org.culturegraph.mf.stream.converter.SimpleJsonEncoder.java Source code

Introduction

Here is the source code for org.culturegraph.mf.stream.converter.SimpleJsonEncoder.java

Source

/*
 *  Copyright 2013, 2014 Deutsche Nationalbibliothek
 *
 *  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 org.culturegraph.mf.stream.converter;

import java.util.Deque;
import java.util.LinkedList;

import org.apache.commons.lang.StringEscapeUtils;
import org.culturegraph.mf.framework.DefaultStreamPipe;
import org.culturegraph.mf.framework.ObjectReceiver;
import org.culturegraph.mf.framework.StreamReceiver;
import org.culturegraph.mf.framework.annotations.Description;
import org.culturegraph.mf.framework.annotations.In;
import org.culturegraph.mf.framework.annotations.Out;

/**
 * Serialises an object as JSON. Records and entities are represented as objects
 * unless their name ends with []. If the name ends with [], an array is
 * created.
 * 
 * @author Markus Geipel
 * 
 */
@Description("Serialises an object as JSON")
@In(StreamReceiver.class)
@Out(String.class)
public final class SimpleJsonEncoder extends DefaultStreamPipe<ObjectReceiver<String>> {

    public static final String ARRAY_MARKER = "[]";

    private StringBuilder builder = new StringBuilder();
    private final Deque<Character> bracketStack = new LinkedList<Character>();
    private final Deque<Boolean> commaStack = new LinkedList<Boolean>();
    private boolean commaNeeded;

    @Override
    public void startRecord(final String id) {
        builder.append('{');
        bracketStack.push(Character.valueOf('}'));
    }

    @Override
    public void endRecord() {
        builder.append('}');
        bracketStack.clear();
        getReceiver().process(builder.toString());
        builder = new StringBuilder();
        commaStack.clear();
    }

    @Override
    public void startEntity(final String name) {

        if (commaNeeded) {
            builder.append(", ");
        }
        commaNeeded = true;

        if (name.endsWith(ARRAY_MARKER)) {
            builder.append("\"" + escape(name.substring(0, name.length() - ARRAY_MARKER.length())) + "\": [ ");
            bracketStack.push(Character.valueOf(']'));
        } else {
            if (inArray()) {
                builder.append(" { ");
            } else {
                builder.append("\"" + escape(name) + "\": { ");
            }

            bracketStack.push(Character.valueOf('}'));
        }
        commaStack.push(Boolean.valueOf(commaNeeded));
        commaNeeded = false;
    }

    private static String escape(final String string) {
        return StringEscapeUtils.escapeJavaScript(string);
    }

    @Override
    public void endEntity() {
        builder.append(bracketStack.pop() + " ");
        commaNeeded = commaStack.pop().booleanValue();
    }

    @Override
    public void literal(final String name, final String value) {

        if (commaNeeded) {
            builder.append(", ");
        }

        if (inArray()) {
            builder.append("\"" + escape(value) + "\"");
        } else {
            builder.append("\"" + escape(name) + "\":\"" + escape(value) + "\"");
        }

        commaNeeded = true;
    }

    private boolean inArray() {
        return bracketStack.peek().charValue() == ']';
    }

}