/*
* Copyright [2012-2015] PayPal Software Foundation
*
* Licensed 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.
*/
package ml.shifu.guagua.util;
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.Serializable;
import java.util.Iterator;
import ml.shifu.guagua.GuaguaRuntimeException;
/**
* A list wrapper to implement store data into disk.
*
* <p>
* No size limit for this list but user should make sure valid fileName when constructing.
*
* <p>
* Only two stages support in such kind of list. The first one is WRITE, the next is read. So far random WRITE and READ
* are not supported in this list.
*
* <p>
* WARNING: {@link #close()} should be called at last if use such List.
*
* @author Zhang David (pengzhang@paypal.com)
*/
public class DiskList<T extends Serializable> implements AppendList<T> {
/**
* Serializer instance to serialize object to bytes or verse visa.
*/
private ObjectSerializer<T> serializer = new JavaObjectSerializer<T>();
private DataOutputStream outputStream;
private DataInputStream inputStream;
/**
* Internal state for WRITE or READ
*/
private State state = State.WRITE;
/**
* File used to store elements
*/
private File file;
/**
* Number of elements in this list
*/
private long count;
/**
* Constructor with file name in current working dir.
*/
public DiskList(String fileName) {
try {
this.file = new File(fileName);
this.outputStream = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(file)));
this.inputStream = new DataInputStream(new BufferedInputStream(new FileInputStream(file)));
} catch (FileNotFoundException e) {
throw new GuaguaRuntimeException(e);
}
}
/**
* Switch state from WRITE to READ
*/
@Override
public void switchState() {
this.state = State.READ;
}
/**
* Re-open stream for iterators.
*/
public void reOpen() {
close();
try {
this.inputStream = new DataInputStream(new BufferedInputStream(new FileInputStream(file)));
} catch (FileNotFoundException e) {
throw new GuaguaRuntimeException(e);
}
}
@Override
public boolean append(T t) {
if(this.state != State.WRITE) {
throw new IllegalStateException();
}
this.count += 1;
byte[] bytes = getSerializer().serialize(t);
try {
this.outputStream.writeInt(bytes.length);
for(byte b: bytes) {
this.outputStream.writeByte(b);
}
} catch (IOException e) {
throw new GuaguaRuntimeException(e);
}
return true;
}
/**
* This method should be called at the end of {@link DiskList} usage to release file descriptors.
*/
public void close() {
try {
this.outputStream.close();
this.inputStream.close();
} catch (IOException ignore) {
}
}
/*
* (non-Javadoc)
*
* @see java.lang.Iterable#iterator()
*/
@Override
public Iterator<T> iterator() {
if(this.state != State.READ) {
throw new IllegalStateException();
}
return new Iterator<T>() {
@Override
public boolean hasNext() {
try {
return DiskList.this.inputStream.available() > 0;
} catch (IOException e) {
return false;
}
}
@Override
public T next() {
try {
int length = DiskList.this.inputStream.readInt();
byte[] bytes = new byte[length];
for(int i = 0; i < bytes.length; i++) {
bytes[i] = DiskList.this.inputStream.readByte();
}
return DiskList.this.getSerializer().deserialize(bytes, null);
} catch (IOException e) {
throw new GuaguaRuntimeException(e);
}
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
};
}
/**
* @return the serializer
*/
public ObjectSerializer<T> getSerializer() {
return serializer;
}
/**
* @param serializer
* the serializer to set
*/
public void setSerializer(ObjectSerializer<T> serializer) {
this.serializer = serializer;
}
@Override
public int size() {
return (int)this.count;
}
/*
* (non-Javadoc)
*
* @see ml.shifu.guagua.util.AppendList#clear()
*/
@Override
public void clear() {
FileUtils.deleteQuietly(file);
}
}