我尝试将InputStream复制到File，如果InputStream的大小大于1MB，则中止复制。 在Java7中，我编写了如下代码：
public void copy(InputStream input, Path target) {
OutputStream out = Files.newOutputStream(target,
StandardOpenOption.CREATE_NEW, StandardOpenOption.WRITE);
boolean isExceed = false;
try {
long nread = 0L;
byte[] buf = new byte[BUFFER_SIZE];
int n;
while ((n = input.read(buf)) > 0) {
out.write(buf, 0, n);
nread += n;
if (nread > 1024 * 1024) {// Exceed 1 MB
isExceed = true;
break;
}
}
} catch (IOException ex) {
throw ex;
} finally {
out.close();
if (isExceed) {// Abort the copy
Files.deleteIfExists(target);
throw new IllegalArgumentException();
}
}}
ByteArrayOutputStream，然后获取size()。但问题是InputStream可能不是markSupported()，因此无法在复制文件操作中重用InputStream。答案 0 :(得分：16)
我个人的选择是一个InputStream包装器，它在读取字节时对字节进行计数：
public class LimitedSizeInputStream extends InputStream {
private final InputStream original;
private final long maxSize;
private long total;
public LimitedSizeInputStream(InputStream original, long maxSize) {
this.original = original;
this.maxSize = maxSize;
}
@Override
public int read() throws IOException {
int i = original.read();
if (i>=0) incrementCounter(1);
return i;
}
@Override
public int read(byte b[]) throws IOException {
return read(b, 0, b.length);
}
@Override
public int read(byte b[], int off, int len) throws IOException {
int i = original.read(b, off, len);
if (i>=0) incrementCounter(i);
return i;
}
private void incrementCounter(int size) throws IOException {
total += size;
if (total>maxSize) throw new IOException("InputStream exceeded maximum size in bytes.");
}
}
我喜欢这种方法，因为它是透明的，可以与所有输入流重复使用，并且可以很好地与其他库一起使用。例如，使用Apache Commons复制最大4KB的文件：
InputStream in = new LimitedSizeInputStream(new FileInputStream("from.txt"), 4096);
OutputStream out = new FileOutputStream("to.txt");
IOUtils.copy(in, out);
PS：上面的实现与BoundedInputStream的主要区别在于，当超出限制时BoundedInputStream不会抛出异常（它只是关闭流）
答案 1 :(得分：8)
以下是现成的解决方案：
答案 2 :(得分：3)
第一个问题：有没有更好的解决方案？
不是真的。当然，并没有明显更好。
第二个问题：我的另一个解决方案 - 在复制操作之前，我计算InputStream的大小。所以我将InputStream复制到ByteArrayOutputStream然后获取size（）。但问题是InputStream可能没有markSupported（），因此无法在复制文件操作中重用InputStream。
暂且不论以上是陈述不是问题......
如果已将字节复制到ByteArrayOutputStream，则可以从ByteArrayInputStream返回的字节数组中创建baos.toByteArray()。因此，您无需标记/重置原始流。
然而，这是一种非常难看的实现方式。尤其是因为您正在阅读并缓冲整个输入流。
答案 3 :(得分：0)
我喜欢基于ByteArrayOutputStream的解决方案，我无法理解为什么它无法工作
public void copy(InputStream input, Path target) throws IOException {
ByteArrayOutputStream bos = new ByteArrayOutputStream();
BufferedInputStream bis = new BufferedInputStream(input);
for (int b = 0; (b = bis.read()) != -1;) {
if (bos.size() > BUFFER_SIZE) {
throw new IOException();
}
bos.write(b);
}
Files.write(target, bos.toByteArray());
}
答案 4 :(得分：0)
这是Apache Tomcat的实现：
package org.apache.tomcat.util.http.fileupload.util;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
/**
* An input stream, which limits its data size. This stream is
* used, if the content length is unknown.
*/
public abstract class LimitedInputStream extends FilterInputStream implements Closeable {
/**
* The maximum size of an item, in bytes.
*/
private final long sizeMax;
/**
* The current number of bytes.
*/
private long count;
/**
* Whether this stream is already closed.
*/
private boolean closed;
/**
* Creates a new instance.
*
* @param inputStream The input stream, which shall be limited.
* @param pSizeMax The limit; no more than this number of bytes
* shall be returned by the source stream.
*/
public LimitedInputStream(InputStream inputStream, long pSizeMax) {
super(inputStream);
sizeMax = pSizeMax;
}
/**
* Called to indicate, that the input streams limit has
* been exceeded.
*
* @param pSizeMax The input streams limit, in bytes.
* @param pCount The actual number of bytes.
* @throws IOException The called method is expected
* to raise an IOException.
*/
protected abstract void raiseError(long pSizeMax, long pCount)
throws IOException;
/**
* Called to check, whether the input streams
* limit is reached.
*
* @throws IOException The given limit is exceeded.
*/
private void checkLimit() throws IOException {
if (count > sizeMax) {
raiseError(sizeMax, count);
}
}
/**
* Reads the next byte of data from this input stream. The value
* byte is returned as an <code>int</code> in the range
* <code>0</code> to <code>255</code>. If no byte is available
* because the end of the stream has been reached, the value
* <code>-1</code> is returned. This method blocks until input data
* is available, the end of the stream is detected, or an exception
* is thrown.
* <p>
* This method
* simply performs <code>in.read()</code> and returns the result.
*
* @return the next byte of data, or <code>-1</code> if the end of the
* stream is reached.
* @throws IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
@Override
public int read() throws IOException {
int res = super.read();
if (res != -1) {
count++;
checkLimit();
}
return res;
}
/**
* Reads up to <code>len</code> bytes of data from this input stream
* into an array of bytes. If <code>len</code> is not zero, the method
* blocks until some input is available; otherwise, no
* bytes are read and <code>0</code> is returned.
* <p>
* This method simply performs <code>in.read(b, off, len)</code>
* and returns the result.
*
* @param b the buffer into which the data is read.
* @param off The start offset in the destination array
* <code>b</code>.
* @param len the maximum number of bytes read.
* @return the total number of bytes read into the buffer, or
* <code>-1</code> if there is no more data because the end of
* the stream has been reached.
* @throws NullPointerException If <code>b</code> is <code>null</code>.
* @throws IndexOutOfBoundsException If <code>off</code> is negative,
* <code>len</code> is negative, or <code>len</code> is greater than
* <code>b.length - off</code>
* @throws IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
@Override
public int read(byte[] b, int off, int len) throws IOException {
int res = super.read(b, off, len);
if (res > 0) {
count += res;
checkLimit();
}
return res;
}
/**
* Returns, whether this stream is already closed.
*
* @return True, if the stream is closed, otherwise false.
* @throws IOException An I/O error occurred.
*/
@Override
public boolean isClosed() throws IOException {
return closed;
}
/**
* Closes this input stream and releases any system resources
* associated with the stream.
* This
* method simply performs <code>in.close()</code>.
*
* @throws IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
@Override
public void close() throws IOException {
closed = true;
super.close();
}
}
您应该对此子类化，并覆盖raiseError方法。
答案 5 :(得分：0)
更方便快捷的解决方案来检查输入流的大小
FileChannel chanel = (FileChannel) Channels.newChannel(inputStream);
MappedByteBuffer buffer = chanel.map(FileChannel.MapMode.READ_ONLY, 0, chanel.size());
System.out.println(buffer.capacity()); // bytes