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Provides a CachingOuptutStream and a CachingWriter (#184)
Provides a CachingOuptutStream and a CachingWriter
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‎src/main/java/org/codehaus/plexus/util/io/CachingOutputStream.java

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package org.codehaus.plexus.util.io;
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/*
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* Copyright The Codehaus Foundation.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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import java.io.File;
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import java.io.IOException;
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import java.io.OutputStream;
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import java.nio.Buffer;
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import java.nio.ByteBuffer;
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import java.nio.channels.FileChannel;
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import java.nio.file.Files;
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import java.nio.file.Path;
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import java.nio.file.StandardOpenOption;
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import java.nio.file.attribute.FileTime;
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import java.time.Instant;
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import java.util.Objects;
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/**
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* Caching OutputStream to avoid overwriting a file with
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* the same content.
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*/
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public class CachingOutputStream extends OutputStream
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{
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private final Path path;
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private FileChannel channel;
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private ByteBuffer readBuffer;
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private ByteBuffer writeBuffer;
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private boolean modified;
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public CachingOutputStream( File path ) throws IOException
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{
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this( Objects.requireNonNull( path ).toPath() );
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}
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public CachingOutputStream( Path path ) throws IOException
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{
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this( path, 32 * 1024 );
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}
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public CachingOutputStream( Path path, int bufferSize ) throws IOException
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{
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this.path = Objects.requireNonNull( path );
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this.channel = FileChannel.open( path,
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StandardOpenOption.READ, StandardOpenOption.WRITE, StandardOpenOption.CREATE );
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this.readBuffer = ByteBuffer.allocate( bufferSize );
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this.writeBuffer = ByteBuffer.allocate( bufferSize );
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}
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@Override
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public void write( int b ) throws IOException
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{
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if ( writeBuffer.remaining() < 1 )
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{
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( ( Buffer ) writeBuffer ).flip();
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flushBuffer( writeBuffer );
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( ( Buffer ) writeBuffer ).clear();
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}
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writeBuffer.put( ( byte ) b );
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}
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@Override
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public void write( byte[] b ) throws IOException
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{
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write( b, 0, b.length );
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}
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@Override
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public void write( byte[] b, int off, int len ) throws IOException
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{
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if ( writeBuffer.remaining() < len )
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{
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( ( Buffer ) writeBuffer ).flip();
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flushBuffer( writeBuffer );
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( ( Buffer ) writeBuffer ).clear();
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}
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int capacity = writeBuffer.capacity();
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while ( len >= capacity )
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{
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flushBuffer( ByteBuffer.wrap( b, off, capacity ) );
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off += capacity;
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len -= capacity;
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}
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if ( len > 0 )
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{
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writeBuffer.put( b, off, len );
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}
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}
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@Override
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public void flush() throws IOException
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{
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( ( Buffer ) writeBuffer ).flip();
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flushBuffer( writeBuffer );
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( ( Buffer ) writeBuffer ).clear();
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super.flush();
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}
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private void flushBuffer( ByteBuffer writeBuffer ) throws IOException
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{
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if ( modified )
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{
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channel.write( writeBuffer );
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}
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else
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{
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int len = writeBuffer.remaining();
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ByteBuffer readBuffer;
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if ( this.readBuffer.capacity() >= len )
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{
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readBuffer = this.readBuffer;
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( ( Buffer ) readBuffer ).clear();
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}
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else
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{
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readBuffer = ByteBuffer.allocate( len );
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}
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while ( len > 0 )
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{
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int read = channel.read( readBuffer );
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if ( read <= 0 )
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{
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modified = true;
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channel.position( channel.position() - readBuffer.position() );
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channel.write( writeBuffer );
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return;
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}
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len -= read;
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}
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( ( Buffer ) readBuffer ).flip();
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if ( readBuffer.compareTo( writeBuffer ) != 0 )
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{
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modified = true;
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channel.position( channel.position() - readBuffer.remaining() );
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channel.write( writeBuffer );
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}
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}
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}
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@Override
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public void close() throws IOException
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{
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flush();
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long position = channel.position();
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if ( position != channel.size() )
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{
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if ( !modified )
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{
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FileTime now = FileTime.from( Instant.now() );
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Files.setLastModifiedTime( path, now );
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modified = true;
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}
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channel.truncate( position );
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}
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channel.close();
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}
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public boolean isModified()
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{
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return modified;
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}
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}

