【发布时间】：2012-02-12 11:33:41
【问题描述】：
我目前正在尝试编写一个自定义流代理（让我们以这种方式调用它），它可以更改给定输入流的内容，并在必要时生成修改后的输出。这个要求真的很有必要，因为有时我必须修改我的应用程序中的流（例如，真正即时压缩数据）。下面的类非常简单，它使用内部缓冲。
private static class ProxyInputStream extends InputStream {
private final InputStream iStream;
private final byte[] iBuffer = new byte[512];
private int iBufferedBytes;
private final ByteArrayOutputStream oBufferStream;
private final OutputStream oStream;
private byte[] oBuffer = emptyPrimitiveByteArray;
private int oBufferIndex;
ProxyInputStream(InputStream iStream, IFunction<OutputStream, ByteArrayOutputStream> oStreamFactory) {
this.iStream = iStream;
oBufferStream = new ByteArrayOutputStream(512);
oStream = oStreamFactory.evaluate(oBufferStream);
}
@Override
public int read() throws IOException {
if ( oBufferIndex == oBuffer.length ) {
iBufferedBytes = iStream.read(iBuffer);
if ( iBufferedBytes == -1 ) {
return -1;
}
oBufferIndex = 0;
oStream.write(iBuffer, 0, iBufferedBytes);
oStream.flush();
oBuffer = oBufferStream.toByteArray();
oBufferStream.reset();
}
return oBuffer[oBufferIndex++];
}
}
假设我们还有一个示例测试输出流，它只是在每个写入的字节（“abc”->“a b c”）之前添加一个空格字符，如下所示：
private static class SpacingOutputStream extends OutputStream {
private final OutputStream outputStream;
SpacingOutputStream(OutputStream outputStream) {
this.outputStream = outputStream;
}
@Override
public void write(int b) throws IOException {
outputStream.write(' ');
outputStream.write(b);
}
}
还有如下测试方法：
private static void test(final boolean useDeflater) throws IOException {
final FileInputStream input = new FileInputStream(SOURCE);
final IFunction<OutputStream, ByteArrayOutputStream> outputFactory = new IFunction<OutputStream, ByteArrayOutputStream>() {
@Override
public OutputStream evaluate(ByteArrayOutputStream outputStream) {
return useDeflater ? new DeflaterOutputStream(outputStream) : new SpacingOutputStream(outputStream);
}
};
final InputStream proxyInput = new ProxyInputStream(input, outputFactory);
final OutputStream output = new FileOutputStream(SOURCE + ".~" + useDeflater);
int c;
while ( (c = proxyInput.read()) != -1 ) {
output.write(c);
}
output.close();
proxyInput.close();
}
此测试方法只是读取文件内容并将其写入另一个流，这可能可以以某种方式进行修改。如果测试方法使用useDeflater=false 运行，则预期的方法可以正常工作。但是如果在 useDeflater 设置为 on 的情况下调用测试方法，它的行为会非常奇怪并且几乎什么都不写（如果省略标题 78 9C）。我怀疑 deflate 类的设计可能不符合我喜欢使用的方法，但我始终相信 ZIP 格式和 deflate 压缩旨在即时工作。
可能我在某些时候对 deflate 压缩算法的细节有误。我真的想念什么？..也许可以有另一种方法来编写“流代理”以完全按照我想要的方式工作...如何动态压缩数据，仅限于流？
提前致谢。
UPD：以下基本版本非常适合 deflater 和 inflater：
public final class ProxyInputStream<OS extends OutputStream> extends InputStream {
private static final int INPUT_BUFFER_SIZE = 512;
private static final int OUTPUT_BUFFER_SIZE = 512;
private final InputStream iStream;
private final byte[] iBuffer = new byte[INPUT_BUFFER_SIZE];
private final ByteArrayOutputStream oBufferStream;
private final OS oStream;
private final IProxyInputStreamListener<OS> listener;
private byte[] oBuffer = emptyPrimitiveByteArray;
private int oBufferIndex;
private boolean endOfStream;
private ProxyInputStream(InputStream iStream, IFunction<OS, ByteArrayOutputStream> oStreamFactory, IProxyInputStreamListener<OS> listener) {
this.iStream = iStream;
oBufferStream = new ByteArrayOutputStream(OUTPUT_BUFFER_SIZE);
oStream = oStreamFactory.evaluate(oBufferStream);
this.listener = listener;
}
public static <OS extends OutputStream> ProxyInputStream<OS> proxyInputStream(InputStream iStream, IFunction<OS, ByteArrayOutputStream> oStreamFactory, IProxyInputStreamListener<OS> listener) {
return new ProxyInputStream<OS>(iStream, oStreamFactory, listener);
}
@Override
public int read() throws IOException {
if ( oBufferIndex == oBuffer.length ) {
if ( endOfStream ) {
return -1;
} else {
oBufferIndex = 0;
do {
final int iBufferedBytes = iStream.read(iBuffer);
if ( iBufferedBytes == -1 ) {
if ( listener != null ) {
listener.afterEndOfStream(oStream);
}
endOfStream = true;
break;
}
oStream.write(iBuffer, 0, iBufferedBytes);
oStream.flush();
} while ( oBufferStream.size() == 0 );
oBuffer = oBufferStream.toByteArray();
oBufferStream.reset();
}
}
return !endOfStream || oBuffer.length != 0 ? (int) oBuffer[oBufferIndex++] & 0xFF : -1;
}
}
【问题讨论】：
-
我有点失落。但是当我不想压缩时，我应该简单地使用原始的
outputStream，而当我想要压缩时使用new GZipOutputStream(outputStream)。就这样。无论如何，请检查您是否正在刷新输出流。 -
ByteArrayOutputStream!=BufferedOutputStream。非常喜欢。
标签： java stream zip deflate on-the-fly