Question

I’m messing about with Java, after a long hiatus, and I’m running into my usual problems with its complexity.

I have what should be a simple problem, but what with InputStreams, InputReaders, and dealing with finally and close(), I’m not seeing an obvious answer.

I’m in the main() function of a simple command-line app. I’ve parsed my command-line, and I have a input filename. This contains either the path to a text file or “-“, which means that the program should read from System.in.

What I want is a String containing the contents of the file (or the remaining contents of System.in). And what I am ending up with is way too complex, so I’m looking for the simple way to do it.

Question 1: Given an InputStream (which might be System.in or it might be a FileInputStream() I opened myself, what’s the simplest way to read all of its contents into a String? The various readAll() methods I’ve been seeing returned byte arrays, for which there is a place, but it’s not what I am looking for.

Question 2: What is the usual idiom for making sure that any reader I open will always be closed?

If I were writing in C++, I’d have put the close() in my class’s destructor, and I’d be sure that close() would be called when my object fell out of scope.

If I were writing in C#, I’d have used a “using” block, and I’d have the same guarantee.

I’m sure this can be done in Java, but my attempts so far have seemed cumbersome.

If I try:

try
{
    InputStream inStream = new InputStream(...);
}
finally
{
    inStream.close();
}

I get complains that “inStream cannot be resolved”.

But if I try

InputStream inStream = null;
try
{
    inStream = new InputStream(...);
}
finally
{
    if (inStream != null)
        inStream.close();
}

I get “Unhandled exception type IOException.

So now I’m at:

InputStream inStream = null;
try
{
    inStream = new InputStream(...);
}
finally
{
    try
    {
        if (inStream != null)
            inStream.close();
    }
    catch (IOException ex)
    {
    }
}

And that just seems ludicrous.

What is the usual pattern?

Answer 1

You might want to try using Apache Commons IO to wrap some of this stuff for you. An example:

import org.apache.commons.io.FileUtils;

File f = new File("mystuff.txt");
String contents = FileUtils.readFileToString(f);

Or, if you’re starting with a stream:

import org.apache.commons.io.IOUtils;

InputStream is = new InputStream(...);
String contents = IOUtils.toString(is);

And much, much more :-).