In trying to get to know the HttpClient component a bit, I attempted to write a simple
program using a Java Servlet and the HttpClient API - the end result being that the
client make a post to the servlet and the servlet return a brief HTML response to the
client. The next step would be to transfer a file between the two, however, I'm
running into some trouble with this first step.
The only real requirements I've placed on this step is to use a post method instead of
a get (because future steps would not be able to use a get), and to pass a parameter
in the request. The parameter is where my problems start. After checking for this
parameter on the server side, I throw an exception if it is non-existent. This is as
far as the program has been running for me.
I'm using HTTP Client 2.0 Alpha 2, and Commons Logging 1.0.2. I've included a couple
of example classes that represent the basics of my code, and the thrown exception, in
case anyone might have an idea as to what I am doing wrong:
_________________________________________________________________________________________________
CLIENT CLASS -
import org.apache.commons.httpclient.*;
import org.apache.commons.httpclient.methods.*;
import java.io.*;
import java.net.*;
public class HttpClientExmpl
{
public HttpClientExmpl()
{
init();
}
public void init()
{
MultipartPostMethod postMethod = new MultipartPostMethod();
postMethod.setPath("/servlet/HttpClientExmplServlet");
postMethod.addParameter("param-name", "param-value");
HttpClient client = new HttpClient();
HostConfiguration hostConfig = new HostConfiguration();
hostConfig.setHost("localhost", 8081, "http");
client.setConnectionTimeout(30000);
client.setHostConfiguration(hostConfig);
try
{
client.executeMethod(postMethod);
}
catch(HttpException httpEx)
{
httpEx.printStackTrace();
}
catch(IOException ioEx)
{
ioEx.printStackTrace();
}
String responseString = postMethod.getResponseBodyAsString();
postMethod.releaseConnection();
System.out.println(responseString);
}
public static void main(String args[])
{
new HttpClientExmpl();
}
}
_________________________________________________________________________________________________
SERVLET CLASS -
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
public class HttpClientExmplServlet extends HttpServlet
{
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
String paramValue = request.getParameter("param-name");
if(paramValue == null)
throw new ServletException(new NullPointerException("The getParameter call
returned null."));
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
StringBuffer buf = new StringBuffer();
buf.append("<HTML>\n");
buf.append("<HEAD>\n<TITLE>HTTP Client Example
Application</TITLE>\n</HEAD>\n");
buf.append("<BODY>\n");
buf.append("The servlet received the parameter sent within the post
method.\n");
buf.append("</BODY>\n");
buf.append("</HTML>");
writer.write(buf.toString());
writer.flush();
writer.close();
}
}
_________________________________________________________________________________________________
RESULTING EXCEPTION -
2003-01-27 21:08:27 StandardWrapperValve[HttpClientExmplServlet]: Servlet.service()
for servlet HttpClientExmplServlet threw exception
java.lang.NullPointerException: The getParameter call returned null.
at HttpClientExmplServlet.doPost(HttpClientExmplServlet.java:14)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:760)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:223)
at
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:213)
at
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:243)
at
org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
at
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:190)
at
org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
at
org.apache.catalina.valves.CertificatesValve.invoke(CertificatesValve.java:246)
at
org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
at
org.netbeans.modules.web.monitor.catalina.MonitorValve.invoke(MonitorValve.java:142)
at
org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2347)
at
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
at
org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
at
org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:170)
at
org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
at
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:170)
at
org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:468)
at
org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
at
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
at
org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
at
org.apache.catalina.connector.http.HttpProcessor.process(HttpProcessor.java:1027)
at
org.apache.catalina.connector.http.HttpProcessor.run(HttpProcessor.java:1125)
at java.lang.Thread.run(Thread.java:536)
Any suggestions would be greatly appreciated.
Thanks,
Daniel
p.s. I'm not even sure that MultipartPostMethod is the most suitable object for this.
If not, I'd appreciate a point in the right direction.
