freemarker.cache.MultiTemplateLoader Maven / Gradle / Ivy
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/*
* 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.
*/
package freemarker.cache;
import java.io.IOException;
import java.io.Reader;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import freemarker.template.utility.NullArgumentException;
/**
* A {@link TemplateLoader} that uses a set of other loaders to load the templates. On every request, loaders are
* queried in the order of their appearance in the array of loaders provided to the constructor. However, by default, if
* a request for some template name was already satisfied in the past by one of the loaders, that loader is queried
* first (stickiness). This behavior can be disabled with {@link #setSticky(boolean)}, then the loaders are always
* queried in the order of their appearance in the array.
*
* This class is thread-safe.
*/
public class MultiTemplateLoader implements StatefulTemplateLoader {
private final TemplateLoader[] templateLoaders;
private final Map lastTemplateLoaderForName
= new ConcurrentHashMap<>();
private boolean sticky = true;
/**
* Creates a new instance that will use the specified template loaders.
*
* @param templateLoaders
* the template loaders that are used to load templates, in the order as they will be searched
* (except where {@linkplain #setSticky(boolean) stickiness} says otherwise).
*/
public MultiTemplateLoader(TemplateLoader[] templateLoaders) {
NullArgumentException.check("templateLoaders", templateLoaders);
this.templateLoaders = templateLoaders.clone();
}
@Override
public Object findTemplateSource(String name)
throws IOException {
TemplateLoader lastTemplateLoader = null;
if (sticky) {
// Use soft affinity - give the loader that last found this
// resource a chance to find it again first.
lastTemplateLoader = lastTemplateLoaderForName.get(name);
if (lastTemplateLoader != null) {
Object source = lastTemplateLoader.findTemplateSource(name);
if (source != null) {
return new MultiSource(source, lastTemplateLoader);
}
}
}
// If there is no affine loader, or it could not find the resource
// again, try all loaders in order of appearance. If any manages
// to find the resource, then associate it as the new affine loader
// for this resource.
for (TemplateLoader templateLoader : templateLoaders) {
if (lastTemplateLoader != templateLoader) {
Object source = templateLoader.findTemplateSource(name);
if (source != null) {
if (sticky) {
lastTemplateLoaderForName.put(name, templateLoader);
}
return new MultiSource(source, templateLoader);
}
}
}
if (sticky) {
lastTemplateLoaderForName.remove(name);
}
// Resource not found
return null;
}
@Override
public long getLastModified(Object templateSource) {
return ((MultiSource) templateSource).getLastModified();
}
@Override
public Reader getReader(Object templateSource, String encoding)
throws IOException {
return ((MultiSource) templateSource).getReader(encoding);
}
@Override
public void closeTemplateSource(Object templateSource)
throws IOException {
((MultiSource) templateSource).close();
}
/**
* Clears the sickiness memory, also resets the state of all enclosed {@link StatefulTemplateLoader}-s.
*/
@Override
public void resetState() {
lastTemplateLoaderForName.clear();
for (TemplateLoader loader : templateLoaders) {
if (loader instanceof StatefulTemplateLoader) {
((StatefulTemplateLoader) loader).resetState();
}
}
}
/**
* Represents a template source bound to a specific template loader. It serves as the complete template source
* descriptor used by the MultiTemplateLoader class.
*/
static final class MultiSource {
private final Object source;
private final TemplateLoader loader;
MultiSource(Object source, TemplateLoader loader) {
this.source = source;
this.loader = loader;
}
long getLastModified() {
return loader.getLastModified(source);
}
Reader getReader(String encoding)
throws IOException {
return loader.getReader(source, encoding);
}
void close()
throws IOException {
loader.closeTemplateSource(source);
}
Object getWrappedSource() {
return source;
}
@Override
public boolean equals(Object o) {
if (o instanceof MultiSource) {
MultiSource m = (MultiSource) o;
return m.loader.equals(loader) && m.source.equals(source);
}
return false;
}
@Override
public int hashCode() {
return loader.hashCode() + 31 * source.hashCode();
}
@Override
public String toString() {
return source.toString();
}
}
/**
* Show class name and some details that are useful in template-not-found errors.
*
* @since 2.3.21
*/
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append("MultiTemplateLoader(");
for (int i = 0; i < templateLoaders.length; i++) {
if (i != 0) {
sb.append(", ");
}
sb.append("loader").append(i + 1).append(" = ").append(templateLoaders[i]);
}
sb.append(")");
return sb.toString();
}
/**
* Returns the number of {@link TemplateLoader}-s directly inside this {@link TemplateLoader}.
*
* @since 2.3.23
*/
public int getTemplateLoaderCount() {
return templateLoaders.length;
}
/**
* Returns the {@link TemplateLoader} at the given index.
*
* @param index
* Must be below {@link #getTemplateLoaderCount()}.
*/
public TemplateLoader getTemplateLoader(int index) {
return templateLoaders[index];
}
/**
* Getter pair of {@link #setSticky(boolean)}.
*
* @since 2.3.24
*/
public boolean isSticky() {
return sticky;
}
/**
* Sets if for a name that was already loaded earlier the same {@link TemplateLoader} will be tried first, or
* we always try the {@link TemplateLoader}-s strictly in the order as it was specified in the constructor.
* The default is {@code true}.
*
* @since 2.3.24
*/
public void setSticky(boolean sticky) {
this.sticky = sticky;
}
}