org.csstudio.archive.engine.server.json.JSONStructure.java Source code

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Here is the source code for org.csstudio.archive.engine.server.json.JSONStructure.java

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/*******************************************************************************
 * Copyright (c) 2017 Science & Technology Facilities Council.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 ******************************************************************************/
package org.csstudio.archive.engine.server.json;

import java.io.PrintWriter;
import java.io.StringWriter;

import org.apache.commons.lang3.StringEscapeUtils;

/** Represents a generic JSON structure i.e. a list or an object
 *  @author Dominic Oram
 */

public abstract class JSONStructure {
    /** Writer */
    private PrintWriter buf;
    final private StringWriter out = new StringWriter();

    protected boolean isFirstItem = true;
    protected boolean isClosed = false;

    /**
     * Creates a structure that ouputs the JSON to a StringWriter.
     */
    public JSONStructure() {
        this.buf = new PrintWriter(out);
        open();
    }

    /** Creates an object that writes to a provided PrintWriter.
     *  This is currently only used for the root object.
     *
     * @param buf The PrintWriter to write to.
     */
    protected JSONStructure(final PrintWriter buf) {
        this.buf = buf;
        open();
    }

    /**
     * Formats a string for JSON.
     * @param str The string to format.
     * @return A correctly formatted string.
     */
    protected String formatString(final String str) {
        return "\"" + StringEscapeUtils.escapeJava(str) + "\"";
    }

    /**
     * Add a list seperator to the JSON object if this is not the first item.
     */
    public void listSeperator() {
        if (!isFirstItem) {
            buf.print(",");
        } else {
            isFirstItem = false;
        }
    }

    protected void throwIfClosed() {
        if (isClosed) {
            throw new IllegalStateException("The JSON structure is already closed and cannot be written to");
        }
    }

    protected abstract void open();

    /**
     * Closes the JSON structure
     */
    public void close() {
        throwIfClosed();
        printCloseChar();
        isClosed = true;
    }

    protected abstract void printCloseChar();

    /**
     * Checks that printing is possible and prints to the buffer.
     * @param toPrint The text to print.
     */
    protected void print(String toPrint) {
        throwIfClosed();
        buf.print(toPrint);
    }

    @Override
    public String toString() {
        return out.toString();
    }
}