使用Java中的BufferedReader读取整个char流

Question

I am programming a simple AJAX application that's taking input from a form on a JSP and then using JSON to pass the data to a servlet. In the servlet, I have the following quick and dirty code:

    char[] charBuffer = new char[500];
    String[] names;
    String[] values = new String[20];
    int amountRead;

    JSONObject jsonObject1;
    JSONObject jsonObject2;

    PrintWriter out = response.getWriter();
    BufferedReader in = request.getReader();

    amountRead = in.read(charBuffer);

    charBuffer[amountRead]='\0';
    String invalue = new String( charBuffer, 0, amountRead);

This is all then followed by a try block that does some stuff with the JSON objects. Basically, as an exercise, I am trying to pass the same form data back and forth and display it.

Here is the problem: In this quick and dirty code, of course, there's no guarantee that you get the full message from the request. Knowing that the read() method of BufferedReader will return -1 if the end of the stream has been reached, I've tried making the following addition:

    while( in.read() != -1 ) {
         amountRead = in.read(charBuffer); 
    }

Once I implement this, however, my output is blank. I'm just getting nothing. Even after trying to step through it with the debugger, I'm not entirely sure why that while loop isn't having the intended effect.

I'm sure it's something simple and stupid. Could somebody be so kind as to point out the error of my ways? As always, thanks in advance.

Answer 1

You're reading a char then throwing it away if you didn't get EOS. The correct way to read streams in Java is like this:

while ((count = in.read(buffer)) > 0)
{
   out.write(buffer, 0, count);
   // or
   String s = new String(buffer, 0, count);
   // or whatever else you want.
}

Your insertion of a trailing null character is unnecessary, too. That's a C-ism. You're already bounding the string by specifying the count, so the null character is never even seen.

Answer 2

The BufferedReader.readLine() method will read exactly one line at a time and each read will block until the data is available. It'll return null when the end of the stream has been reached.

So in a while loop you can use

String line;
BuffererReader br = request.getReader();
while ((line = br.readLine()) != null) { 
    //process the line here
}

You can also use a library like Gson which can deserialise a Java class from a Reader for you.