基础使用
基础使用
Convert Java to JSON
首先声明有一个简单的 POJO:
// Note: can use getters/setters as well; here we just use public fields directly:
public class MyValue {
public String name;
public int age;
// NOTE: if using getters/setters, can keep fields `protected` or `private`
}
然后创建一个 ObjectMapper 实例用于进行转化：
mapper.writeValue(new File("result.json"), myResultObject);
// or:
byte[] jsonBytes = mapper.writeValueAsBytes(myResultObject);
// or:
String jsonString = mapper.writeValueAsString(myResultObject);
案例：Staff
我们可以参考一个实例，将某个 Staff 的信息转化为 JSON 然后写入到文件中，首先来定义实体类：
public class Staff {
private String name;
private int age;
private String position;
private BigDecimal salary;
private List<String> skills;
//getters and setters
然后具体的将 Java 实体类转化为 JSON 的语句为：
// 构建测试对象
private Staff createDummyObject() {
Staff staff = new Staff();
staff.setName("test");
staff.setAge(33);
staff.setPosition("Developer");
staff.setSalary(new BigDecimal("7500"));
List<String> skills = new ArrayList<>();
skills.add("java");
skills.add("python");
staff.setSkills(skills);
return staff;
}
ObjectMapper mapper = new ObjectMapper();
Staff staff = createDummyObject();
try {
// Convert object to JSON string and save into a file directly
mapper.writeValue(new File("staff.json"), staff);
// Convert object to JSON string
String jsonInString = mapper.writeValueAsString(staff);
System.out.println(jsonInString);
// Convert object to JSON string and pretty print
jsonInString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(staff);
System.out.println(jsonInString);
} catch (JsonGenerationException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
最终的输出为：
{
"name": "test",
"age": 33,
"position": "Developer",
"salary": 7500,
"skills": ["java", "python"]
}
将 JSON 转化为 Java
将 JSON 转化为 Java 的实体类同样需要用到 ObjectMapper 对象：
ObjectMapper mapper = new ObjectMapper(); // create once, reuse
MyValue value = mapper.readValue(new File("data.json"), MyValue.class);
// or:
value = mapper.readValue(new URL("http://some.com/api/entry.json"), MyValue.class);
// or:
value = mapper.readValue("{\"name\":\"Bob\", \"age\":13}", MyValue.class);
而如果我们要将 JSON 转化为 Java 中的 List 或者 Map 的话，可以采用如下方式：
// 将某个 JSON 转化为数组类型
MyClass[] myObjects = mapper.readValue(json, MyClass[].class);
// 将某个 JSON 转化为 List
String json = "[{\"name\":\"test\"}, {\"name\":\"laplap\"}]";
List<Staff> list = mapper.readValue(json, new TypeReference<List<Staff>>(){});
// 将某个 JSON 转化为 Map
String json = "{\"name\":\"test\", \"age\":33}";
Map<String, Object> map = mapper.readValue(json, new TypeReference<Map<String,Object>>(){});
案例：Staff
ObjectMapper mapper = new ObjectMapper();
try {
// Convert JSON string from file to Object
Staff staff = mapper.readValue(new File("D:\\staff.json"), Staff.class);
System.out.println(staff);
// Convert JSON string to Object
String jsonInString = "{\"name\":\"test\",\"salary\":7500,\"skills\":[\"java\",\"python\"]}";
Staff staff1 = mapper.readValue(jsonInString, Staff.class);
System.out.println(staff1);
// Pretty print
String prettyStaff1 = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(staff1);
System.out.println(prettyStaff1);
} catch (JsonGenerationException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
最终的输出为：
Staff [name=test, age=33, position=Developer, salary=7500, skills=[java, python]]
Staff [name=test, age=0, position=null, salary=7500, skills=[java, python]]
{
"name" : "test",
"age" : 0,
"position" : null,
"salary" : 7500,
"skills" : [ "java", "python" ]
}