gzipresponsestream.java

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package org.appfuse.webapp.filter;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.zip.GZIPOutputStream;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;


/**
 * Wraps Response Stream for GZipFilter
 *
 * @author  Matt Raible
 * @version $Revision: 1.3 $ $Date: 2004/05/16 02:17:00 $
 */
public class GZIPResponseStream extends ServletOutputStream {
    // abstraction of the output stream used for compression
    protected OutputStream bufferedOutput = null;

    // state keeping variable for if close() has been called
    protected boolean closed = false;

    // reference to original response
    protected HttpServletResponse response = null;

    // reference to the output stream to the client's browser
    protected ServletOutputStream output = null;

    // default size of the in-memory buffer
    private int bufferSize = 50000;

    public GZIPResponseStream(HttpServletResponse response)
    throws IOException {
        super();
        closed = false;
        this.response = response;
        this.output = response.getOutputStream();
        bufferedOutput = new ByteArrayOutputStream();
    }

    public void close() throws IOException {
        // verify the stream is yet to be closed
        if (closed) {
            throw new IOException("This output stream has already been closed");
        }

        // if we buffered everything in memory, gzip it
        if (bufferedOutput instanceof ByteArrayOutputStream) {
            // get the content
            ByteArrayOutputStream baos = (ByteArrayOutputStream) bufferedOutput;

            // prepare a gzip stream
            ByteArrayOutputStream compressedContent =
                new ByteArrayOutputStream();
            GZIPOutputStream gzipstream =
                new GZIPOutputStream(compressedContent);
            byte[] bytes = baos.toByteArray();
            gzipstream.write(bytes);
            gzipstream.finish();

            // get the compressed content
            byte[] compressedBytes = compressedContent.toByteArray();

            // set appropriate HTTP headers
            response.setContentLength(compressedBytes.length);
            response.addHeader("Content-Encoding", "gzip");
            output.write(compressedBytes);
            output.flush();
            output.close();
            closed = true;
        }
        // if things were not buffered in memory, finish the GZIP stream and response
        else if (bufferedOutput instanceof GZIPOutputStream) {
            // cast to appropriate type
            GZIPOutputStream gzipstream = (GZIPOutputStream) bufferedOutput;

            // finish the compression
            gzipstream.finish();

            // finish the response
            output.flush();
            output.close();
            closed = true;
        }
    }

    public void flush() throws IOException {
        if (closed) {
            throw new IOException("Cannot flush a closed output stream");
        }

        bufferedOutput.flush();
    }

    public void write(int b) throws IOException {
        if (closed) {
            throw new IOException("Cannot write to a closed output stream");
        }

        // make sure we aren't over the buffer's limit
        checkBufferSize(1);

        // write the byte to the temporary output
        bufferedOutput.write((byte) b);
    }

    private void checkBufferSize(int length) throws IOException {
        // check if we are buffering too large of a file
        if (bufferedOutput instanceof ByteArrayOutputStream) {
            ByteArrayOutputStream baos = (ByteArrayOutputStream) bufferedOutput;

            if ((baos.size() + length) > bufferSize) {
                // files too large to keep in memory are sent to the client without Content-Length specified
                response.addHeader("Content-Encoding", "gzip");

                // get existing bytes
                byte[] bytes = baos.toByteArray();

                // make new gzip stream using the response output stream
                GZIPOutputStream gzipstream = new GZIPOutputStream(output);
                gzipstream.write(bytes);

                // we are no longer buffering, send content via gzipstream
                bufferedOutput = gzipstream;
            }
        }
    }

    public void write(byte[] b) throws IOException {
        write(b, 0, b.length);
    }

    public void write(byte[] b, int off, int len) throws IOException {

        if (closed) {
            throw new IOException("Cannot write to a closed output stream");
        }

        // make sure we aren't over the buffer's limit
        checkBufferSize(len);

        // write the content to the buffer
        bufferedOutput.write(b, off, len);
    }

    public boolean closed() {
        return (this.closed);
    }

    public void reset() {
        //noop
    }
}