com.github.jknack.handlebars.Jackson2Helper.java Source code

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Here is the source code for com.github.jknack.handlebars.Jackson2Helper.java

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/**
 * Copyright (c) 2012-2013 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.StringUtils.isEmpty;
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 com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.SerializableString;
import com.fasterxml.jackson.core.io.CharacterEscapes;
import com.fasterxml.jackson.core.io.SegmentedStringWriter;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectWriter;

/**
 * A Jackson 2.x helper.
 * <p>
 * Basic usage:
 * </p>
 *
 * <pre>
 *  Handlebars hbs = new Handlebars();
 *
 *  hbs.registerHelper("json", Jackson2Helper.INSTANCE);
 *
 *  ...
 *
 *  {{json model}}
 * </pre>
 * <p>
 * If <code>model</code> is null an empty string is returned.
 * </p>
 * <p>
 * You can change this using the <code>default</code> option:
 * </p>
 *
 * <pre>
 *  {{json model default="{}"}}
 * </pre>
 *
 * <p>
 * Using a view class:
 * </p>
 *
 * <pre>
 *  {{json model view="foo.MyView"}}
 * </pre>
 * <p>
 * Using alias for views:
 * </p>
 *
 * <pre>
 *  {{json model view="myView"}}
 * </pre>
 *
 * <p>
 * Escape HTML chars:
 * </p>
 *
 * <pre>
 *  {{json model escapeHtml=true}}
 * </pre>
 *
 * <p>
 * Pretty printer:
 * </p>
 *
 * <pre>
 *  {{json model pretty=true}}
 * </pre>
 *
 * @author edgar.espina
 * @since 0.4.0
 */
public class Jackson2Helper implements Helper<Object> {

    /**
     * Escape HTML chars from JSON content.
     * See http://www.cowtowncoder.com/blog/archives/2012/08/entry_476.html
     *
     * @author edgar.espina
     * @since 1.0.0
     */
    @SuppressWarnings("serial")
    private static class HtmlEscapes extends CharacterEscapes {

        /**
         * The escape table.
         */
        private int[] escapeTable;
        {
            // Start with set of characters known to require escaping (double-quote, backslash etc)
            escapeTable = CharacterEscapes.standardAsciiEscapesForJSON();
            // and force escaping of a few others:
            escapeTable['<'] = CharacterEscapes.ESCAPE_STANDARD;
            escapeTable['>'] = CharacterEscapes.ESCAPE_STANDARD;
            escapeTable['&'] = CharacterEscapes.ESCAPE_STANDARD;
            escapeTable['\''] = CharacterEscapes.ESCAPE_STANDARD;
        }

        @Override
        public int[] getEscapeCodesForAscii() {
            return escapeTable;
        }

        @Override
        public SerializableString getEscapeSequence(final int ch) {
            return null;
        }

    }

    /**
     * A singleton version of {@link Jackson2Helper}.
     */
    public static final Helper<Object> INSTANCE = new Jackson2Helper();

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

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

    /**
     * Creates a new {@link Jackson2Helper}.
     *
     * @param objectMapper The object's mapper. Required.
     */
    public Jackson2Helper(final ObjectMapper objectMapper) {
        mapper = notNull(objectMapper, "The object mapper is required.");
    }

    /**
     * Creates a new {@link Jackson2Helper}.
     */
    private Jackson2Helper() {
        this(new ObjectMapper());
    }

    @Override
    public CharSequence apply(final Object context, final Options options) throws IOException {
        if (context == null) {
            return options.hash("default", "");
        }
        String viewName = options.hash("view", "");
        JsonGenerator generator = null;
        try {
            final ObjectWriter writer;
            // do we need to use a view?
            if (!isEmpty(viewName)) {
                Class<?> viewClass = alias.get(viewName);
                if (viewClass == null) {
                    viewClass = getClass().getClassLoader().loadClass(viewName);
                }
                writer = mapper.writerWithView(viewClass);
            } else {
                writer = mapper.writer();
            }
            JsonFactory jsonFactory = mapper.getFactory();

            SegmentedStringWriter output = new SegmentedStringWriter(jsonFactory._getBufferRecycler());

            // creates a json generator.
            generator = jsonFactory.createJsonGenerator(output);

            Boolean escapeHtml = options.hash("escapeHTML", Boolean.FALSE);
            // do we need to escape html?
            if (escapeHtml) {
                generator.setCharacterEscapes(new HtmlEscapes());
            }

            Boolean pretty = options.hash("pretty", Boolean.FALSE);

            // write the JSON output.
            if (pretty) {
                writer.withDefaultPrettyPrinter().writeValue(generator, context);
            } else {
                writer.writeValue(generator, context);
            }

            generator.close();

            return new Handlebars.SafeString(output.getAndClear());
        } catch (ClassNotFoundException ex) {
            throw new IllegalArgumentException(viewName, ex);
        } finally {
            if (generator != null && !generator.isClosed()) {
                generator.close();
            }
        }
    }

    /**
     * Add an alias for the given view class.
     *
     * @param alias The view alias. Required.
     * @param viewClass The view class. Required.
     * @return This helper.
     */
    public Jackson2Helper 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;
    }
}