Java tutorial
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/* $Id: SubInputStream.java 604883 2007-12-17 14:36:37Z jeremias $ */
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
/**
* This class is a FilterInputStream descendant that reads from an underlying InputStream
* up to a defined number of bytes or the end of the underlying stream. Closing this InputStream
* will not result in the underlying InputStream to be closed, too.
* <p>
* This InputStream can be used to read chunks from a larger file of which the length is
* known in advance.
*/
public class SubInputStream extends FilterInputStream {
/** Indicates the number of bytes remaining to be read from the underlying InputStream. */
private long bytesToRead;
/**
* Indicates whether the underlying stream should be closed when the {@link #close()} method
* is called.
*/
private boolean closeUnderlying = false;
/**
* Creates a new SubInputStream.
* @param in the InputStream to read from
* @param maxLen the maximum number of bytes to read from the underlying InputStream until
* the end-of-file is signalled.
* @param closeUnderlying true if the underlying stream should be closed when the
* {@link #close()} method is called.
*/
public SubInputStream(InputStream in, long maxLen, boolean closeUnderlying) {
super(in);
this.bytesToRead = maxLen;
this.closeUnderlying = closeUnderlying;
}
/**
* Creates a new SubInputStream. The underlying stream is not closed, when close() is called.
* @param in the InputStream to read from
* @param maxLen the maximum number of bytes to read from the underlying InputStream until
* the end-of-file is signalled.
*/
public SubInputStream(InputStream in, long maxLen) {
this(in, maxLen, false);
}
/** {@inheritDoc} */
public int read() throws IOException {
if (bytesToRead > 0) {
int result = super.read();
if (result >= 0) {
bytesToRead--;
return result;
} else {
return -1;
}
} else {
return -1;
}
}
/** {@inheritDoc} */
public int read(byte[] b, int off, int len) throws IOException {
if (bytesToRead == 0) {
return -1;
}
int effRead = (int) Math.min(bytesToRead, len);
//cast to int is safe because len can never be bigger than Integer.MAX_VALUE
int result = super.read(b, off, effRead);
if (result >= 0) {
bytesToRead -= result;
}
return result;
}
/** {@inheritDoc} */
public long skip(long n) throws IOException {
long effRead = Math.min(bytesToRead, n);
long result = super.skip(effRead);
bytesToRead -= result;
return result;
}
/** {@inheritDoc} */
public void close() throws IOException {
this.bytesToRead = 0;
if (this.closeUnderlying) {
super.close();
}
}
}
//////////////////////////////////
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/* $Id: SubInputStreamTestCase.java 604883 2007-12-17 14:36:37Z jeremias $ */
package org.apache.xmlgraphics.util.io;
import java.io.ByteArrayInputStream;
import java.util.Arrays;
import junit.framework.TestCase;
/**
* Test case for SubInputStream.
*/
public class SubInputStreamTestCase extends TestCase {
/**
* Main constructor.
* @param name the test case's name
* @see junit.framework.TestCase#TestCase(String)
*/
public SubInputStreamTestCase(String name) {
super(name);
}
/**
* Tests SubInputStream.
* @throws Exception if an error occurs
*/
public void testMain() throws Exception {
//Initialize test data
byte[] data = new byte[256];
for (int i = 0; i < data.length; i++) {
data[i] = (byte) (i & 0xff);
}
int v, c;
byte[] buf;
String s;
SubInputStream subin = new SubInputStream(new ByteArrayInputStream(data), 10);
v = subin.read();
assertEquals(0, v);
v = subin.read();
assertEquals(1, v);
buf = new byte[4];
c = subin.read(buf);
assertEquals(4, c);
s = new String(buf, "US-ASCII");
assertEquals("\u0002\u0003\u0004\u0005", s);
Arrays.fill(buf, (byte) 0);
c = subin.read(buf, 2, 2);
assertEquals(2, c);
s = new String(buf, "US-ASCII");
assertEquals("\u0000\u0000\u0006\u0007", s);
Arrays.fill(buf, (byte) 0);
c = subin.read(buf);
assertEquals(2, c);
s = new String(buf, "US-ASCII");
assertEquals("\u0008\u0009\u0000\u0000", s);
}
}