Migrate Java code to separate QL repo.

java/ql/src/Performance/InefficientOutputStreamGood.java

@@ -0,0 +1,32 @@
+public class DigestCheckingFileOutputStream extends OutputStream {
+	private DigestOutputStream digest;
+	private byte[] expectedMD5;
+
+	public DigestCheckingFileOutputStream(File file, byte[] expectedMD5)
+		throws IOException, NoSuchAlgorithmException {
+			this.expectedMD5 = expectedMD5;
+			digest = new DigestOutputStream(new FileOutputStream(file),
+											MessageDigest.getInstance("MD5"));
+		}
+
+	@Override
+	public void write(int b) throws IOException {
+		digest.write(b);
+	}
+
+	@Override
+	public void write(byte[] b, int off, int len) throws IOException {
+		digest.write(b, off, len);
+	}
+
+	@Override
+	public void close() throws IOException {
+		super.close();
+
+		digest.close();
+		byte[] md5 = digest.getMessageDigest().digest();
+		if (expectedMD5 != null && !Arrays.equals(expectedMD5, md5)) {
+			throw new InternalError();
+		}
+	}
+}