通过Filter和HttpServletResponseWrapper，实现Gzip压缩

实现定制输出的关键是对HttpServletResponse进行包装，截获所有输出，等过滤器链处理完后，

Filter.doFilter，在截获输出进行处理，在写入到真正的HttpServletResponse中。J2EE中已有

HttpServletResponseWrapper，使得包装HttpServletResponse更加容易

public class GZipFilter implements Filter {

public void destroy() {

}

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException,

ServletException {

HttpServletResponse resp = (HttpServletResponse) response;

Wrapper wrapper = new Wrapper(resp);

chain.doFilter(request, wrapper);

byte[] gzipData = gzip(wrapper.getResponseData());

resp.addHeader("Content-Encoding", "gzip");

resp.setContentLength(gzipData.length);

ServletOutputStream output = response.getOutputStream();

output.write(gzipData);

output.flush();

}

private byte[] gzip(byte[] data) {

ByteArrayOutputStream byteOutput = new ByteArrayOutputStream(10240);

GZIPOutputStream output = null;

try {

output = new GZIPOutputStream(byteOutput);

output.write(data);

} catch (IOException e) {

e.printStackTrace();

} finally {

if (output != null) {

try {

output.close();

} catch (IOException e) {

}

}

}

return byteOutput.toByteArray();

}

public void init(FilterConfig fConfig) throws ServletException {

}

}

类Wrapper:

public class Wrapper extends HttpServletResponseWrapper {

public static final int OT_NONE = 0, OT_WRITER = 1, OT_STREAM = 2;

private int outputType = OT_NONE;

private ServletOutputStream output = null;

private PrintWriter writer = null;

private ByteArrayOutputStream buffer = null;

public Wrapper(HttpServletResponse resp) throws IOException {

super(resp);

buffer = new ByteArrayOutputStream();

}

public PrintWriter getWriter() throws IOException {

if (outputType == OT_STREAM)

throw new IllegalStateException();

else if (outputType == OT_WRITER)

return writer;

else {

outputType = OT_WRITER;

writer = new PrintWriter(new OutputStreamWriter(buffer, getCharacterEncoding()));

return writer;

}

}

public ServletOutputStream getOutputStream() throws IOException {

if (outputType == OT_WRITER)

throw new IllegalStateException();

else if (outputType == OT_STREAM)

return output;

else {

outputType = OT_STREAM;

output = new WrappedOutputStream(buffer);

return output;

}

}

public void flushBuffer() throws IOException {

if (outputType == OT_WRITER)

writer.flush();

if (outputType == OT_STREAM)

output.flush();

}

public void reset() {

outputType = OT_NONE;

buffer.reset();

}

public byte[] getResponseData() throws IOException {

flushBuffer();

return buffer.toByteArray();

}

//内部类，扩展ServletOutputStream

class WrappedOutputStream extends ServletOutputStream {

private ByteArrayOutputStream buffer;

public WrappedOutputStream(ByteArrayOutputStream buffer) {

this.buffer = buffer;

}

public void write(int b) throws IOException {

buffer.write(b);

}

public byte[] toByteArray() {

return buffer.toByteArray();

}

}

}