on multi-threaded programming.Parameters:req - the ServletRequest object that contains the client's requestres - the ServletResponse object that contains the servlet's responseThrows:ServletException - if an exception occurs that interferes with the servlet's normal operationIOException - if an input or output exception occursgetServletInfoString getServletInfo()Returns information about the servlet, such as author, version, and copyright. The string that this method returns should be plain text and not markup of any kind (such as HTML, XML, etc.).Returns:a String containing servlet informationdestroyvoid destroy()Called by the servlet container to indicate to a servlet that the servlet is being taken out of service. This method is only called once all threads within the servlet's service method have exited or after a timeout period has passed. After the servlet container calls this method, it will not call the service method again on this servlet. This method gives the servlet an opportunity to clean up any resources that are being held (for example, memory, file handles, threads) and make sure that any persistent state is synchronized with the servlet's current state in memory.Skip navigation linksOverviewPackageClassUseTreeDeprecatedIndexHelpPrev ClassNext ClassFramesNo FramesAll ClassesSummary: Nested | Field | Constr | MethodDetail: Field | Constr | MethodCopyright 1996-2015, Oracle and/or its affiliates. All Rights Reserved. Use is subject to license terms.

I started a new dynamic web project in Eclipse, I made an index.jsp page that just gets the user's name and sends it to the servlet, and is then supposed to print out Hello, [username]. The code is all sample code that the prof gave us and works for other people in my class.

To finish, you can use the method attribute in your form to choose the HTTP method that your browser will use to request the Servlet. If you don't provide, the default method is get. As I already said, if the get method is used, you need to implement the doGet method in the servlet.

I have a lot of experience in servlets and tomcat, but today was the second time I encountered something strange: after playing around with the servlet doGet logic, when I accessed the servlet it started download the file (instead of execute the logic!).It happens in all browsers, and it happens also when I deploy the webapp on different configuration of the tomcat (but still, on eclipse. maybe the bug is in the tomcat eclipse plugin?)

What is downloaded? The servlet source code? You have to compile the code to a .class file and put it in WEB-INF/classes. Eclipse should do that automatically if you put your java file in a Java Source folder.

Btw if you return online text and that's exactly what your servlet does with the content type text/plain, you should rather use for example jquery ajax to parse the text result and render it into the html or jsp from which the request is issued.

A Jakarta Servlet, formerly Java Servlet is a Java software component that extends the capabilities of a server. Although servlets can respond to many types of requests, they most commonly implement web containers for hosting web applications on web servers and thus qualify as a server-side servlet web API. Such web servlets are the Java counterpart to other dynamic web content technologies such as PHP and ASP.NET.

A Servlet is an object that receives a request and generates a response based on that request. The basic Servlet package defines Java objects to represent servlet requests and responses, as well as objects to reflect the servlet's configuration parameters and execution environment.

The package javax.servlet.http defines HTTP-specific subclasses of the GenericServlet. This package includes session management objects that track multiple requests and responses between the web server and a client.

Servlets can maintain state in session variables across many server transactions by using HTTP cookies, or URL mapping. The application can keep track of session and cookies by using sessions and cookies.[6] There are several ways for creating and URL mapping for a servlet. Before servlet 3.0 specification (Tomcat 7.0), configuring the web.xml to map a servlet to a URL was the only option. For applications using the servlet 3.0 specification or later, the @WebServlet annotation can be used to map any servlet to one or more URL patterns.

A web container is required for deploying and running a servlet. A web container (also known as a servlet container) is essentially the component of a web server that interacts with the servlets.[1] The web container is responsible for managing the lifecycle of servlets, mapping a URL to a particular servlet and ensuring that the URL requester has the correct access rights.

Servlets can be generated automatically from Jakarta Server Pages (JSP) by the Jakarta Server Pages compiler. The difference between servlets and JSP is that servlets typically embed HTML inside Java code, while JSPs embed Java code in HTML. In general, when using JSPs, embedding Java code in JSP is considered bad practice.[8] Instead, a better approach would be to move the back-end logic from the JSP to the Java code in the Servlet.[8] This ensures that the Servlet is only responsible for processing, and the JSP is only responsible for presenting the HTML,[8] allowing for a clear separation of concerns and conformance to the single-responsibility principle. be457b7860