XStream笔记「建议收藏」

XStream是一套简洁易用的开源类库，用于将Java对象序列化为XML或者将XML反序列化为Java对象，是Java对象和XML之间一个双向转换器。

1.XStream概述

2.快速入门

User.java:

public class User implements Serializable {
	private static final long serialVersionUID = 1L;
	private int userId;
	private String name;
	public User() {}
	public int getUserId() {
		return userId;
	}
	public void setUserId(int userId) {
		this.userId = userId;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
}

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public class XStreamSample_01 {
	private static XStream xstream;
	static {
		//创建一个XStream实例并指定一个XML解析器
		xstream = new XStream(new DomDriver());
	}
	//初始化转换对象
	public static User getUser() {
		User user = new User();
		user.setUserId(1);
		user.setName("XStreamSample");
		return user;
	}
	//Java对象转化为XML
	public static void objectToXML() throws Exception {
		//1.获得要转化的Java对象实例
		User user = XStreamSample_01.getUser();
		//2.实例化一个文件输出流
		FileOutputStream outputStream = new FileOutputStream("D:\\temporary\\XStream\\user.xml");
		//3.将User对象转换为XML，并保存到指定文件
		xstream.toXML(user, outputStream);
	}
	//XML转化为Java对象
	public static void XMLToObject() throws Exception {
		//实例化一个文件输入流
		FileInputStream inputStream = new FileInputStream("D:\\temporary\\XStream\\user.xml");
		//将XML文件输入流
		User user = (User)xstream.fromXML(inputStream);
		System.out.println("user's id: " + user.getUserId());
		System.out.println("user's name: " + user.getName());
	}
}

3.使用XStream别名：

XStream别名配置包含三种情况：

①.类别名，用alias(String name, Class type)

②.类成员别名，用aliasField(String alias, Class definedIn, String fieldName)

③.类成员作为属性别名，用aliasAttribute(String alias, String attributeName, String alias)单独命名没有意义，还要通过useAttributeFor(Class definedIn, String fieldName)应用到某个类上。

在XStreamSample_01中添加如下代码：

static {
		//设置类别名，默认为当前类名加上包名
		xstream.alias("user", User.class);
		//设置类成员名
		xstream.aliasField("id", User.class, "userId");
		xstream.aliasField("userName", User.class, "name");
	}

XStream转换器：转换一些自定义类型

DateConverter.java

public class DateConverter implements Converter {
	private Locale locale;
	public DateConverter() {
		this.locale = Locale.SIMPLIFIED_CHINESE;
	}
	public DateConverter(Locale locale) {
		super();
		this.locale = locale;
		System.out.println("--有参数的构造方法--");
	}
	//判断要转换的类型
	@Override
	public boolean canConvert(Class arg0) {
		return Date.class.isAssignableFrom(arg0);
	}
	//Java对象到XML转换逻辑
	@Override
	public void marshal(Object arg0, HierarchicalStreamWriter arg1,
			MarshallingContext arg2) {
		//getDateInstance(..):获取给定语言环境的给定格式化风格的日期格式器
		DateFormat formatter = DateFormat.getDateInstance(DateFormat.DATE_FIELD, this.locale);
		arg1.setValue(formatter.format(arg0));
	}
	//XML到Java对象转换
	@Override
	public Object unmarshal(HierarchicalStreamReader arg0,
			UnmarshallingContext arg1) {
		GregorianCalendar calendar = new GregorianCalendar();
		DateFormat formatter = DateFormat.getDateInstance(DateFormat.DATE_FIELD, this.locale);
		try {
			calendar.setTime(formatter.parse(arg0.getValue()));
		} catch (ParseException e) {
			System.out.println(e.getMessage());
		}
		return calendar.getGregorianChange();//获得格里高利历的更改日期
	}

}

调用：

static {
		//创建一个XStream实例并指定一个XML解析器
		xstream = new XStream(new DomDriver());
		xstream.processAnnotations(LoginLog.class);
		//注册自定义的日期转换器
		xstream.registerConverter(new DateConverter(Locale.SIMPLIFIED_CHINESE));
	}

问题：书上没有无参构造方法，但是我不定义无参构造方法会报错。并且如果我不在无参构造方法中初始化locale，在DateFormat formatter = DateFormat.getDateInstance(DateFormat.DATE_FIELD, this.locale);这名会报locale空指针。不知道什么原因。

XStream注解：

示例：

//别名注解，作用于类和字段
@XStreamAlias("loginLog")
public class LoginLog implements Serializable {
	//忽略字段，作用于字段
	@XStreamOmitField
	private static final long serialVersionUID = 1L;
	//转换为属性，作用于字段
	@XStreamAsAttribute
	@XStreamAlias("id")
	private int loginLogId;
	@XStreamAlias("userId")
	private int userId;
	@XStreamAlias("lastIp")
	private String ip;
	@XStreamConverter(DateConverter.class)
	private Date loginDate;
	public LoginLog() {}
	public int getLoginLogId() {
		return loginLogId;
	}
	public void setLoginLogId(int loginLogId) {
		this.loginLogId = loginLogId;
	}
	public int getUserId() {
		return userId;
	}
	public void setUserId(int userId) {
		this.userId = userId;
	}
	public String getIp() {
		return ip;
	}
	public void setIp(String ip) {
		this.ip = ip;
	}
	public Date getLoginDate() {
		return loginDate;
	}
	public void setLoginDate(Date loginDate) {
		this.loginDate = loginDate;
	}
	@Override
	public String toString() {
		return "用户 " +  userId + " 最后一次登陆时间为：" + loginDate;
	}
}

启用XStream提供的注解功能，需要在执行Java对象与XML转换之前，先注册标注了XStream注解的Java对象。

xstream.processAnnotations(LoginLog.class);
		//自动加载注解Bean
		//xstream.autodetectAnnotations(true);

流化对象：

public class ObjectStreamSample {
	private static XStream xstream = new XStream();
	//Java对象转化为XML
	public static LoginLog getLoginLog() {
		LoginLog loginLog = new LoginLog();
		loginLog.setLoginLogId(1);
		loginLog.setUserId(1);
		loginLog.setIp("192.168.1.1");
		loginLog.setLoginDate(new Date());
		return loginLog;
	}
	public void objectToXML() throws Exception {
		LoginLog loginLog = ObjectStreamSample.getLoginLog();
		//创建一个PrintWriter，用于输出
		PrintWriter writer = new PrintWriter("D:\\temporary\\XStream\\loginLog_02.xml");
		//选用一个HierarchicalStreamWriter的实现类来创建输出
		PrettyPrintWriter ppw = new PrettyPrintWriter(writer);
		//CompactWriter cw = new CompactWriter(writer);
		//创建对象输出流
		ObjectOutputStream out = xstream.createObjectOutputStream(ppw);
		out.writeObject(loginLog);
		out.close();
	}
	//XML转化为Java对象
	public LoginLog xmlToObject() throws Exception {
		//通过对象流进行输入操作
		FileReader reader = new FileReader("D:\\temporary\\XStream\\loginLog_02.xml");
		BufferedReader bufferedReader = new BufferedReader(reader);
		//创建对象输入流
		ObjectInputStream input = xstream.createObjectInputStream(bufferedReader);
		//从XML文件中读取对象
		LoginLog loginLog = (LoginLog)input.readObject();
		return loginLog;
	}
}

PrettyPrintWriter和CompactWriter的区别在于，用CompactWriter方法输出的为连续的没有分隔的XML文件，而用PrettyPrintWriter方法输出的为有分隔有一定格式的XML文件。