com.github.jknack.handlebars.JSONHelper.java Source code

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Here is the source code for com.github.jknack.handlebars.JSONHelper.java

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/**
 * Copyright (c) 2012 Edgar Espina
 * This file is part of Handlebars.java.
 * 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.
 */
package com.github.jknack.handlebars;

import static org.apache.commons.lang3.Validate.notEmpty;
import static org.apache.commons.lang3.Validate.notNull;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.ObjectWriter;

/**
 * A Jackson 1.x helper.
 * <p>
 * Basic usage:
 * </p>
 *
 * <pre>
 *  Handlebars hbs = new Handlebars();
 *
 *  hbs.registerHelper("json", JSONHelper.INSTANCE);
 *
 *  ...
 *
 *  {{json model}}
 * </pre>
 * <p>
 * View class usage:
 * </p>
 *
 * <pre>
 *  Handlebars hbs = new Handlebars();
 *
 *  hbs.registerHelper("json", JSONHelper.INSTANCE);
 *
 *  ...
 *
 *  {{json model view="foo.MyView"}}
 *
 * </pre>
 *
 * <p>
 * View alias usage:
 * </p>
 *
 * <pre>
 *
 *  Handlebars hbs = new Handlebars();
 *
 *  hbs.registerHelper("json", JSONHelper.INSTANCE
 *    .viewAlias("myView", foo.MyView.class));
 *
 *  ...
 *
 *  {{json model view="myView"}}
 *
 * </pre>
 *
 * @author edgar.espina
 * @since 0.4.0
 */
public class JSONHelper implements Helper<Object> {

    /**
     * A singleton version of {@link JSONHelper}.
     */
    public static final Helper<Object> INSTANCE = new JSONHelper();

    /**
     * The JSON parser.
     */
    private final ObjectMapper mapper;

    /**
     * Class alias registry.
     */
    private final Map<String, Class<?>> alias = new HashMap<String, Class<?>>();

    /**
     * Creates a new {@link JSONHelper}.
     *
     * @param objectMapper The object's mapper. Required.
     */
    public JSONHelper(final ObjectMapper objectMapper) {
        mapper = notNull(objectMapper, "The object mapper is required.");
    }

    /**
     * Creates a new {@link JSONHelper}.
     */
    private JSONHelper() {
        this(new ObjectMapper());
    }

    @Override
    public CharSequence apply(final Object context, final Options options) throws IOException {
        if (context == null) {
            return "";
        }
        String viewName = options.hash("view", "");
        final ObjectWriter writer;
        if (viewName.length() > 0) {
            try {
                Class<?> viewClass = alias.get(viewName);
                if (viewClass == null) {
                    viewClass = getClass().getClassLoader().loadClass(viewName);
                }
                writer = mapper.writerWithView(viewClass);
            } catch (ClassNotFoundException ex) {
                throw new IllegalArgumentException(viewName, ex);
            }
        } else {
            writer = mapper.writer();
        }
        return new Handlebars.SafeString(writer.writeValueAsString(context));
    }

    /**
     * Add an alias for the given view class.
     *
     * @param alias The view alias. Required.
     * @param viewClass The view class. Required.
     * @return This helper.
     */
    public JSONHelper viewAlias(final String alias, final Class<?> viewClass) {
        this.alias.put(notEmpty(alias, "A view alias is required."),
                notNull(viewClass, "A view class is required."));
        return this;
    }
}