Rule Definition
A frequent issue when dealing with stream is resource leak. This mainly comes from an incorrect code that miss to close the stream in any cases. Incorrect resource management is a common source of failures in production applications, with the usual pitfalls being database connections and file descriptors remaining opened after an exception has occurred somewhere else in the code. This leads to application servers being frequently restarted when resource exhaustion occurs, because operating systems and server applications generally have an upper-bound limit for resources.

Remediation
You can: - use the try with resource to declare the resource that must be closed (available in java 7) - or close the resource in a finally block. - or annotate this resource with @Cleanup annotation (lombok.Cleanup)

Violation Code Sample

private void incorrectWriting() throws IOException {
    DataOutputStream out = new DataOutputStream(new FileOutputStream("data"));
    out.writeInt(666);
    out.writeUTF("Hello");
    out.close();
} // VIOLATION

Fixed Code Sample

with finally
~~~~~~~~~~~~   
private void correctWriting() throws IOException {
    DataOutputStream out = null;
    try {
        out = new DataOutputStream(new FileOutputStream("data"));
        out.writeInt(666);
        out.writeUTF("Hello");
    } finally {
        if (out != null) {
            out.close(); // FIX
        }
    }        
}

with Java 7
~~~~~~~~~~~
private void writingWithARM() throws IOException {
    try (DataOutputStream out 
            = new DataOutputStream(new FileOutputStream("data"))) { // FIX
        out.writeInt(666);
        out.writeUTF("Hello");
    }
}

with @Cleanup annotation
~~~~~~~~~~~~~~~~~~~~~~~~
private void writingWithCleanup() throws IOException {
    @Cleanup DataOutputStream out = new DataOutputStream(new FileOutputStream("data")); // FIX
    out.writeInt(666);
    out.writeUTF("Hello");
}

http://stackoverflow.com/questions/15405396/is-it-necessary-to-close-input-output-streams-created-from-a-sockets-io-streams http://www.oracle.com/technetwork/articles/java/trywithresources-401775.html