FastJson：JSON JSONObject JSONArray详解以及SimplePropertyPreFilter 的介绍

FastJson是阿里巴巴开发的一款专门用于Java开发的包，实现Json对象，JavaBean对，Json字符串之间的转换。

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一、JSON对象介绍

JSON的特点如下：

1. 数据在花括号中。
2. 数据以"键：值"对的形式出现（其中键多以字符串形式出现，值可取字符串，数值，甚至其他json对象）。
3. 每两个"键:值"对以逗号分隔（最后一个"键：值"对省略逗号）。

例：

普通Json对象
{"ID": 1001,"name": "张三","age": 24
​}
数组Json对象
[{"ID": 1001, "name": "张三", "age": 24},{"ID": 1002, "name": "李四", "age": 25},{"ID": 1003, "name": "王五", "age": 22}
]复杂Json对象
{"部门名称":"研发部","部门成员":[{"ID": 1001, "name": "张三", "age": 24},{"ID": 1002, "name": "李四", "age": 25},{"ID": 1003, "name": "王五", "age": 22}],"部门位置":"xx楼21号"
}

二、FastJson-JSON

JSON是一个抽象类并且实现了JSONStreamAware, JSONAware接口，提供了JSON转换的方法（详细方法说明看后文）。

JSON多用于JavaBean->JSONString 或者 JSONString->javaJSON

@Builder
@Data
@AllArgsConstructor
@NoArgsConstructor
public class StudentEntity {@JSONField(name = "student_name",ordinal = 1)private String name;@JSONField(name = "student_age",ordinal = 2)private Integer age;
}

 @Testpublic void beanJsonTest() {StudentEntity student = StudentEntity.builder().name("张三").age(18).build();String jsonStudentString = JSON.toJSONString(student); //{"student_name":"张三","student_age":18}StudentEntity studentObject = JSON.parseObject(jsonStudentString, StudentEntity.class);  //转为java对象}

三、FastJson-JSONObject

JSONObject继承了JSON并实现了Map接口。

底层是个Map集合，多用于操作JSONObject 如取属性等，Map集合的功能也都有。

@Builder
@Data
@AllArgsConstructor
@NoArgsConstructor
public class StudentEntity {@JSONField(name = "student_name",ordinal = 1)private String name;@JSONField(name = "student_age",ordinal = 2)private Integer age;
}

 @Testpublic void beanJsonTest() {StudentEntity student = StudentEntity.builder().name("张三").age(18).build();String jsonStudentString = JSON.toJSONString(student); //{"student_name":"张三","student_age":18}/**Map<String,Object> map = new HashMap<>();map.put("student_name", "李四");map.put("student_age", 19);map.put("date",students);JSONObject jsonObject = new JSONObject(map);**/JSONObject jsonObject = JSONObject.parseObject(jsonStudentString); //{"student_name":"张三","student_age":18}jsonObject.put("student_name", "李四");jsonObject.put("student_age", 19);//{"student_name":"李四","student_age":19}jsonObject.put("date",student);//{"student_name":"张三","student_age":18,"date":[{"student_name":"张三","student_age":18},{"student_name":"张三","student_age":18},{"student_name":"张三","student_age":18}]}//get方法  根据key取出valueStudentEntity date = jsonObject.getObject("date", StudentEntity.class);String studentName = jsonObject.getObject("student_name", String.class);jsonObject.getString("student_name");}

四、FastJson-JSONArray

JSONObject继承了JSON并实现了List接口。

底层是个ArrayList，多用于用于操作JSONArray 比如遍历等，通常与JSONObject联合使用。

@Builder
@Data
@AllArgsConstructor
@NoArgsConstructor
public class StudentEntity {@JSONField(name = "student_name",ordinal = 1)private String name;@JSONField(name = "student_age",ordinal = 2)private Integer age;
}

    @Testpublic void twoTest3() {StudentEntity student1 = StudentEntity.builder().name("张三").age(18).build();StudentEntity student2 = StudentEntity.builder().name("张三").age(18).build();StudentEntity student3 = StudentEntity.builder().name("张三").age(18).build();ArrayList<StudentEntity> students = Lists.newArrayList(student1, student2, student3);JSONArray jsonArray = JSONArray.parseArray(JSON.toJSONString(students));jsonArray.forEach(item -> {String jsonStudentStringItem = JSONObject.toJSONString(item);System.out.println(jsonStudentStringItem);});//{"student_name":"张三","student_age":18}//{"student_name":"张三","student_age":18}//{"student_name":"张三","student_age":18}JSONObject StudentJson = new JSONObject();StudentJson.put("Student",jsonArray);System.out.println(StudentJson.toJSONString());}

