• Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 478
  • Last Modified:

Java: Trying to log a string to file, but it doesn't work

Hi Guys - I'm creating a program that has a need to log HTTP traffic.  The traffic is read from socket to buffer to string.  Then the below method is invoked to write that string to file.  The code is pretty straight forward.

It uses java.io.filewriter to do the work.  filewriter has a method - write() that takes a String as an argument and according to the JavaDocs, should write it to the file linked to the filewriter.

The File object referenced (request) is created as a global variable, so the file exists.  When I compile and run the code, the file gets created and my debug shos that the method and proper code is being invoked, yet the file is empty.

Am I not using the FileWriter correctly?  What could be the problem?  Maybe there is a better way to do this?

In case you plan to suggest using Apache Commons, please don't - I can't use it for this project.
private void logIt(String toWrite, int a) throws IOException
    {
        //Determine if we are logging Client request traffic
        //or server reply traffic
        if (a == 0){
            FileWriter writer = new FileWriter(request, true);
            //Write to requestlog.txt
            writer.write(toWrite);
            debug("Client Request traffic logged");
        }else {
            //Write to requestlog.txt
            FileWriter writer = new FileWriter(reply, true);
            writer.write(toWrite);
            debug("Server Reply traffic logged");
        }
    }

Open in new window

0
southpau1
Asked:
southpau1
  • 5
  • 4
2 Solutions
 
CEHJCommented:
You need to close the Writer each time
0
 
objectsCommented:
you need to close the writer
0
 
objectsCommented:
you'll also find it simpler to use a PrintWriter


            PrintWriter writer = new PrintWriter(new FileWriter(reply, true));
            writer.println(toWrite);
            writer.close();
0
Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

 
southpau1Author Commented:
Ok that worked!  I close and it logs.  But now I get these errors and my entire program doesn't work..
java.lang.NullPointerException
	at java.io.Writer.write(Writer.java:140)
	at com.mba.proxylight.RequestProcessor.logIt(RequestProcessor.java:421)
	at com.mba.proxylight.RequestProcessor.access$1400(RequestProcessor.java:24)
	at com.mba.proxylight.RequestProcessor$RequestProcessorRunner.processChannel(RequestProcessor.java:237)
	at com.mba.proxylight.RequestProcessor$RequestProcessorRunner.run(RequestProcessor.java:121)
	at java.lang.Thread.run(Thread.java:662)

Open in new window

0
 
CEHJCommented:
You're calling write without initializing the Writer again
0
 
objectsCommented:
looks like you're passing null to your logit method, should test for that

if (request!=null) {
        if (a == 0){
            PrintWriter writer = new PrintWriter(new FileWriter(request, true));
            writer.println(toWrite);
            writer.close();
            debug("Client Request traffic logged");
        }else {
            PrintWriter writer = new PrintWriter(new FileWriter(reply, true));
            writer.println(toWrite);
            writer.close();
            debug("Server Reply traffic logged");
        }
}
0
 
objectsCommented:
you can also simplify that a little

      if (toWrite!=null) {
            PrintWriter writer = new PrintWriter(new FileWriter(a==0 ? request : reply), true));
            writer.println(toWrite);
            writer.close();
      }
0
 
CEHJCommented:
Try
private void logIt(String toWrite, int a) throws IOException {
        //Determine if we are logging Client request traffic
        //or server reply traffic
        FileWriter writer = null;

        try {
            if (a == 0) {
                writer = new FileWriter(request, true);
                //Write to requestlog.txt
                writer.write(toWrite);
                debug("Client Request traffic logged");
            } else {
                //Write to requestlog.txt
                writer = new FileWriter(reply, true);
                writer.write(toWrite);
                debug("Server Reply traffic logged");
            }
        } finally {
            try {
                writer.close();
            } catch (Exception e) { /* ignore */
            }
        }
    }

Open in new window

0
 
CEHJCommented:
Don't hide/trap null pointers. Find out why null is being passed if it is and change it
0
 
CEHJCommented:
:)
0
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

Featured Post

Get your problem seen by more experts

Be seen. Boost your question’s priority for more expert views and faster solutions

  • 5
  • 4
Tackle projects and never again get stuck behind a technical roadblock.
Join Now