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Editor to share with you how to call Servlet, I believe that most people do not know much about it, so share this article for your reference, I hope you can learn a lot after reading this article, let's go to know it!

To call a Servlet or Web application, use any of the following methods: call Servlet by URL, call Servlet in the < FORM > tag, call Servlet in the < SERVLET > tag, call Servlet in the JSP file, and call Servlet in the ASP file.

1. Servlet is called by URL

There are two ways to call the Servlet from the browser using Servlet's URL:

(1) specify Servlet name: when using WebSphere Application Server Manager to add (register) an Servlet instance to the server configuration, you must specify the value of the "Servlet name" parameter. For example, you can specify hi as the Servlet name of the HelloWorldServlet. To invoke the Servlet, open http://your.server.name/servlet/hi. You can also specify that Servlet and the class use the same name (HelloWorldServlet). In this case, the instance of Servlet will be called by http://your.server.name/servlet/HelloWorldServlet.

(2) specify the Servlet alias: use the WebSphere Application Server Manager to configure the Servlet alias, which is the shortcut URL used to invoke Servlet. The Servlet name is not included in the shortcut URL.

two。 Specify the calling Servlet in the < FORM > tag

You can call Servlet in the < FORM > tag. The HTML format enables users to enter data on a Web page (that is, from a browser) and submit it to Servlet. For example:

< FORMMETHOD= "GET" ACTION= "/ servlet/myservlet" > < OL > < INPUTTYPE= "radio" NAME= "broadcast" VALUE= "am" > AM < BR > < INPUTTYPE= "radio" NAME= "broadcast" VALUE= "fm" > FM < BR > > (tags, buttons, and other prompts for text input areas. ) < / FORM >

The ACTION feature indicates the URL used to invoke Servlet. With regard to the features of METHOD, if the information entered by the user is submitted to the Servlet through the GET method, the Servlet must give priority to the doGet () method. Conversely, if the information entered by the user is submitted to the Servlet through the POST method, the Servlet must give priority to the doPost () method. When using the GET method, the information provided by the user is the URL encoding represented by the query string. There is no need to encode the URL because it is done by the form. The URL-encoded query string is then appended to the ServletURL, and the entire URL submission is completed. The URL-encoded query string matches the value selected by the user with the name of the visual part based on the interaction between the user and the visual part. For example, consider that the previous HTML code snippet will be used to display buttons (labeled AM and FM), and if the user selects the FM button, the query string will have a pairing operation containing name=value as broadcast=fm. Because in this case, Servlet will respond to HTTP requests, Servlet should be based on the HttpServlet class. Servlet should use the GET or POST method based on the user information in the query string submitted to it, and use the doGet () or doPost () method accordingly.

3. Specify the calling Servlet in the < SERVLET > tag

When you use the < SERVLET > tag to invoke Servlet, you don't need to create a complete HTML page as you do with the < FORM > tag. Instead, the output of Servlet is only part of the HTML page and is dynamically embedded in other static text in the original HTML page. All of this happens on the server, and only the resulting HTML page is sent to the user. It is recommended that you use the < SERVLET > tag in the Java server page (JSP) file. See about JSP technology

The original HTML page contains < SERVLET > and < / SERVLET > tags. Servlet will be called in these two tags, and the response of the Servlet will cover everything between the two tags and the tag itself. If the user's browser can see the HTML source file, the user will not see the < SERVLET > and < / SERVLET > tags. To use this method on DominoGoWebserver, enable the server-side include feature on the server. Part of the enabling process will involve adding a special file type SHTML. When the Web server receives a request for a Web page with the extension SHTML, it searches for the < SERVLET > and < / SERVLET > tags. For all supported Web servers, the WebSphere application server processes all information between SERVLET tags. The following HTML code snippet shows how to use this technique.

