Java tutorial
/** * Licensed to Elasticsearch under one or more contributor * license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright * ownership. Elasticsearch 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 org.elasticsearch.script.mustache; import java.io.StringReader; import java.io.StringWriter; import java.util.Map; import org.elasticsearch.common.Nullable; import org.elasticsearch.common.component.AbstractComponent; import org.elasticsearch.common.inject.Inject; import org.elasticsearch.common.settings.Settings; import org.elasticsearch.script.ExecutableScript; import org.elasticsearch.script.ScriptEngineService; import org.elasticsearch.script.SearchScript; import org.elasticsearch.search.lookup.SearchLookup; import com.fasterxml.jackson.core.io.SegmentedStringWriter; import com.fasterxml.jackson.core.util.BufferRecycler; import com.github.mustachejava.DefaultMustacheFactory; import com.github.mustachejava.Mustache; import com.github.mustachejava.MustacheFactory; /** * Main entry point handling template registration, compilation and * execution. * * Template handling is based on Mustache. Template handling is a two step * process: First compile the string representing the template, the resulting * {@link Mustache} object can then be re-used for subsequent executions. */ public class MustacheScriptEngineService extends AbstractComponent implements ScriptEngineService { /** Factory to generate Mustache objects from. */ private static final MustacheFactory MFACTORY = new DefaultMustacheFactory(); /** * @param settings automatically wired by Guice. * */ @Inject public MustacheScriptEngineService(Settings settings) { super(settings); } /** * Compile a template string to (in this case) a Mustache object than can * later be re-used for execution to fill in missing parameter values. * * @param template * a string representing the template to compile. * @return a compiled template object for later execution. * */ public Object compile(String template) { return MFACTORY.compile(new StringReader(template), "query-template"); } /** * Execute a compiled template object (as retrieved from the compile method) * and fill potential place holders with the variables given. * * @param template * compiled template object. * @param vars * map of variables to use during substitution. * * @return the processed string with all given variables substitued. * */ public Object execute(Object template, Map<String, Object> vars) { SegmentedStringWriter result = new SegmentedStringWriter(new BufferRecycler()); ((Mustache) template).execute(result, vars); return result.getAndClear(); } @Override public String[] types() { return new String[] { "mustache" }; } @Override public String[] extensions() { return new String[] { "mustache" }; } @Override public ExecutableScript executable(Object mustache, @Nullable Map<String, Object> vars) { return new MustacheExecutableScript((Mustache) mustache, vars); } @Override public SearchScript search(Object compiledScript, SearchLookup lookup, @Nullable Map<String, Object> vars) { throw new UnsupportedOperationException(); } @Override public Object unwrap(Object value) { return value; } @Override public void close() { // Nothing to do here } /** * Used at query execution time by script service in order to execute a query template. * */ private class MustacheExecutableScript implements ExecutableScript { /** Compiled template object. */ private Mustache mustache; /** Parameters to fill above object with. */ private Map<String, Object> vars; /** * @param mustache the compiled template object * @param vars the parameters to fill above object with **/ public MustacheExecutableScript(Mustache mustache, Map<String, Object> vars) { this.mustache = mustache; this.vars = vars; } @Override public void setNextVar(String name, Object value) { this.vars.put(name, value); } @Override public Object run() { StringWriter result = new StringWriter(); ((Mustache) mustache).execute(result, vars); return result.toString(); } @Override public Object unwrap(Object value) { return value; } } }