JavaWeb高级特性书中源代码

package compressionFilters; import java.io.IOException; import java.io.OutputStream; import java.util.zip.GZIPOutputStream; import javax.servlet.ServletOutputStream; import javax.servlet.http.HttpServletResponse; public class CompressionResponseStream extends ServletOutputStream { protected int compressionThreshold = 0; //是否启用压缩的临界值 protected byte[] buffer = null; //临时容纳写入的数据的缓冲区 protected int bufferCount = 0; //缓冲区中实际写如的数据量 protected GZIPOutputStream gzipstream = null; protected boolean closed = false; //当前流对象是否处于关闭状态 protected int length = -1; protected HttpServletResponse response = null; protected ServletOutputStream output = null; public CompressionResponseStream(HttpServletResponse response) throws IOException { super(); closed = false; this.response = response; this.output = response.getOutputStream(); } //设置是否启用压缩的临界值 protected void setBuffer(int threshold) { compressionThreshold = threshold; buffer = new byte[compressionThreshold]; } public void close() throws IOException { if (closed) throw new IOException( "This output stream has already been closed"); /* 根据gzipstream是否为null，就可以知道写入的内容是否达到了 * 启用压缩的临界值，因为达到临界值时，write方法会自动创建 * gzipstream实例对象。 */ if (gzipstream != null) { flushToGZip(); gzipstream.close(); gzipstream = null; } else { if (bufferCount > 0) { output.write(buffer, 0, bufferCount); bufferCount = 0; } } /* 笔者认为这句代码有些问题，如果启用了压缩，在关闭gzipstream流时， * 底层的output流应该自动关闭，所以， * 应该将下句代码放进上面的else从语中 */ output.close(); closed = true; } public void flush() throws IOException { if (closed) { throw new IOException("Cannot flush a closed output stream"); } if (gzipstream != null) { gzipstream.flush(); } } //将buffer缓冲区中的数据写入到gzipstream对象中 public void flushToGZip() throws IOException { if (bufferCount > 0) { writeToGZip(buffer, 0, bufferCount); bufferCount = 0; } } public void write(int b) throws IOException { if (closed) throw new IOException("Cannot write to a closed output stream"); /* 当已经写入的数据达到了启用压缩的临界值时， * 则先将buffer缓冲区中的数据写入到gzipstream对象中 */ if (bufferCount >= buffer.length) { flushToGZip(); } buffer[bufferCount++] = (byte) b; } 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"); if (len == 0) return; /* 如果buffer缓冲区中剩余的空间能够容纳要写入的数据， * 则先将这些数据写入到buffer缓冲区中 */ if (len <= (buffer.length - bufferCount)) { System.arraycopy(b, off, buffer, bufferCount, len); bufferCount += len; return; } /* 如果buffer缓冲区中剩余的空间不能够容纳要写入的数据， * 则先将buffer缓冲区中原有的数据写入到gzipstream对象中 */ flushToGZip(); /* 腾空buffer缓冲区中原有的数据后，判断整个buffer缓冲区是否能够 * 容纳要写入的数据，如果能，将这些数据写入到buffer缓冲区中 */ if (len <= (buffer.length - bufferCount)) { System.arraycopy(b, off, buffer, bufferCount, len); bufferCount += len; return; } /* 如果整个buffer缓冲区的空间都不能够容纳要写入的数据， * 则直接将这些数据写入到gzipstream对象中 */ writeToGZip(b, off, len); } /* 向gzipstream对象中写入数据，如果是第一次写入， * 则还需要首先创建出gzipstream实例对象*/ public void writeToGZip(byte b[], int off, int len) throws IOException { if (gzipstream == null) { response.addHeader("Content-Encoding", "gzip"); gzipstream = new GZIPOutputStream(output); } gzipstream.write(b, off, len); } /* ServletOutputStream类与OutputStream类中都没有定义closed这个方法， * 不知这里为何实现这一个方法，笔者看来纯属多余 */ public boolean closed() { return (this.closed); } }