8 fastJson的使用

Fastjson介绍

Fastjson是一个Java语言编写的JSON处理器,由阿里巴巴公司开发。
1、遵循http://json.org标准，为其官方网站收录的参考实现之一。
2、功能qiang打，支持JDK的各种类型，包括基本的JavaBean、Collection、Map、Date、Enum、泛型。
3、无依赖，不需要例外额外的jar，能够直接跑在JDK上。
4、开源，使用Apache License 2.0协议开源。http://code.alibabatech.com/wiki/display/FastJSON/Home
5、具有超高的性能，java世界里没有其他的json库能够和fastjson可相比了。

如果获得Fastjson？
SVN:http://code.alibabatech.com/svn/fastjson/trunk/
WIKI:http://code.alibabatech.com/wiki/display/FastJSON/Home
Issue Tracking:http://code.alibabatech.com/jira/browse/FASTJSON

如果你使用了Maven，maven repository配置如下：

<repository>
	<id>opensesame</id>
	<name>Alibaba OpenSource Repsoitory</name>
	<url>http://code.alibabatech.com/mvn/releases/</url>
	<snapshots>
		<enabled>false</enabled>
	</snapshots>
</repository>

pom.xml文件中加入依赖依赖：

<dependency>
	<groupId>com.alibaba</groupId>
	<artifactId>fastjson</artifactId>
	<version>1.2.9</version>
</dependency>

如果没有使用maven，可以直接下载：

Binary : http://code.alibabatech.com/mvn/releases/com/alibaba/fastjson/1.1.1/fastjson-1.1.1.jar
Source :http://code.alibabatech.com/mvn/releases/com/alibaba/fastjson/1.1.1/fastjson-1.1.1-sources.jar
Subversion : http://code.alibabatech.com/svn/fastjson/

使用介绍：
Fastjson的最主要的使用入口是com.alibaba.fastjson.JSON

import com.alibaba.fastjson.JSON;

public static final Object parse(String text); // 把JSON文本parse为JSONObject或者JSONArray
public static final JSONObject parseObject(String text)； // 把JSON文本parse成JSONObject
public static final <T> T parseObject(String text, Class<T> clazz); // 把JSON文本parse为JavaBean
public static final JSONArray parseArray(String text); // 把JSON文本parse成JSONArray
public static final <T> List<T> parseArray(String text, Class<T> clazz); //把JSON文本parse成JavaBean集合
public static final String toJSONString(Object object); // 将JavaBean序列化为JSON文本
public static final String toJSONString(Object object, boolean prettyFormat); // 将JavaBean序列化为带格式的JSON文本
public static final Object toJSON(Object javaObject); 将JavaBean转换为JSONObject或者JSONArray。

使用例子：

两个基础类：

 public class Student {
     private int id;

     private String name;

     /**
      * 默认的构造方法必须不能省，不然不能通过json字符串解析成java对象
      */
     public Student() {
     }

     public Student(int id, String name) {
         this.id = id;
         this.name = name;
     }

     public int getId() {
         return id;
     }

     public void setId(int id) {
         this.id = id;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }
 }

 public class Teacher {
     private int id;

     private String name;

     private List<Student> stus;
     /**
      * 默认的构造方法必须不能省，不然不能通过json字符串解析成java对象
      */
     public Teacher() {
     }

     public Teacher(int id, String name) {
         this.id = id;
         this.name = name;
     }

     public int getId() {
         return id;
     }

     public void setId(int id) {
         this.id = id;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public List<Student> getStus() {
         return stus;
     }

     public void setStus(List<Student> stus) {
         this.stus = stus;
     }

     public void addStudent(Student stu){
         this.stus.add(stu);
     }

     public void addStudents(List<Student> stus){
         for (Student stu : stus) {
             this.stus.add(stu);
         }
     }

     public void setStudents(List<Student> stus){
         this.stus=stus;
     }
 }

 public class JsonTest1 {
     public static void main(String[] args) {
         Student stu=new Student(1,"one");
         //java实例转化成json字符串
         String jsonStr=test1(stu);
         print();
         //json字符串转成java实例
         stu=test2(jsonStr);
         print();
         //集合转成json字符串
         jsonStr=test3();
         print();

         //复杂集合转成json字符串
         test4();
         print();

     }
     //java实例转化成json字符串
     public static String test1(Student stu){
         String jsonStr=JSON.toJSONString(stu);
         System.out.println(jsonStr);
         return jsonStr;
     }

     //json字符串转成java实例
     public static Student test2(String jsonStr){
         Student stu=JSON.parseObject(jsonStr,Student.class);
         System.out.println("转换前json字符串："+jsonStr);
         System.out.println("转换后：id="+stu.getId()+",name="+stu.getName());
         return stu;
     }

     //集合转成json字符串
     public static String test3(){
         List<Student> list=new ArrayList<Student>();
         for(int i=1;i<=3;i++){
             list.add(new Student(i,"name "+i));
         }
         String jsonStr=JSON.toJSONString(list);
         System.out.println(jsonStr);
         return jsonStr;
     }

     //复杂集合转成json字符串
     public static String test4(){
         List<Teacher> teaList = new ArrayList<Teacher>();
         long time = System.currentTimeMillis();
         for(int i=0;i<10;i++) {
             Teacher teacher = new Teacher(i, "Teacher " + i);
             List<Student> stus = new ArrayList<Student>();
             for(int j = 0 ;j<4;j++) {
                 Student s = new Student(j, "Student" + j);
                 stus.add(s);
             }
             teacher.setStudents(stus);
             teaList.add(teacher);
         }
         //true表示按照json格式输出
         String jsonStr = JSON.toJSONString(teaList,true);
         System.out.println(jsonStr);
         return jsonStr;
     }
     public static void print(){
         System.out.println("....................................");
     }
 }

