Closing Streams

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Most streams must be closed when you are done with them, otherwise you could introduce a memory leak or leave a file open. It is important that streams are closed even if an exception is thrown.

try(FileWriter fw = new FileWriter("outfilename");
    BufferedWriter bw = new BufferedWriter(fw);
    PrintWriter out = new PrintWriter(bw))
{
    out.println("the text");
    //more code
    out.println("more text");
    //more code
} catch (IOException e) {
    //handle this however you 
}

Remember: try-with-resources guarantees, that the resources have been closed when the block is exited, whether that happens with the usual control flow or because of an exception.

Sometimes, try-with-resources is not an option, or maybe you’re supporting older version of Java 6 or earlier. In this case, proper handling is to use a finally block:

FileWriter fw = null;
BufferedWriter bw = null;
PrintWriter out = null;
try {
    fw = new FileWriter("myfile.txt");
    bw = new BufferedWriter(fw);
    out = new PrintWriter(bw);
    out.println("the text");
    out.close();
} catch (IOException e) {
    //handle this however you want
}
finally {
    try {
        if(out != null)
            out.close();
    } catch (IOException e) {
        //typically not much you can do here...
    }
}

Note that closing a wrapper stream will also close its underlying stream. This means you cannot wrap a stream, close the wrapper and then continue using the original stream.

Found a mistake? Have a question or improvement idea? Let me know.

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