五、常用方法汇总

常用方法

  /*** FastJson常用方法*/@Testpublic void fastJSONTest() {StudentEntity student = StudentEntity.builder().name("张三").age(18).build();//1.JSON常用方法//1.1  toJSONString ：将java对象转为JSONStringString jsonStudentString = JSON.toJSONString(student);//{"student_name":"张三","student_age":18}//1.2  parseObject ：将JSONString转为java对象StudentEntity studentObject = JSON.parseObject(jsonStudentString, StudentEntity.class);//StudentEntity(name=张三, age=18)// 1.3 JSONtoJSONBytes()：将 Java 对象序列化为 JSON 字节数组byte[] jsonStudentStringBytes = JSON.toJSONBytes(student);//[123, 34, 115, 116, 117, 100, 101, 110, 116, 95, 110, 97, 109, 101, 34, 58, 34, 228, 189, 254, 228, 184, 230, 34, 44, 34,115, 116, 117, 100, 101, ]//1.4 JSONparseBytes()：将 JSON 字节数组反序列化为 Java 对象StudentEntity studentObject2 = JSON.parseObject(jsonStudentStringBytes, StudentEntity.class);//1.5 JSON.parseObject：将Java对象转为JSONObjectJSONObject jsonObject = JSON.parseObject(jsonStudentString);//2.JSONObject常用方法 JSONObject继承了JSON类,并实现了Map接口，所以可以调用JSON类中的方法，并且重写了Map相关方法//2.1 JSONObject.toJSONString()：将JSONObject转为JSONStringString jsonStudentString2 = jsonObject.toJSONString();//{"student_name":"张三","student_age":18}//2.2 JSONObject.put()：根据key设置valuejsonObject.put("STUDENT", StudentEntity.builder().name("王五").age(22).build());//{"student_name":"张三","student_age":18,"STUDENT":{"student_name":"王五","student_age":22}}//2.3 JSONObject.getXxx()：根据key取出valueString studentName = jsonObject.getString("student_name");//张三Integer studentAge = jsonObject.getInteger("student_age");//18/* String name = jsonObject.getObject("name", String.class);Integer age = jsonObject.getObject("age", Integer.class);*/StudentEntity studentObject3 = jsonObject.getObject("STUDENT", StudentEntity.class);//StudentEntity(name=王五, age=22)//2.4 toJavaObject：将JSONObject转为Java对象StudentEntity javaObject = jsonObject.toJavaObject(StudentEntity.class);//2.5 putAll()：合并两个JSONObjectString json1 = "{\"name\":\"Jack\"}";String json2 = "{\"age\":35}";JSONObject jsonObject1 = JSON.parseObject(json1);JSONObject jsonObject2 = JSON.parseObject(json2);JSONObject jsonObject3 = new JSONObject();jsonObject3.putAll(jsonObject1);jsonObject3.putAll(jsonObject2);//{"name":"Jack","age":35}//2.6 isEmpty()：判断JSONObject是否为空boolean empty = jsonObject.isEmpty();//containsKey() keySet() vlues() clear() remove() containsValue() 跟Map集合的方法一样 不在列举//3.JSONArray常用方法//3.1. parseArray：将Java对象转为JSONArrayStudentEntity student1 = StudentEntity.builder().name("张三1").age(18).build();StudentEntity student2 = StudentEntity.builder().name("张三2").age(18).build();StudentEntity student3 = StudentEntity.builder().name("张三3").age(18).build();ArrayList<StudentEntity> studentEntities = Lists.newArrayList(student1, student2, student3);JSONArray jsonArray = JSONArray.parseArray(JSON.toJSONString(studentEntities));//[{"student_name":"张三1","student_age":18},{"student_name":"张三2","student_age":18},{"student_name":"张三3","student_age":18}]//3.2. toJSONString()：将JSONArray转为JSONStringString jsonArrayString = jsonArray.toJSONString();//"[{"student_name":"张三1","student_age":18},{"student_name":"张三2","student_age":18},{"student_name":"张三3","student_age":18}]//3.3. toJavaObject()：将JSONArray转为Java对象List<StudentEntity> studentEntities1 = jsonArray.toJavaList(StudentEntity.class);// forEach()，fparallelStream()，stream()，spliterator()，iterator()，sort()，get()这些Arraylist方法同样都有，不在列举}

简单说一下FastJSON的JSON过滤器

SimplePropertyPreFilter 简单过滤器

class Person {public String name;public int age;
}

@Testpublic void toJSONStringWithFilterExample() {Person person = new Person();person.name = "Eve";person.age = 40;// SimplePropertyPreFilter类 实现 JSON字符串过滤SimplePropertyPreFilter simplePropertyPreFilter1 = new SimplePropertyPreFilter();//添加过滤字段simplePropertyPreFilter1.getExcludes().add("age");//不包括 "age" 字段//调用toJSONString将Java转String时传入过滤器System.out.println(JSON.toJSONString(person, simplePropertyPreFilter1));//{"name":"Eve"}//或者SimplePropertyPreFilter simplePropertyPreFilter2 = new SimplePropertyPreFilter();//添加保留字段simplePropertyPreFilter2.getIncludes().add("name");//包括 "name" 字段//调用toJSONString将Java转String时传入过滤器System.out.println(JSON.toJSONString(person, simplePropertyPreFilter2));//{"name":"Eve"}
}

自定义过滤器
FastJson提供的简单过滤器很多时候无法满足我们需求，这个时候就可以自定义管理器

@Testpublic void toJSONStringWithFilterExample2() {Person person = new Person();//1.实现 ValueFilter 接口 重写 process 方法ValueFilter filter = (object, name, value) -> {if (name.equals("age")) {return null; // 不包括 "age" 字段}return value;};// 2.实现 PropertyFilter 接口 重写 apply 方法PropertyFilter filter2 = (object, name, value) -> {if (name.equals("age")) {return false; // 不包括 "age" 字段}return true;};String jsonString1 = JSON.toJSONString(person, filter);//{"name":"Eve"}String jsonString2 = JSON.toJSONString(person, filter2);//{"name":"Eve"}}

当然还可以根据管理器实现原来去手搓来增填功能，深入了解推荐一篇文章
API接口使用Jackson序列化JSON数据动态过滤字段