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POwhy statement xmlhttp.onreadystatechange cause this program work once only?
 

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  1. POwhy statement xmlhttp.onreadystatechange cause this program work once only?
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    <p>i make a simple REST web service consumer using HTML and javascript. here's the code:</p> <pre><code>&lt;!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"&gt; &lt;html&gt; &lt;head&gt; &lt;title&gt;&lt;/title&gt; &lt;meta http-equiv="Content-Type" content="text/html; charset=UTF-8"&gt; &lt;script language="javascript"&gt; var xmlhttp; function getdetails() { var empno = document.getElementById("empno"); var url = "http://localhost:8080/TestWS1/rest/hello/" + empno.value; xmlhttp = new XMLHttpRequest(); //@slaks: i put it here xmlhttp.open('GET',url,true); xmlhttp.send(null); xmlhttp.onreadystatechange = function() { var empname = document.getElementById("empname"); var age = document.getElementById("age"); if (xmlhttp.readyState == 4) { //alert(xmlhttp.status); if ( xmlhttp.status == 200) { var det = eval( "(" + xmlhttp.responseText + ")"); if (det.age &gt; 0 ) { empname.value = det.name; age.value = det.age; } else { empname.value = ""; age.value =""; alert("Invalid Employee ID"); } } else alert("Error -&gt;" + xmlhttp.responseText); } } } &lt;/script&gt; &lt;/head&gt; &lt;body&gt; &lt;h1&gt;Call Employee Service &lt;/h1&gt; &lt;table&gt; &lt;tr&gt; &lt;td&gt;Enter Employee ID : &lt;/td&gt; &lt;td&gt;&lt;input type="text" id="empno" size="10"/&gt; &lt;input type="button" value="Get Details" onclick="getdetails()"/&gt; &lt;/tr&gt; &lt;tr&gt; &lt;td&gt;Enter Name : &lt;/td&gt; &lt;td&gt;&lt;input type="text" readonly="true" id="empname" size="20"/&gt; &lt;/td&gt; &lt;/tr&gt; &lt;tr&gt; &lt;td&gt;Employee Age : &lt;/td&gt; &lt;td&gt;&lt;input type="text" readonly="true" id="age" size="10"/&gt; &lt;/td&gt; &lt;/tr&gt; &lt;/table&gt; &lt;/body&gt; &lt;/html&gt; </code></pre> <p>that code only show an employee name and age from the REST web service on the HTML textbox when a getDetail button is pressed. the parameter is employee number (empNo).</p> <p>the main problem is, why this code only works once?? </p> <p>for example, if i put 1 on the empNo textbox and i pressed getDetail button, for the first time only, it will display the name and the age of the employee based on employee number that i was entered before. but for the second or third i press the getDetail button, it not works anymore. i've tried to give some alert to help me for debugging that code but the result is xmlhttp.onreadystatechange = function() only works once on the first time i pressed the getDetail button.</p> <p>has anyone know how to solve this problem?? really stuck in here.. thanks a lot for helping me..</p> <p>FYI: here's my web service code:</p> <pre><code>package com.webservices.TestWS1; import javax.ws.rs.GET; import javax.ws.rs.Path; import javax.ws.rs.PathParam; import javax.ws.rs.Produces; import javax.ws.rs.core.MediaType; //@Path("/hello") @Path("/hello/{empno}") public class Hello { @GET // this method process GET request from client @Produces("application/json") // sends JSON public String getJson( @PathParam("empno") int empno) { // empno represents the empno sent from client switch(empno) { case 1 : return "{'name':'George Koch', 'age':58}"; case 2: return "{'name':'Peter Norton', 'age':50}"; default: return "{'name':'unknown', 'age':-1}"; } // end of switch } // end of } </code></pre>
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