net.jpountz.lz4.LZ4Factory Maven / Gradle / Ivy
Show all versions of lz4 Show documentation
package net.jpountz.lz4;
/*
* 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.
*/
import java.lang.reflect.Field;
import java.util.Arrays;
import net.jpountz.util.Native;
/**
* Entry point for the LZ4 API.
*
* This class has 3 instances
* - a {@link #nativeInstance() native} instance which is a JNI binding to
* the original LZ4 C implementation.
*
- a {@link #safeInstance() safe Java} instance which is a pure Java port
* of the original C library,
* - an {@link #unsafeInstance() unsafe Java} instance which is a Java port
* using the unofficial {@link sun.misc.Unsafe} API.
*
*
* Only the {@link #safeInstance() safe instance} is guaranteed to work on your
* JVM, as a consequence it is advised to use the {@link #fastestInstance()} or
* {@link #fastestJavaInstance()} to pull a {@link LZ4Factory} instance.
*
* All methods from this class are very costly, so you should get an instance
* once, and then reuse it whenever possible. This is typically done by storing
* a {@link LZ4Factory} instance in a static field.
*/
public final class LZ4Factory {
private static LZ4Factory instance(String impl) {
try {
return new LZ4Factory(impl);
} catch (Exception e) {
throw new AssertionError(e);
}
}
private static LZ4Factory NATIVE_INSTANCE,
JAVA_UNSAFE_INSTANCE,
JAVA_SAFE_INSTANCE;
/**
* Return a {@link LZ4Factory} instance that returns compressors and
* decompressors that are native bindings to the original C library.
*
* Please note that this instance has some traps you should be aware of:
* - Upon loading this instance, files will be written to the temporary
* directory of the system. Although these files are supposed to be deleted
* when the JVM exits, they might remain on systems that don't support
* removal of files being used such as Windows.
*
- The instance can only be loaded once per JVM. This can be a problem
* if your application uses multiple class loaders (such as most servlet
* containers): this instance will only be available to the children of the
* class loader which has loaded it. As a consequence, it is advised to
* either not use this instance in webapps or to put this library in the lib
* directory of your servlet container so that it is loaded by the system
* class loader.
*
*/
public static synchronized LZ4Factory nativeInstance() {
if (NATIVE_INSTANCE == null) {
NATIVE_INSTANCE = instance("JNI");
}
return NATIVE_INSTANCE;
}
/** Return a {@link LZ4Factory} instance that returns compressors and
* decompressors that are written with Java's official API. */
public static synchronized LZ4Factory safeInstance() {
if (JAVA_SAFE_INSTANCE == null) {
JAVA_SAFE_INSTANCE = instance("JavaSafe");
}
return JAVA_SAFE_INSTANCE;
}
/** Return a {@link LZ4Factory} instance that returns compressors and
* decompressors that may use {@link sun.misc.Unsafe} to speed up compression
* and decompression. */
public static synchronized LZ4Factory unsafeInstance() {
if (JAVA_UNSAFE_INSTANCE == null) {
JAVA_UNSAFE_INSTANCE = instance("JavaUnsafe");
}
return JAVA_UNSAFE_INSTANCE;
}
/**
* Return the fastest available {@link LZ4Factory} instance which does not
* rely on JNI bindings. It first tries to load the
* {@link #unsafeInstance() unsafe instance}, and then the
* {@link #safeInstance() safe Java instance} if the JVM doesn't have a
* working {@link sun.misc.Unsafe}.
*/
public static LZ4Factory fastestJavaInstance() {
try {
return unsafeInstance();
} catch (Throwable t) {
return safeInstance();
}
}
/**
* Return the fastest available {@link LZ4Factory} instance. If the class
* loader is the system class loader and if the
* {@link #nativeInstance() native instance} loads successfully, then the
* {@link #nativeInstance() native instance} is returned, otherwise the
* {@link #fastestJavaInstance() fastest Java instance} is returned.
*
* Please read {@link #nativeInstance() javadocs of nativeInstance()} before
* using this method.
*/
public static LZ4Factory fastestInstance() {
if (Native.isLoaded()
|| Native.class.getClassLoader() == ClassLoader.getSystemClassLoader()) {
try {
return nativeInstance();
} catch (Throwable t) {
return fastestJavaInstance();
}
} else {
return fastestJavaInstance();
}
}
@SuppressWarnings("unchecked")
private static T classInstance(String cls) throws NoSuchFieldException, SecurityException, ClassNotFoundException, IllegalArgumentException, IllegalAccessException {
final Class c = Class.forName(cls);
Field f = c.getField("INSTANCE");
return (T) f.get(null);
}
private final String impl;
private final LZ4Compressor fastCompressor;
private final LZ4Compressor highCompressor;
private final LZ4FastDecompressor fastDecompressor;
private final LZ4SafeDecompressor safeDecompressor;
private LZ4Factory(String impl) throws ClassNotFoundException, NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException {
this.impl = impl;
fastCompressor = classInstance("net.jpountz.lz4.LZ4" + impl + "Compressor");
highCompressor = classInstance("net.jpountz.lz4.LZ4HC" + impl + "Compressor");
fastDecompressor = classInstance("net.jpountz.lz4.LZ4" + impl + "FastDecompressor");
safeDecompressor = classInstance("net.jpountz.lz4.LZ4" + impl + "SafeDecompressor");
// quickly test that everything works as expected
final byte[] original = new byte[] {'a','b','c','d',' ',' ',' ',' ',' ',' ','a','b','c','d','e','f','g','h','i','j'};
for (LZ4Compressor compressor : Arrays.asList(fastCompressor, highCompressor)) {
final int maxCompressedLength = compressor.maxCompressedLength(original.length);
final byte[] compressed = new byte[maxCompressedLength];
final int compressedLength = compressor.compress(original, 0, original.length, compressed, 0, maxCompressedLength);
final byte[] restored = new byte[original.length];
fastDecompressor.decompress(compressed, 0, restored, 0, original.length);
if (!Arrays.equals(original, restored)) {
throw new AssertionError();
}
Arrays.fill(restored, (byte) 0);
final int decompressedLength = safeDecompressor.decompress(compressed, 0, compressedLength, restored, 0);
if (decompressedLength != original.length || !Arrays.equals(original, restored)) {
throw new AssertionError();
}
}
}
/** Return a blazing fast {@link LZ4Compressor}. */
public LZ4Compressor fastCompressor() {
return fastCompressor;
}
/** Return a {@link LZ4Compressor} which requires more memory than
* {@link #fastCompressor()} and is slower but compresses more efficiently. */
public LZ4Compressor highCompressor() {
return highCompressor;
}
/** Return a {@link LZ4FastDecompressor} instance. */
public LZ4FastDecompressor fastDecompressor() {
return fastDecompressor;
}
/** Return a {@link LZ4SafeDecompressor} instance. */
public LZ4SafeDecompressor safeDecompressor() {
return safeDecompressor;
}
/** Return a {@link LZ4UnknownSizeDecompressor} instance.
* @deprecated use {@link #safeDecompressor()} */
public LZ4UnknownSizeDecompressor unknwonSizeDecompressor() {
return safeDecompressor();
}
/** Return a {@link LZ4Decompressor} instance.
* @deprecated use {@link #fastDecompressor()} */
public LZ4Decompressor decompressor() {
return fastDecompressor();
}
/** Prints the fastest instance. */
public static void main(String[] args) {
System.out.println("Fastest instance is " + fastestInstance());
System.out.println("Fastest Java instance is " + fastestJavaInstance());
}
@Override
public String toString() {
return getClass().getSimpleName() + ":" + impl;
}
}