GzipResponseStream


1   package com.openedit.servlet.gzip;
2   
3   import java.io.ByteArrayOutputStream  ;
4   import java.io.IOException  ;
5   import java.io.OutputStream  ;
6   import java.util.zip.GZIPOutputStream  ;
7   
8   import javax.servlet.ServletOutputStream  ;
9   import javax.servlet.http.HttpServletResponse  ;
10  
11  public class GzipResponseStream extends ServletOutputStream   {
12    // abstraction of the output stream used for compression
13    protected OutputStream   bufferedOutput = null;
14    // state keeping variable for if close() has been called
15    protected boolean closed = false;
16    // reference to original response
17    protected HttpServletResponse   response = null;
18    // reference to the output stream to the client's browser
19    protected ServletOutputStream   output = null;
20    // default size of the in-memory buffer
21    private int bufferSize = 50000;
22  
23    public GzipResponseStream(HttpServletResponse   response) throws IOException   {
24      super();
25      closed = false;
26      this.response = response;
27      this.output = response.getOutputStream();
28      bufferedOutput = new ByteArrayOutputStream  ();
29    }
30  
31    public void close() throws IOException   {
32      // This hack shouldn't be needed, but it seems to make JBoss and Struts
33      // like the code more without hurting anything.
34      /*
35      // verify the stream is yet to be closed
36      if (closed) {
37        throw new IOException("This output stream has already been closed");
38      }
39      */
40      // if we buffered everything in memory, gzip it
41      if (bufferedOutput instanceof ByteArrayOutputStream  ) {
42        // get the content
43        ByteArrayOutputStream   baos = (ByteArrayOutputStream  )bufferedOutput;
44        // prepare a gzip stream
45        ByteArrayOutputStream   compressedContent = new ByteArrayOutputStream  ();
46        GZIPOutputStream   gzipstream = new GZIPOutputStream  (compressedContent);
47        byte[] bytes = baos.toByteArray();
48        gzipstream.write(bytes);
49        gzipstream.finish();
50        // get the compressed content
51        byte[] compressedBytes = compressedContent.toByteArray();
52        // set appropriate HTTP headers
53        response.setContentLength(compressedBytes.length); 
54        response.addHeader("Content-Encoding", "gzip");
55        output.write(compressedBytes);
56        output.flush();
57        output.close();
58        closed = true;
59      }
60      // if things were not buffered in memory, finish the GZIP stream and response
61      else if (bufferedOutput instanceof GZIPOutputStream  ) {
62        // cast to appropriate type
63        GZIPOutputStream   gzipstream = (GZIPOutputStream  )bufferedOutput;
64        // finish the compression
65        gzipstream.finish();
66        // finish the response
67        output.flush();
68        output.close();
69        closed = true;
70      }
71    }
72  
73    public void flush() throws IOException   {
74      if (closed) {
75        throw new IOException  ("Cannot flush a closed output stream");
76      }
77      bufferedOutput.flush();
78    }
79  
80    public void write(int b) throws IOException   {
81      if (closed) {
82        throw new IOException  ("Cannot write to a closed output stream");
83      }
84      // make sure we aren't over the buffer's limit
85      checkBufferSize(1);
86      // write the byte to the temporary output
87      bufferedOutput.write((byte)b);
88    }
89  
90    private void checkBufferSize(int length) throws IOException   {
91      // check if we are buffering too large of a file
92      if (bufferedOutput instanceof ByteArrayOutputStream  ) {
93        ByteArrayOutputStream   baos = (ByteArrayOutputStream  )bufferedOutput;
94        if (baos.size()+length > bufferSize) {
95          // files too large to keep in memory are sent to the client without Content-Length specified
96          response.addHeader("Content-Encoding", "gzip");
97          // get existing bytes
98          byte[] bytes = baos.toByteArray();
99          // make new gzip stream using the response output stream
100         GZIPOutputStream   gzipstream = new GZIPOutputStream  (output);
101         gzipstream.write(bytes);
102         // we are no longer buffering, send content via gzipstream
103         bufferedOutput = gzipstream;
104       }
105     }
106   }
107   
108   public void write(byte b[]) throws IOException   {
109     write(b, 0, b.length);
110   }
111 
112   public void write(byte b[], int off, int len) throws IOException   {
113     //System.out.println("writing...");
114     if (closed) {
115       throw new IOException  ("Cannot write to a closed output stream");
116     }
117     // make sure we aren't over the buffer's limit
118     checkBufferSize(len);
119     // write the content to the buffer
120     bufferedOutput.write(b, off, len);
121   }
122 
123   public boolean closed() {
124     return (this.closed);
125   }
126   
127   public void reset() {
128     //noop
129   }
130 }
131
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