第6章编解码技术

1 Java序列化的缺点

java序列化通过实现Serializable接口来实现

无法跨语言
序列化后的码流太大
序列化性能太低

java序列化的两个目的：网络传输和对象的持久化

对比的是java原生序列化和二进制序列化

java序列化方案：首先把对象信息写到ObjectOutputStream 中，然后再写到ByteArrayOutputStream 中，最后写到字节数组中；

二进制序列化方案：首先把name字段占用的大小写入，然后写入name的值，最后写入id；

用于测试序列化码流大小和序列化性能的对象

public class UserInfo implements Serializable {

	/**
	 * 默认的序列号
	 */
	private static final long serialVersionUID = 1L;

	private String userName;

	private int userID;

	public UserInfo buildUserName(String userName) {
		this.userName = userName;
		return this;
	}

	public UserInfo buildUserID(int userID) {
		this.userID = userID;
		return this;
	}

	/**
	 * @return the userName
	 */
	public final String getUserName() {
		return userName;
	}

	/**
	 * @param userName
	 *            the userName to set
	 */
	public final void setUserName(String userName) {
		this.userName = userName;
	}

	/**
	 * @return the userID
	 */
	public final int getUserID() {
		return userID;
	}

	/**
	 * @param userID
	 *            the userID to set
	 */
	public final void setUserID(int userID) {
		this.userID = userID;
	}

	public byte[] codeC() {
		ByteBuffer buffer = ByteBuffer.allocate(1024);
		byte[] value = this.userName.getBytes();
		buffer.putInt(value.length);
		buffer.put(value);
		buffer.putInt(this.userID);
		buffer.flip();
		value = null;
		byte[] result = new byte[buffer.remaining()];
		buffer.get(result);
		return result;
	}

	public byte[] codeC(ByteBuffer buffer) {
		buffer.clear();
		byte[] value = this.userName.getBytes();
		buffer.putInt(value.length);
		buffer.put(value);
		buffer.putInt(this.userID);
		buffer.flip();
		value = null;
		byte[] result = new byte[buffer.remaining()];
		buffer.get(result);
		return result;
	}
}

测试码流大小：

public class TestUserInfo {

	/**
	 * @param args
	 * @throws IOException
	 */
	public static void main(String[] args) throws IOException {
		UserInfo info = new UserInfo();
		info.buildUserID(100).buildUserName("Welcome to Netty");
		
		ByteArrayOutputStream bos = new ByteArrayOutputStream();
		ObjectOutputStream os = new ObjectOutputStream(bos);
		os.writeObject(info);
		os.flush();
		os.close();
		byte[] b = bos.toByteArray();
		System.out.println("The jdk serializable length is : " + b.length);
		bos.close();
		System.out.println("-------------------------------------");
		System.out.println("The byte array serializable length is : " + info.codeC().length);

	}

}

输出：

The jdk serializable length is : 127
————————————-
The byte array serializable length is : 24

测试序列化性能：

public class PerformTestUserInfo {

	/**
	 * @param args
	 * @throws IOException
	 */
	public static void main(String[] args) throws IOException {
		UserInfo info = new UserInfo();
		info.buildUserID(100).buildUserName("Welcome to Netty");
		int loop = 1000000;
		ByteArrayOutputStream bos = null;
		ObjectOutputStream os = null;
		long startTime = System.currentTimeMillis();
		for (int i = 0; i < loop; i++) {
			bos = new ByteArrayOutputStream();
			os = new ObjectOutputStream(bos);
			os.writeObject(info);
			os.flush();
			os.close();
			byte[] b = bos.toByteArray();
			bos.close();
		}
		long endTime = System.currentTimeMillis();
		System.out.println("The jdk serializable cost time is  : " + (endTime - startTime) + " ms");

		System.out.println("-------------------------------------");

		ByteBuffer buffer = ByteBuffer.allocate(1024);
		startTime = System.currentTimeMillis();
		for (int i = 0; i < loop; i++) {
			byte[] b = info.codeC(buffer);
		}
		endTime = System.currentTimeMillis();
		System.out.println("The byte array serializable cost time is : " + (endTime - startTime) + " ms");

	}

}

输出：

The jdk serializable cost time is : 2029 ms
————————————-
The byte array serializable cost time is : 135 ms