Java中常用解析工具jackson及fastjson的使用
一、maven安装jackson依赖
<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind --> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-databind</artifactId> <version>2.12.3</version> </dependency>
二、Jackson的使用
实体类转化JSON
把实体类转化为JSON格式数据,返回给前端
创建 ObjectMapper obj = new ObjectMapper(); 对象,对象的 writeValueAsString 方法 会把一个实体类(必须有get、set方法)转化为JSON对象。
package com.lxc.springboot.controller; import com.fasterxml.jackson.databind.ObjectMapper; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RestController; @RestController // 这个类下边的所有方法,都会返回json,不会返回一个视图! public class Json { @RequestMapping(value = "/json") public String json() throws Exception{ User user = new User("吕星辰", "888", 20); ObjectMapper obj = new ObjectMapper(); String jsonObject = obj.writeValueAsString(user); return jsonObject; } // 为测试方便,在这里写一个实体类 public static class User { private String userName; public String getUserName() { return userName; } public void setUserName(String userName) { this.userName = userName; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } private String password; private int age; public User(String userName, String password, int age) { this.userName = userName; this.password = password; this.age = age; } } }
测试:
集合转化JSON
前端结果是:一个数组,里边是一个个对象
package com.lxc.springboot.controller; import com.fasterxml.jackson.databind.ObjectMapper; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RestController; import java.util.ArrayList; import java.util.List; @RestController public class Json { @RequestMapping(value = "/json") public String json() throws Exception{ // 创建一个集合 List<User> userList = new ArrayList<>(); for(int i = 0; i < 3; i ++) { userList.add(new User("用户名"+i, "密码"+i, 20+i)); } ObjectMapper obj = new ObjectMapper(); String jsonObject = obj.writeValueAsString(userList); return jsonObject; } // 上边有实体类,这里省略 }
测试:
Map转化JSON
@RestController public class Json { @RequestMapping(value = "/json") public String json() throws Exception{ // 创建一个Map Map<String, Object> map = new HashMap<>(); map.put("name", "测试名"); map.put("age", 20); ObjectMapper obj = new ObjectMapper(); String jsonObject = obj.writeValueAsString(map); return jsonObject; } }
前端结果是:对象
new Date() 转化JSON
@RestController public class Json { @RequestMapping(value = "/json") public String json() throws Exception{ Date date = new Date(); ObjectMapper obj = new ObjectMapper(); String jsonObject = obj.writeValueAsString(date); return jsonObject; } }
前端结果是:时间戳
当然,也可以自定义时间格式
@RestController public class Json { @RequestMapping(value = "/json") public String json() throws Exception{ Date date = new Date(); SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss"); String time = sdf.format(date); // "2021-06-27 05:19:33" ObjectMapper obj = new ObjectMapper(); String jsonObject = obj.writeValueAsString(time); return jsonObject; } }
封装
package com.lxc.springboot.utils; import com.fasterxml.jackson.core.JsonProcessingException; import com.fasterxml.jackson.databind.ObjectMapper; import com.fasterxml.jackson.databind.SerializationFeature; import java.text.SimpleDateFormat; public class JavaUtils { /** * 使用下边方法需要导入依赖包: * <dependency> * <groupId>com.fasterxml.jackson.core</groupId> * <artifactId>jackson-databind</artifactId> * <version>2.12.3</version> * </dependency> * * @param object 集合(List)、Map(HashMap)、对象(new Date) * @param format 时间格式化 yyyy-MM-dd hh:mm:ss * @return JSON格式化的字符串 */ public static String getJson(Object object, String format) { ObjectMapper objectMapper = new ObjectMapper(); // 不使用时间戳的方式 objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false); // 自定义时间格式 SimpleDateFormat sdf = new SimpleDateFormat(format); // 设置时间格式化 objectMapper.setDateFormat(sdf); try { String jsonValue = objectMapper.writeValueAsString(object); return jsonValue; } catch (JsonProcessingException e) { e.printStackTrace(); } return null; } public static String getJson(Object object) { return getJson(object, "yyyy-MM-dd hh:mm:ss"); } }
二、FastJson的使用
使用maven导入依赖包
<!--下边依赖跟aop没关系,只是项目中用到了 JSONObject,所以引入fastjson--> <dependency> <groupId>com.alibaba</groupId> <artifactId>fastjson</artifactId> <version>1.2.70</version> </dependency>
常用方法:
(1)JSON.toJSONString(obejct) - java对象转JSON字符串
(2)JSON.parseObject(string, User.class) - JSON字符串转java对象
使用
@RestController public class Json { @RequestMapping(value = "/json") public String json() throws Exception{ List<User> userList = new ArrayList<>(); userList.add(new User("1", "1", 20)); String res = JSON.toJSONString(userList); return res; }
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