calling a java servlet from javascript

Question

I am trying to create a web application using the MVC design pattern  For the GUI part I would like to use JavaScript  And for the controller Java Servlets   Now I have never really worked with JavaScript  so I m having a hard time figuring out how to call a Java Servlet from JavaScript and how to get the response from the Servlet    Can anybody help me out

User · Answer

function callServlet        document getElementById  adminForm   action    Administrator    document getElementById  adminForm   method    GET    document getElementById  adminForm   submit          lt button type  submit   onclick  callServlet    align  center  gt  Register lt  button gt

User · Answer

Sorry  I read jsp not javascript   You need to do something like  note that this is a relative url and may be different depending on the url of the document this javascript is in    document location    path to servlet     Where your servlet-mapping in web xml looks something like this    lt servlet-mapping gt       lt servlet-name gt someServlet lt  servlet-name gt       lt url-pattern gt  path to servlet  lt  url-pattern gt   lt  servlet-mapping gt

User · Answer

The code here will use AJAX to print text to an HTML5 document dynamically  Ajax code is similar to book Internet  amp  WWW  Deitel     Javascript code   var asyncRequest      function start        try               asyncRequest   new XMLHttpRequest            asyncRequest addEventListener  readystatechange   stateChange  false           asyncRequest open  GET     Test   true            Test is url to Servlet          asyncRequest send null             catch exception           alert  Request failed            function stateChange    if asyncRequest readyState    4  amp  amp  asyncRequest status    200            var text   document getElementById  text                text is an id of a      text innerHTML   asyncRequest responseText              div in HTML document          window addEventListener  load   start    false     Servlet java code   public class Test extends HttpServlet   Override public void doGet HttpServletRequest req  HttpServletResponse resp      throws IOException          resp setContentType  text plain            resp getWriter   println  Servlet wrote this   Test java               HTML document    lt div id    text  gt  lt  div gt    EDIT  I wrote answer above when I was new with web programming  I let it stand  but the javascript part should definitely be in jQuery instead  it is 10 times easier than raw javascript

User · Answer

So you want to fire Ajax calls to the servlet  For that you need the XMLHttpRequest object in JavaScript  Here s a Firefox compatible example    lt script gt      var xhr   new XMLHttpRequest        xhr onreadystatechange   function             if  xhr readyState    4                var data   xhr responseText              alert data                       xhr open  GET      pageContext request contextPath  myservlet   true       xhr send null    lt  script gt    This is however very verbose and not really crossbrowser compatible  For the best crossbrowser compatible way of firing ajaxical requests and traversing the HTML DOM tree  I recommend to grab jQuery  Here s a rewrite of the above in jQuery    lt script src  http   code jquery com jquery-latest min js  gt  lt  script gt   lt script gt        get    pageContext request contextPath  myservlet   function data            alert data            lt  script gt    Either way  the Servlet on the server should be mapped on an url-pattern of  myservlet  you can change this to your taste  and have at least doGet   implemented and write the data to the response as follows   String data    Hello World    response setContentType  text plain    response setCharacterEncoding  UTF-8    response getWriter   write data     This should show Hello World  in the JavaScript alert   You can of course also use doPost    but then you should use  POST  in xhr open   or use   post   instead of   get   in jQuery   Then  to show the data in the HTML page  you need to manipulate the HTML DOM  For example  you have a    lt div id  data  gt  lt  div gt    in the HTML where you d like to display the response data  then you can do so instead of alert data  of the 1st example   document getElementById  data   firstChild nodeValue   data    In the jQuery example you could do this in a more concise and nice way       data   text data     To go some steps further  you d like to have an easy accessible data format to transfer more complex data  Common formats are XML and JSON  For more elaborate examples on them  head to How to use Servlets and Ajax

User · Answer

I really recommend you use jquery for the javascript calls and some implementation of JSR311 like jersey for the service layer  which would delegate to your controllers    This will help you with all the underlying logic of handling the HTTP calls and your data serialization  which is a big help

User · Answer

var button   document getElementById   lt  lt button-id gt  gt     button addEventListener  click   function       window location href    lt  lt full-servlet-path gt  gt    eg  http   localhost 8086 xyz servlet

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