序列化与反序列化

序列化（serialization）是将对象的状态信息转换为可以存储或传输的窗体的过程。在序列化期间，对象将其当前状态写入到临时或持久性存储区。以后，可以通过从存储区中读取或反序列化对象的状态，重新创建该对象。序列化是将对象状态转换为可保持或传输的格式的过程。与序列化相对的是反序列化，它将流转换为对象。这两个过程结合起来，可以轻松地存储和传输数据。

 

下面用fastjson完成序列化与反序列化的一个例子：

要被序列化和反序列化的对象Person：

public class Person {private String name;private int age;/* * 对于下面的第二个例子,此空构造器必要,否则： com.alibaba.fastjson.JSONException:  * default constructor not found. class com.test.Person */public Person() {}public Person(String name, int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}}

下面实测序列化与反序列化结果：

import com.alibaba.fastjson.JSON;public class Serialization {public static void main(String[] args) {Person person = new Person("XiaoMing", 16);//序列化String text = JSON.toJSONString(person);System.out.println(text);//反序列化Person person1 = JSON.parseObject(text, Person.class);System.out.println(person1.getName()+","+person1.getAge());}}

结果：

{"age":16,"name":"XiaoMing"}
XiaoMing,16

如果在Person中加入另一个public类型的域变量(如public int ok;)或get方法(如public int getOk(){return 88},最终都会被序列化：

分别为：{"age":16,"name":"XiaoMing","ok":0} 、{"age":16,"name":"XiaoMing","ok":88}

要想不被序列化可加关键字transient，顾名思义就是不持久化，如publictransient ok = 99; ok字段将不会被序列化。

对于List的序列化与反序列化：

public class People {private String id;private List<Person> list = new ArrayList<Person>();public String getId() {return id;}public void setId(String id) {this.id = id;}public List<Person> getList() {return list;}public void setList(List<Person> list) {this.list = list;}}

import com.alibaba.fastjson.JSON;public class SerializationList {public static void main(String[] args) {People people = new People();people.setId("10012");Person p1 = new Person("XiaoMing", 16);Person p2 = new Person("XiaoFang", 15);List<Person> list = new ArrayList<Person>();list.add(p1);list.add(p2);people.setList(list);// 序列化String text = JSON.toJSONString(people);System.out.println(text);// 反序列化People p = JSON.parseObject(text, People.class);System.out.println(p.getId());for(Person person : p.getList()){System.out.println(person.getName()+","+person.getAge());}}}

结果：

{"id":"10012","list":[{"age":16,"name":"XiaoMing"},{"age":15,"name":"XiaoFang"}]}
10012
XiaoMing,16
XiaoFang,15

拼装json串：

JSONArray jArr = new JSONArray();nameSet = contactMap.keySet();for (String name : nameSet) {    JSONObject jobj = new JSONObject();    jobj.put("name", name);    jobj.put("phone", contactMap.get(name));    jArr.add(jobj);}String jsonStr = jArr.toJSONString();

System.out.print(jsonStr); 

[{"name":"张三","phone":"13611112222"},{"name":"李四","phone":"13733334444"}]

注意，对于极端情况，如下：

public class Ruler {

    public String name;

    public int len;

}

String rawJson1 = "{}";

String rawJson2 = "{'list':[]}";

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JSONObject jobj = JSON.parseObject(rawJson1);

Iterator<Object> it = jobj.values().iterator();

==>it.hasNext() == false

Ruler ruler = JSON.parseObject(rawJson1, Ruler.class);

==>ruler.name==null, ruler.len==0

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JSONObject jobj = JSON.parseObject(rawJson2);

JSONArray jArr = jobj .getJSONArray("list");
List<Ruler> rulers = (List<Ruler>) JSONArray.parseArray(jArr.toJSONString(), Ruler.class);
==>rulers.size()==0

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JSON.toJSONString(new Object())==>{}

JSON.toJSONString(new ArrayList())==>[]

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