com.nimbusds.common.appendable.JSONArrayWriter Maven / Gradle / Ivy

Go to download
package com.nimbusds.common.appendable;


import java.io.IOException;
import java.io.Writer;
import java.util.HashSet;
import java.util.Set;

import javax.ws.rs.WebApplicationException;

import net.minidev.json.JSONAware;


/**
 * JSON array writer for JAX-RS result streaming.
 */
public class JSONArrayWriter implements Appendable {


	/**
	 * Writer for the appended elements.
	 */
	private final Writer writer;


	/**
	 * No duplicates switch.
	 */
	private final boolean noDuplicates;


	/**
	 * Keeps track of the written elements if {@link #noDuplicates} is
	 * {@code true}.
	 */
	private final Set writtenItems;


	/**
	 * The position of the appender.
	 */
	private boolean first;


	/**
	 * Creates a new JSON array writer. The output JSON array may contain
	 * duplicates.
	 *
	 * @param writer Writer for the JSON array. Must not be {@code null}.
	 */
	public JSONArrayWriter(final Writer writer) {

		this(writer, false);
	}


	/**
	 * Creates a new JSON array writer.
	 *
	 * @param writer       Writer for the JSON array. Must not be
	 *                     {@code null}.
	 * @param noDuplicates {@code true} to ensure no duplicates are written
	 *                     to the JSON array.
	 */
	public JSONArrayWriter(final Writer writer,
			final boolean noDuplicates) {

		if (writer == null) {
			throw new IllegalArgumentException("The writer must not be null");
		}

		this.writer = writer;

		this.noDuplicates = noDuplicates;

		if (noDuplicates) {
			writtenItems = new HashSet<>();
		} else {
			writtenItems = null;
		}

		first = true;
	}


	/**
	 * Writes out the opening '[' of the JSON array.
	 */
	public void writeStart() {

		try {
			writer.write('[');

		} catch (IOException e) {

			throw new WebApplicationException("Couldn't write JSON array: " + e.getMessage(), e);
		}
	}


	@Override
	public void append(final T element) {

		if (element == null) {
			return; // Nothing to append
		}

		if (noDuplicates) {
			if (writtenItems.contains(element)) {
				return; // item already written out
			} else {
				writtenItems.add(element);
			}
		}

		StringBuilder sb = new StringBuilder();

		if (first) {
			first = false;
		} else {
			sb.append(',');
		}

		sb.append(element.toJSONString());

		try {
			writer.write(sb.toString());
			writer.flush();

		} catch (IOException e) {

			throw new WebApplicationException("Couldn't write JSON array: " + e.getMessage(), e);
		}
	}


	/**
	 * Writes out the closing ']' of the JSON array and closes the writer.
	 */
	public void writeEnd() {

		try {
			writer.write(']');
			writer.close();

		} catch (IOException e) {

			throw new WebApplicationException("Couldn't write JSON array: " + e.getMessage(), e);
		}
	}
}