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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),它可以改变给定输入流中的内容,并在必要时生成修改后的输出.这个要求确实是必要的,因为有时我必须修改我的应用程序中的流(例如,在运行中真正压缩数据).以下类非常简单,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);
}
}
以下测试方法：
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,这可能会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设置的情况下调用测试方法,它的行为非常奇怪,并且几乎不写任何内容(如果省略标题78 9C).我怀疑deflater类的设计可能不符合我喜欢使用的方法,但我一直认为ZIP格式和deflate压缩设计是为了在飞行中工作.
可能我在某种程度上对于deflate压缩算法的细节是错误的.我真正想念的是什么？也许可能有另一种方法来编写“流代理”,以完全按照我希望它的工作方式行事……我如何仅仅使用流来限制数据的压缩？
提前致谢.
UPD：以下基本版本与deflater和inflater相当不错：
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;
}
} 解决方法: 我不相信DeflaterOutputStream.flush()做任何有意义的事情. deflater将累积数据,直到它有东西写出到底层流.强制剩余数据输出的唯一方法是调用DeflaterOutputStream.finish().但是,这对您当前的实现不起作用,因为在您完成写作之前无法调用完成.
实际上编写压缩流并在同一个线程中读取它实际上非常困难.在RMIIO项目中,我实际上是这样做的,但是你需要一个任意大小的中间输出缓冲区(你基本上需要将数据推入,直到另一端压缩出来的东西,然后你就可以读取它).您可以使用该项目中的某些util类来完成您想要执行的操作. 来源：http://www./content-1-235351.html
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