如何在不离开页面的情况下从servlet返回字符串？

Question

以下是图片：

我有一个带有表单的html/jsp页面。

    <div id = "divAttributes">
        <form id = 'fid' method = "post" action = "RunQuery">
            Id Number: <input type= "text" name = "foo" id = "txtFoo"/><br/>        
            <input type = "checkbox" id = "chboxZap" value = "zap"/>Foo<br/>
            <input type = "checkbox" id = "chboxBar" value = "bar"/>Bar<br/>
            <input type= "submit" id = "btnSubmit" value = "submit" onclick = "setDisabled('divAttributes', true)"/><br/>
        </form>
    </div>

当用户按下提交按钮时，我想将表单中包含的信息发送到servlet，然后servlet将进行一些处理并返回字符串。

public void doPost(HttpServletRequest request,
                   HttpServletResponse response) throws IOException {

    response.setContentType("text/plain");

    ReturnCode rc = world.hello.MyMainClass.wait(request.getParameter("foo"));

    /*I want to return the RC, which is a bool, a string, and another object, which in this case is a string*/
}

然后将该字符串发送到另一个servlet，该servlet将保存一个文件。

我已经将servlet保存到文件中：

public void doPost(HttpServletRequest request,
                   HttpServletResponse response) throws IOException {
    response.setContentType("text/plain");
    response.setHeader("Content-Disposition",
            "attachment;filename=downloadname.txt");

    ServletContext ctx = getServletContext();

    String s = new String(request.getParameter("data"));

    InputStream is = new ByteArrayInputStream(s.getBytes());

    int read = 0;
    byte[] bytes = new byte[BYTES_DOWNLOAD];

    OutputStream os = response.getOutputStream();

    while ((read = is.read(bytes)) != -1) {
        os.write(bytes, 0, read);
    }
    os.flush();
    os.close();
}

我有两个问题：

>

如何将值从servlet返回到调用它的HTML页面，并从那里访问它们？

Answer 1

使用AJAX！

AJAX允许您创建一个AJAX Javascript对象，并向该对象返回HttpResponse。

eg.

function myAjaxRequest()
{
var xmlhttp; /*our ajax object*/

        if (window.XMLHttpRequest)
          {// code for IE7+, Firefox, Chrome, Opera, Safari
          xmlhttp=new XMLHttpRequest();
          }
        else
          {// code for IE6, IE5
          xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
          }
        setVisible('loading', true) ;

        /*this function called when ajax state changes*/
        xmlhttp.onreadystatechange=function()
          {
          /*when the query has completed successfully*/
          if (xmlhttp.readyState==4 && xmlhttp.status==200)
            {
                /*now you can do what you want with your response text!*/
                var mystring= xmlhttp.responseText;
                alert(mystring);
            }

          }

        /*the URL query we want to run*/
        var query = "RunQuery?foo="+$('#txtFoo').val();
        alert(query);

        /*AJAX object runs the query*/
        xmlhttp.open("GET", query, true); 
        xmlhttp.send();     
}       

Answer 2

JavaScript，更具体地说，Ajax将帮助您。如果在HTML中包含一个具有良好Ajax支持的库（比如jQuery），那么可以在保持页面不变的同时调用servlet。

因此，您可以调用一个JavaScript函数，对两个servlet使用嵌套的Ajax帖子，而不是通过按钮提交表单：

function submitForm() {
  $.post( 'url/to/firstServlet', { text: $('#txtFoo').val() }, function(dataFromFirst) {
    $.post( 'url/to/secondServlet', { data: dataFromFirst }, function(dataFromSecond) {
      // handle response from second servlet
    });
  });
}