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BVal - Optional JSON Component
There is a newer version: 1.1.2
/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF 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.apache.bval.json;

import java.io.IOException;
import java.io.StringWriter;
import java.io.Writer;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.bval.model.MetaBean;

import freemarker.template.Configuration;
import freemarker.template.Template;
import freemarker.template.TemplateException;

/**
 * Description: Generate a JSON String for a collection of {@link MetaBean}s.
 * This implementation uses a freemarker template to generate the output.

 *
 * This is an optional module which requires the freemarker dependency
 * and template resourece file "bean-infos-json.ftl" with it.
 */
public class JSONGenerator {
    private final Template template;

    public JSONGenerator() throws IOException {
        this("bean-infos-json.ftl");
    }

    public JSONGenerator(String templateName) throws IOException {
        Configuration freemarker = new Configuration();
        freemarker.setNumberFormat("0.######");  // prevent locale-sensitive number format
        freemarker.setClassForTemplateLoading(getClass(), "");
        template = freemarker.getTemplate(templateName);
    }

    public JSONGenerator(Template template) {
        this.template = template;
    }

    public String toJSON(MetaBean metaBean) throws IOException, TemplateException {
        List metaBeans = new ArrayList(1);
        metaBeans.add(metaBean);
        return toJSON(metaBeans);
    }

    public String toJSON(Collection metaBeans)
            throws IOException, TemplateException {
        final StringWriter out = new StringWriter();
        toJSON(metaBeans, out);
        return out.toString();
    }

    public void toJSON(Collection metaBeans, Writer out)
            throws IOException, TemplateException {
        Map rootMap = new HashMap();
        rootMap.put("metaBeans", metaBeans);
        rootMap.put("generator", this);
        template.process(rootMap, out);
    }
}