edu.cornell.mannlib.vitro.webapp.controller.json.JsonObjectProducer.java Source code

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Here is the source code for edu.cornell.mannlib.vitro.webapp.controller.json.JsonObjectProducer.java

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/* $This file is distributed under the terms of the license in /doc/license.txt$ */

package edu.cornell.mannlib.vitro.webapp.controller.json;

import java.io.IOException;
import java.io.Writer;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.json.JSONException;
import org.json.JSONObject;

import edu.cornell.mannlib.vitro.webapp.controller.VitroRequest;

/**
 * A base for classes that produce a JSON object, based on the parameters in the
 * request.
 * 
 * The result is never empty. At worst, it is an object that contains only an
 * "errorMessage" field.
 * 
 * If an exception occurrs during processing, The "errorMessage" field will
 * contain the exception message and the response status will be set to 500
 * (server error). Normally, "errorMessage" will be empty, and the status will
 * default to 200 (OK).
 */
public abstract class JsonObjectProducer extends JsonProducer {
    private static final Log log = LogFactory.getLog(JsonObjectProducer.class);

    protected final VitroRequest vreq;
    protected final ServletContext ctx;

    protected JsonObjectProducer(VitroRequest vreq) {
        this.vreq = vreq;
        this.ctx = vreq.getSession().getServletContext();
    }

    /**
     * Sub-classes implement this method. Given the request, produce a JSON
     * object as the result.
     */
    protected abstract JSONObject process() throws Exception;

    public final void process(HttpServletResponse resp) throws IOException {
        JSONObject jsonObject = null;
        String errorMessage = "";

        try {
            jsonObject = process();
        } catch (Exception e) {
            log.error("Failed to create JSON response", e);
            errorMessage = e.toString();
            resp.setStatus(500 /* HttpURLConnection.HTTP_SERVER_ERROR */);
        }

        if (jsonObject == null) {
            jsonObject = new JSONObject();
        }

        log.debug("Response to JSON request: " + jsonObject.toString());

        try {
            resp.setCharacterEncoding("UTF-8");
            resp.setContentType("application/json;charset=UTF-8");
            Writer writer = resp.getWriter();

            jsonObject.put("errorMessage", errorMessage);
            writer.write(jsonObject.toString());
        } catch (JSONException e) {
            log.error(e, e);
        }
    }
}