< SERVLET NAME= myservlet "CODE=" myservlet.class "CODEBASE=" url "initparm1=" value "> < PARAM NAME=" parm1 "VALUE=" value "> < / SERVLET >

The use of the NAME and CODE properties provides flexibility in use. You can use only one of the attributes, or you can use both. The NAME attribute specifies the name of the Servlet (configured using the WebSphere application server manager) or the name of the Servlet class without the .class extension. The CODE property specifies the Servlet class name. When using the WebSphere application server, it is recommended that you specify NAME and CODE, or only NAME when NAME specifies the Servlet name. If only CODE is specified, a Servlet instance of NAME=CODE is created. The loaded Servlet assumes that the Servlet name matches the name specified in the NAME property. Other SHTML files can then successfully use the NAME attribute to specify the name of the Servlet and call the loaded Servlet. The value of NAME can be used directly in the URL where you want to call Servlet. If both NAME and CODE exist, and NAME specifies an existing Servlet, the Servlet specified in NAME is usually used. Because Servlet creates part of the HTML file, when creating a Servlet, you will probably use a subclass of HttpServlet and give priority to the doGet () method (because the GET method is the default method to provide information to Servlet). Another option is to give priority to the service () method. In addition, CODEBASE is optional, which specifies the URL of the remote system on which the Servlet is mounted. Use the WebSphere Application Server Manager to configure the remote Servlet mount system from the JAR file.

In the tag example above, initparm1 is the initialization parameter name and value is the value of that parameter. You can specify a collection of multiple name-value pairs. Use the getInitParameterNames () and getInitParameter () methods of the ServletConfig object (passed to the init () method of Servlet) to find a string array of parameter names and values. In the example, parm1 is the parameter name and a value is not set until Servlet is initialized. Because parameters set with the < PARAM > tag can only be used by using the method of the request object, the server must call the Servletservice () method to pass the request from the user. To get request information about the user, use the getParameterNames (), getParameter (), and getParameterValues () methods.

Initialization parameters are persistent. Suppose a client invokes Servlet by calling a SHTML file that contains some initialization parameters. It is also assumed that the second client invokes the same Servlet by calling the second SHTML file to invoke Servlet, and no initialization parameters are specified in that SHTML. Then the initialization parameter set during the * call to Servlet will always be available, and all subsequent Servlet called through all other SHTML files will not change this parameter. The initialization parameters cannot be reset until Servlet calls the destroy () method. For example, if another SHTML file specifies a different initialization parameter value, although Servlet is loaded at this time, the value will still be ignored.

4. Call Servlet in the JSP file

You can call Servlet from a JavaServer page (JSP) file. Please refer to the JSP technology section.

5. Call Servlet in the ASP file

If there is a legacy ASP file on Microsoft Internet Information Server (IIS) and the ASP file cannot be migrated to a JSP file, you can use the ASP file to call Servlet. ASP support in the WebSphere application server includes an ActiveX control for embedding Servlet. The methods and properties of ActiveX controlling AspToServlet are described below.

The method is described as follows:

(1) String ExecServletToString (String servletName); executes ServletName and returns its output to a string.

(2) ExecServlet (String servletName); execute ServletName and send its output directly to the HTML page.

(3) String VarValue (String varName); get a preset variable value (other formats).

(4) VarValue (String varName, String newVal); sets the variable value. The total size occupied by variables should be less than 0.5 kilobytes (Kbyte). And use these variables only for configuration files.

Its properties are as follows:

◆ Boolean WriteHeaders; if the attribute is true, the title provided by Servlet is written to the user. The default value is false.

◆ Boolean OnTest; if this property is true, the server logs the message to the generated HTML page. The default value is false.

The following example of an ASP call Servlet script is written in Microsoft Visual Basic Scripting (VBScript).

<% 'Small sample asp file to show the capabilities of the servlets and the ASP GateWay...% > < H1 > Starting the ASP- > Java Servlet demo < / H1 > <%' Create a Servlet gateway object and initialize it... Set javaasp = Server.CreateObject ("AspToServlet.AspToServlet") 'Setting these properties is only for the sake of demo. ' These are the default values... Javaasp.OnTest = False javaasp.WriteHeaders = False 'Add several variables... Javaasp.VarValue ("gal") = "lag" javaasp.VarValue ("pico") = "ocip" javaasp.VarValue ("tal") = "lat" javaasp.VarValue ("paz") = "zap" javaasp.VarValue ("variable name with spaces") = "variable value with spaces"% > < BR > Lets check the variables <% Response.Write ("variable gal =") Response.Write (javaasp.VarValue ("gal"))% > < BR > <% Response.Write ("variable picopico =" & javaasp.VarValue ("pico"))% > < BR > < HR > <% galout = javaasp.ExecServletToString ("SnoopServlet") If javaasp.WriteHeaders = True Then% > Headers were written <% Else% > Headers were not written <% End If Response.Write (galout)% > < H1 > The End... < / H1 > these are all the contents of the article "how to call Servlet" Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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