org.mybatis.scripting.velocity.VelocityFacade Maven / Gradle / Ivy

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/*
 *    Copyright 2012-2022 the original author or authors.
 *
 *    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
 *
 *       https://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.mybatis.scripting.velocity;

import java.io.StringReader;
import java.io.StringWriter;
import java.util.HashMap;
import java.util.Map;
import java.util.Properties;
import java.util.stream.Collectors;

import org.apache.ibatis.builder.BuilderException;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.scripting.ScriptingException;
import org.apache.velocity.Template;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.runtime.RuntimeConstants;
import org.apache.velocity.runtime.RuntimeInstance;
import org.apache.velocity.runtime.parser.node.SimpleNode;

public class VelocityFacade {

  private static final RuntimeInstance engine = new RuntimeInstance();
  private static final Map additionalCtxAttributes = new HashMap<>();

  private VelocityFacade() {
    // Prevent instantiation
  }

  /**
   * Initialize a template engine.
   *
   * @param driverConfig
   *          a language driver configuration
   *
   * @since 2.1.0
   */
  public static void initialize(VelocityLanguageDriverConfig driverConfig) {
    Properties properties = new Properties();
    driverConfig.getVelocitySettings().forEach(properties::setProperty);
    properties.setProperty(RuntimeConstants.CUSTOM_DIRECTIVES, driverConfig.generateCustomDirectivesString());
    engine.init(properties);
    additionalCtxAttributes.putAll(driverConfig.getAdditionalContextAttributes().entrySet().stream()
        .collect(Collectors.toMap(Map.Entry::getKey, v -> {
          try {
            return Resources.classForName(v.getValue()).getConstructor().newInstance();
          } catch (Exception e) {
            throw new ScriptingException("Cannot load additional context attribute class.", e);
          }
        })));
  }

  /**
   * Destroy a template engine.
   *
   * @since 2.1.0
   */
  public static void destroy() {
    engine.reset();
    additionalCtxAttributes.clear();
  }

  public static Object compile(String script, String name) {
    try {
      StringReader reader = new StringReader(script);
      Template template = new Template();
      SimpleNode node = engine.parse(reader, template);
      template.setRuntimeServices(engine);
      template.setData(node);
      template.setName(name);
      template.initDocument();
      return template;
    } catch (Exception ex) {
      throw new BuilderException("Error parsing velocity script '" + name + "'", ex);
    }
  }

  public static String apply(Object template, Map context) {
    final StringWriter out = new StringWriter();
    context.putAll(additionalCtxAttributes);
    ((Template) template).merge(new VelocityContext(context), out);
    return out.toString();
  }

}