org.apache.lucene.codecs.DocValuesFormat Maven / Gradle / Ivy
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package org.apache.lucene.codecs;
/*
* 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.
*/
import java.io.IOException;
import java.util.ServiceLoader;
import java.util.Set;
import org.apache.lucene.index.SegmentReadState;
import org.apache.lucene.index.SegmentWriteState;
import org.apache.lucene.util.NamedSPILoader;
/**
* Encodes/decodes per-document values.
*
* Note, when extending this class, the name ({@link #getName}) may
* written into the index in certain configurations. In order for the segment
* to be read, the name must resolve to your implementation via {@link #forName(String)}.
* This method uses Java's
* {@link ServiceLoader Service Provider Interface} (SPI) to resolve format names.
*
* If you implement your own format, make sure that it has a no-arg constructor
* so SPI can load it.
* @see ServiceLoader
* @lucene.experimental */
public abstract class DocValuesFormat implements NamedSPILoader.NamedSPI {
private static final NamedSPILoader loader =
new NamedSPILoader<>(DocValuesFormat.class);
/** Unique name that's used to retrieve this format when
* reading the index.
*/
private final String name;
/**
* Creates a new docvalues format.
*
* The provided name will be written into the index segment in some configurations
* (such as when using {@code PerFieldDocValuesFormat}): in such configurations,
* for the segment to be read this class should be registered with Java's
* SPI mechanism (registered in META-INF/ of your jar file, etc).
* @param name must be all ascii alphanumeric, and less than 128 characters in length.
*/
protected DocValuesFormat(String name) {
NamedSPILoader.checkServiceName(name);
this.name = name;
}
/** Returns a {@link DocValuesConsumer} to write docvalues to the
* index. */
public abstract DocValuesConsumer fieldsConsumer(SegmentWriteState state) throws IOException;
/**
* Returns a {@link DocValuesProducer} to read docvalues from the index.
*
* NOTE: by the time this call returns, it must hold open any files it will
* need to use; else, those files may be deleted. Additionally, required files
* may be deleted during the execution of this call before there is a chance
* to open them. Under these circumstances an IOException should be thrown by
* the implementation. IOExceptions are expected and will automatically cause
* a retry of the segment opening logic with the newly revised segments.
*/
public abstract DocValuesProducer fieldsProducer(SegmentReadState state) throws IOException;
@Override
public final String getName() {
return name;
}
@Override
public String toString() {
return "DocValuesFormat(name=" + name + ")";
}
/** looks up a format by name */
public static DocValuesFormat forName(String name) {
if (loader == null) {
throw new IllegalStateException("You called DocValuesFormat.forName() before all formats could be initialized. "+
"This likely happens if you call it from a DocValuesFormat's ctor.");
}
return loader.lookup(name);
}
/** returns a list of all available format names */
public static Set availableDocValuesFormats() {
if (loader == null) {
throw new IllegalStateException("You called DocValuesFormat.availableDocValuesFormats() before all formats could be initialized. "+
"This likely happens if you call it from a DocValuesFormat's ctor.");
}
return loader.availableServices();
}
/**
* Reloads the DocValues format list from the given {@link ClassLoader}.
* Changes to the docvalues formats are visible after the method ends, all
* iterators ({@link #availableDocValuesFormats()},...) stay consistent.
*
* NOTE: Only new docvalues formats are added, existing ones are
* never removed or replaced.
*
*
This method is expensive and should only be called for discovery
* of new docvalues formats on the given classpath/classloader!
*/
public static void reloadDocValuesFormats(ClassLoader classloader) {
loader.reload(classloader);
}
}