‎src/main/java/org/codehaus/plexus/util/io/CachingWriter.java

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package org.codehaus.plexus.util.io;
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/*
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* Copyright The Codehaus Foundation.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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import java.io.File;
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import java.io.IOException;
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import java.io.OutputStreamWriter;
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import java.io.StringWriter;
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import java.nio.charset.Charset;
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import java.nio.file.Files;
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import java.nio.file.Path;
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import java.util.Arrays;
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import java.util.Objects;
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/**
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* Caching Writer to avoid overwriting a file with
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* the same content.
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*/
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public class CachingWriter extends OutputStreamWriter
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{
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private final CachingOutputStream cos;
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public CachingWriter( File path, Charset charset ) throws IOException
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{
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this( Objects.requireNonNull( path ).toPath(), charset );
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}
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public CachingWriter( Path path, Charset charset ) throws IOException
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{
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this( path, charset, 32 * 1024 );
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}
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public CachingWriter( Path path, Charset charset, int bufferSize ) throws IOException
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{
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this( new CachingOutputStream( path, bufferSize ), charset );
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}
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private CachingWriter( CachingOutputStream outputStream, Charset charset ) throws IOException
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{
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super( outputStream, charset );
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this.cos = outputStream;
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}
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public boolean isModified()
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{
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return cos.isModified();
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}
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}

‎src/test/java/org/codehaus/plexus/util/io/CachingOutputStreamTest.java

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package org.codehaus.plexus.util.io;
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/*
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* Copyright The Codehaus Foundation.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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import java.io.IOException;
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import java.io.OutputStream;
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import java.nio.charset.StandardCharsets;
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import java.nio.file.Files;
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import java.nio.file.Path;
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import java.nio.file.Paths;
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import java.nio.file.attribute.FileTime;
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import java.util.Objects;
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import org.junit.Before;
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import org.junit.Test;
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import static org.junit.Assert.assertArrayEquals;
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import static org.junit.Assert.assertEquals;
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import static org.junit.Assert.assertFalse;
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import static org.junit.Assert.assertNotEquals;
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import static org.junit.Assert.assertTrue;
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public class CachingOutputStreamTest
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{
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Path tempDir;
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Path checkLastModified;
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FileTime lm;
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@Before
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public void setup() throws IOException
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{
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Path dir = Paths.get( "target/io" );
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Files.createDirectories( dir );
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tempDir = Files.createTempDirectory( dir, "temp-" );
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checkLastModified = tempDir.resolve( ".check" );
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Files.newOutputStream( checkLastModified ).close();
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lm = Files.getLastModifiedTime( checkLastModified );
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}
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private void waitLastModified() throws IOException, InterruptedException
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{
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while ( true )
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{
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Files.newOutputStream( checkLastModified ).close();
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FileTime nlm = Files.getLastModifiedTime( checkLastModified );
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if ( !Objects.equals( nlm, lm ) )
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{
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lm = nlm;
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break;
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}
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Thread.sleep( 10 );
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}
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}
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@Test
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public void testWriteNoExistingFile() throws IOException, InterruptedException
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{
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byte[] data = "Hello world!".getBytes( StandardCharsets.UTF_8 );
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Path path = tempDir.resolve( "file.txt" );
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assertFalse( Files.exists( path ) );
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try ( CachingOutputStream cos = new CachingOutputStream( path, 4 ) )
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{
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cos.write( data );
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}
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assertTrue( Files.exists( path ) );
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byte[] read = Files.readAllBytes( path );
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assertArrayEquals( data, read );
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FileTime modified = Files.getLastModifiedTime( path );
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waitLastModified();
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try ( CachingOutputStream cos = new CachingOutputStream( path, 4 ) )
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{
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cos.write( data );
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}
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assertTrue( Files.exists( path ) );
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read = Files.readAllBytes( path );
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assertArrayEquals( data, read );
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FileTime newModified = Files.getLastModifiedTime( path );
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assertEquals( modified, newModified );
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modified = newModified;
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waitLastModified();
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// write longer data
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data = "Good morning!".getBytes( StandardCharsets.UTF_8 );
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try ( CachingOutputStream cos = new CachingOutputStream( path, 4 ) )
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{
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cos.write( data );
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}
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assertTrue( Files.exists( path ) );
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read = Files.readAllBytes( path );
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assertArrayEquals( data, read );
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newModified = Files.getLastModifiedTime( path );
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assertNotEquals( modified, newModified );
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modified = newModified;
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waitLastModified();
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// different data same size
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data = "Good mornong!".getBytes( StandardCharsets.UTF_8 );
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try ( CachingOutputStream cos = new CachingOutputStream( path, 4 ) )
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{
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cos.write( data );
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}
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assertTrue( Files.exists( path ) );
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read = Files.readAllBytes( path );
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assertArrayEquals( data, read );
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newModified = Files.getLastModifiedTime( path );
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assertNotEquals( modified, newModified );
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modified = newModified;
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waitLastModified();
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// same data but shorter
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data = "Good mornon".getBytes( StandardCharsets.UTF_8 );
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try ( CachingOutputStream cos = new CachingOutputStream( path, 4 ) )
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{
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cos.write( data );
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}
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assertTrue( Files.exists( path ) );
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read = Files.readAllBytes( path );
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assertArrayEquals( data, read );
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newModified = Files.getLastModifiedTime( path );
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assertNotEquals( modified, newModified );
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modified = newModified;
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}
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}

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