Take the jnlp file below for example(there is no space before codebase)
<?xml version="1.0" encoding="UTF-8"?>
<jnlp spec="1.0+"
codebase="http://127.0.0.1:8080/runtimeArgs/html/"
 href="RuntimeArgsUnTrustedPrintHeapAtGC.jnlp">
  <information>
    <title>RuntimeArgs Test Applet Demo</title>
    <vendor>Sun Microsystems, Inc.</vendor>
    <offline-allowed />
   <shortcut online="false">
      <desktop/>
      <menu submenu="Sun Microsystems Applets"/>
    </shortcut>
  </information>
  <resources>
      <j2se version="1.5+" java-vm-args="-XX:+PrintHeapAtGC"/>
        <jar href="../classes/test.jar"/>
        <jar href="../classes/helper.jar"/>
    </resources>
    <applet-desc main-class="TestAppletRuntime" name="Java applet" height="400" width="600">
      <param name="testParams" value="-XX:+PrintHeapAtGC"/>
      <param name="myName" value="SecureArgUntrusted"/>
    </applet-desc>
</jnlp>

After JnlpDownloadServlet's processing it becomes
<?xml version="1.0" encoding="UTF-8"?><jnlp spec="1.0+"codebase="http://127.0.0.1:8080/runtimeArgs/html/" href="RuntimeArgsUnTrustedPrintHeapAtGC.jnlp"> <information> <title>RuntimeArgs Test Applet Demo</title> <vendor>Sun Microsystems, Inc.</vendor> <offline-allowed /> <shortcut online="false"> <desktop/> <menu submenu="Sun Microsystems Applets"/> </shortcut> </information> <resources> <j2se version="1.5+" java-vm-args="-XX:+PrintHeapAtGC"/> <jar href="../classes/test.jar"/> <jar href="../classes/helper.jar"/> </resources> <applet-desc main-class="TestAppletRuntime" name="Java applet" height="400" width="600"> <param name="testParams" value="-XX:+PrintHeapAtGC"/> <param name="myName" value="SecureArgUntrusted"/> </applet-desc></jnlp>

there is no space between "spec" and "codebase" attributes, the jnlp xml is not valid.