输出结果：

{"id":1,"name":"one"}
....................................
转换前json字符串：{"id":1,"name":"one"}
转换后：id=1,name=one
....................................
[{"id":1,"name":"name 1"},{"id":2,"name":"name 2"},{"id":3,"name":"name 3"}]
....................................
[
    {
        "id":0,
        "name":"Teacher 0",
        "stus":[
            {
                "id":0,
                "name":"Student0"
            },
            {
                "id":1,
                "name":"Student1"
            },
            {
                "id":2,
                "name":"Student2"
            },
            {
                "id":3,
                "name":"Student3"
            }
        ]
    },
    {
        "id":1,
        "name":"Teacher 1",
        "stus":[
            {
                "id":0,
                "name":"Student0"
            },
            {
                "id":1,
                "name":"Student1"
            },
            {
                "id":2,
                "name":"Student2"
            },
            {
                "id":3,
                "name":"Student3"
            }
        ]
    },
    {
        "id":2,
        "name":"Teacher 2",
        "stus":[
            {
                "id":0,
                "name":"Student0"
            },
            {
                "id":1,
                "name":"Student1"
            },
            {
                "id":2,
                "name":"Student2"
            },
            {
                "id":3,
                "name":"Student3"
            }
        ]
    },
    {
        "id":3,
        "name":"Teacher 3",
        "stus":[
            {
                "id":0,
                "name":"Student0"
            },
            {
                "id":1,
                "name":"Student1"
            },
            {
                "id":2,
                "name":"Student2"
            },
            {
                "id":3,
                "name":"Student3"
            }
        ]
    },
    {
        "id":4,
        "name":"Teacher 4",
        "stus":[
            {
                "id":0,
                "name":"Student0"
            },
            {
                "id":1,
                "name":"Student1"
            },
            {
                "id":2,
                "name":"Student2"
            },
            {
                "id":3,
                "name":"Student3"
            }
        ]
    },
    {
        "id":5,
        "name":"Teacher 5",
        "stus":[
            {
                "id":0,
                "name":"Student0"
            },
            {
                "id":1,
                "name":"Student1"
            },
            {
                "id":2,
                "name":"Student2"
            },
            {
                "id":3,
                "name":"Student3"
            }
        ]
    },
    {
        "id":6,
        "name":"Teacher 6",
        "stus":[
            {
                "id":0,
                "name":"Student0"
            },
            {
                "id":1,
                "name":"Student1"
            },
            {
                "id":2,
                "name":"Student2"
            },
            {
                "id":3,
                "name":"Student3"
            }
        ]
    },
    {
        "id":7,
        "name":"Teacher 7",
        "stus":[
            {
                "id":0,
                "name":"Student0"
            },
            {
                "id":1,
                "name":"Student1"
            },
            {
                "id":2,
                "name":"Student2"
            },
            {
                "id":3,
                "name":"Student3"
            }
        ]
    },
    {
        "id":8,
        "name":"Teacher 8",
        "stus":[
            {
                "id":0,
                "name":"Student0"
            },
            {
                "id":1,
                "name":"Student1"
            },
            {
                "id":2,
                "name":"Student2"
            },
            {
                "id":3,
                "name":"Student3"
            }
        ]
    },
    {
        "id":9,
        "name":"Teacher 9",
        "stus":[
            {
                "id":0,
                "name":"Student0"
            },
            {
                "id":1,
                "name":"Student1"
            },
            {
                "id":2,
                "name":"Student2"
            },
            {
                "id":3,
                "name":"Student3"
            }
        ]
    }
]
....................................

如果对类中有些字段不解析，可以通过SimplePropertyPreFilter来选取需要需要解析的属性，例子如下：

  //类中有个别字段不解析
     public static void test5(){
         Student stu=new Student(1,"one");
         SimplePropertyPreFilter filter=new SimplePropertyPreFilter(Student.class,"id");
         String jsonStr=JSON.toJSONString(stu,filter);
         System.out.println(jsonStr);
     }

输出结果：

{"id":1}

把list集合的json字符串反序列为list集合：

     public static void test6(){
         List<Student> students = new ArrayList<Student>();
         for(int i=0;i<5;i++) {
             Student stu = new Student(i, "Student" + i);
             students.add(stu);
         }
         // 过滤哪些属性需要转换
 //      SimplePropertyPreFilter filter = new SimplePropertyPreFilter(Student.class, "id","age");
 //      String jsonStu =JSON.toJSONString(students,filter);
         String jsonStu =JSON.toJSONString(students);
         System.out.println(jsonStu);

         List<Student> stu =JSON.parseObject(jsonStu, new TypeReference<List<Student>>(){});
         for(int i=0;i<stu.size();i++)
         {
             System.out.println(stu.get(i));
         }
     }

代码输出：

[{"id":0,"name":"Student0"},{"id":1,"name":"Student1"},{"id":2,"name":"Student2"},{"id":3,"name":"Student3"},{"id":4,"name":"Student4"}]
com.main.etl.server.json.Student@60682430
com.main.etl.server.json.Student@551ffcc2
com.main.etl.server.json.Student@270b5037
com.main.etl.server.json.Student@57bf5ee7
com.main.etl.server.json.Student@54efbcb2