jackson的应用

直接上代码

 package com.demo.jackson.utils;

 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.DeserializationFeature;
 import com.fasterxml.jackson.databind.JavaType;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.util.StringUtils;

 @Slf4j
 public class JsonUtil {
     private static ObjectMapper objectMapper = new ObjectMapper();
     static {
         //忽略 在json字符串中存在，但是在java对象中不存在对应属性的情况。防止错误
         objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
     }

     /**
      * 对象转换成Sting
      * @param obj
      * @param <T>
      * @return
      */
     public static <T> String obj2String(T obj){
         if (obj == null) {
             return null;
         }
         try {
             return obj instanceof String ? (String) obj : objectMapper.writeValueAsString(obj);
         } catch (JsonProcessingException e) {
             System.out.println("Parse Object to String error");
             e.printStackTrace();
             return null;
         }
     }
     /**
      * 规范地将对象转换成Sting
      * @param obj
      * @param <T>
      * @return
      */
     public static <T> String obj2StringPretty(T obj){
         if(obj == null){
             return null;
         }
         try {
             return obj instanceof String ? (String)obj :  objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(obj);
         } catch (Exception e) {
             log.warn("Parse Object to String error",e);
             return null;
         }
     }

     /**
      * String转换成obj对象
      * @param str
      * @param clazz
      * @param <T>
      * @return
      */
     public  static <T> T str2Obj(String str, Class<T> clazz){
         if(str==null){
             return null;
         }
         try {
             return clazz.equals(String.class) ? (T) str : objectMapper.readValue(str, clazz);
         } catch (Exception e) {
             e.printStackTrace();
             return null;
         }
     }

     /**
      * String转换成对象
      * @param str
      * @param typeReference
      * @param <T>
      * @return
      */
     public static <T> T string2Obj(String str, TypeReference<T> typeReference){
         if(StringUtils.isEmpty(str) || typeReference == null){
             return null;
         }
         try {
             return (T)(typeReference.getType().equals(String.class)? str : objectMapper.readValue(str,typeReference));
         } catch (Exception e) {
             log.warn("Parse String to Object error",e);
             return null;
         }
     }

     /**
      * String转换成对象
      * @param str
      * @param collectionClass
      * @param elementClasses
      * @param <T>
      * @return
      */
     public static <T> T string2Obj(String str, Class<?> collectionClass, Class<?>... elementClasses){
         JavaType javaType = objectMapper.getTypeFactory().constructParametricType(collectionClass,elementClasses);
         try {
             return objectMapper.readValue(str,javaType);
         } catch (Exception e) {
             log.warn("Parse String to Object error",e);
             return null;
         }
     }
 }

测试：

 package com.demo.jackson.test;

 import com.demo.jackson.entity.Student;
 import com.demo.jackson.utils.JsonUtil;
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import org.junit.Test;

 import java.util.*;

 @SuppressWarnings("ALL")
 public class JacksonTest {
     /**
      * 序列化
      */
     @Test
     public void test01(){
         Student s = new Student();
         s.setName("cjj");
         s.setAge(22);
         s.setProfileImageUrl("link");
         String s1 = JsonUtil.obj2String(s);
         System.out.println(s1);

         Map<String, List<Integer>> map = new HashMap<>();
         map.put("a", Arrays.asList(1, 2, 3));
         map.put("b", Arrays.asList(1, 2, 3));
         String result1 = JsonUtil.obj2StringPretty(map);
         System.out.println(result1);
     }

     /**
      * 反序列化
      */
     @Test
     public void Test02(){
         String str = "{\"name\":\"name\",\"age\":10,\"profileImageUrl\":\"link\"}";
         Student student = JsonUtil.str2Obj(str, Student.class);
         System.out.println(student);
     }
     @Test
     public void test03() throws Exception {

         Student student1 = new Student();
         student1.setAge(10);
         student1.setName("name1");
         student1.setProfileImageUrl("link1");

         Student student2 = new Student();
         student2.setAge(20);
         student2.setName("name2");
         student2.setProfileImageUrl("link2");

         List<Student> studentList = new ArrayList<>();
         studentList.add(student1);
         studentList.add(student2);
         String result = JsonUtil.obj2String(studentList);
         // [{"name":"name1","age":10,"profileImageUrl":"link1"},{"name":"name2","age":20,"profileImageUrl":"link2"}]
         System.out.println(result);

         List<Student> finalList = JsonUtil.string2Obj(result, new TypeReference<List<Student>>() {});
         // [{name=name1, age=10, profileImageUrl=link1}, {name=name2, age=20, profileImageUrl=link2}]
         System.out.println(finalList);
     }
     @Test
     public void test04() throws Exception {

         Student student1 = new Student();
         student1.setAge(10);
         student1.setName("name1");
         student1.setProfileImageUrl("link1");

         Student student2 = new Student();
         student2.setAge(20);
         student2.setName("name2");
         student2.setProfileImageUrl("link2");

         List<Student> studentList = new ArrayList<>();
         studentList.add(student1);
         studentList.add(student2);
         String result = JsonUtil.obj2String(studentList);
         // [{"name":"name1","age":10,"profileImageUrl":"link1"},{"name":"name2","age":20,"profileImageUrl":"link2"}]
         System.out.println(result);

         List<Student> finalList = JsonUtil.string2Obj(result, List.class, Student.class);
         // [{name=name1, age=10, profileImageUrl=link1}, {name=name2, age=20, profileImageUrl=link2}]
         System.out.println(finalList);
     }
     @Test
     public void jsonProperty() throws Exception {

         String str = "{\"name\":\"name\",\"age\":10,\"setImage\":\"link\"}";
         Student student1 = JsonUtil.string2Obj(str, Student.class);
         // name
         System.out.println(student1.getName());
         //
         System.out.println(student1.getAge());
         // link
         System.out.println(student1.getProfileImageUrl());
         // {"name":"name","age":10,"getImage":"link"}
         System.out.println(JsonUtil.obj2String(student1));
     }

     /**
      * 除了将json转为对象外，还可以用Tree Mode方式解析JSON，全程无脑操作，
      * 除了一些特别复杂的JSON，或者只取JSON中的一部分，千万不要用这种二B方式解析JSON。
      * 正确的方式是将JSON直接转为对象。
      * @throws Exception
      */
     @Test
     public void parseJson() throws Exception {
         String jsonStr = "{\"name\":\"zhansan\",\"age\":100,\"schools\":[{\"name\":\"tsinghua\",\"location\":\"beijing\"},{\"name\":\"pku\",\"location\":\"beijing\"}]}";

         ObjectMapper objectMapper = new ObjectMapper();
         JsonNode jsonNode = objectMapper.readTree(jsonStr);

         String name = jsonNode.get("name").asText();
         int age = jsonNode.get("age").asInt();
         // name is zhansan age is 100
         System.out.println("name is " + name + " age is " + age);

         JsonNode schoolsNode = jsonNode.get("schools");
         for (int i = 0; i < schoolsNode.size(); i++) {
             String schooleName = schoolsNode.get(i).get("name").asText();
             String schooleLocation = schoolsNode.get(i).get("location").asText();
             // schooleName is tsinghua schooleLocation is beijing
             // schooleName is pku schooleLocation is beijing
             System.out.println("schooleName is " + schooleName + " schooleLocation is " + schooleLocation);
         }
     }
 }