# Jackson的使用 ###### tags: `SpringMVC-json` 1.使用Jackson，需要先在pom.xml導入jar包 ```xml= <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind --> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-databind</artifactId> <version>2.14.0</version> </dependency> ``` 2.配置SpringMVC的web.xml環境 ```xml= <?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <parent> <artifactId>SpringMVC</artifactId> <groupId>org.example</groupId> <version>1.0-SNAPSHOT</version> </parent> <modelVersion>4.0.0</modelVersion> <artifactId>springmvc-05-json</artifactId> <properties> <maven.compiler.source>8</maven.compiler.source> <maven.compiler.target>8</maven.compiler.target> </properties> <dependencies> <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-core --> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-databind</artifactId> <version>2.14.0</version> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <version>1.18.24</version> </dependency> </dependencies> </project> ``` 3.springmvc-servlet.xml ```xml= <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xmlns:mvc="http://www.springframework.org/schema/mvc" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/mvc https://www.springframework.org/schema/mvc/spring-mvc.xsd"> <context:component-scan base-package="com.kuang.controller"/> <mvc:default-servlet-handler /> <mvc:annotation-driven /> <!-- 视图解析器 --> <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver" id="internalResourceViewResolver"> <!-- 前缀 --> <property name="prefix" value="/WEB-INF/jsp/" /> <!-- 后缀 --> <property name="suffix" value=".jsp" /> </bean> </beans> ``` 4.編寫一個User實體類 ```java= package com.kuang.pojo; import lombok.AllArgsConstructor; import lombok.Data; import lombok.NoArgsConstructor; //需要导入lombok @Data @AllArgsConstructor @NoArgsConstructor public class User { private String name; private int age; private String sex; } ``` 5.編寫一個控制器 ```java= @Controller public class UserController { @RequestMapping("/j1") @ResponseBody //他就不會走視圖解析器，會直接返回一個字符串 public String json1(){ //創建一個對象 User user = new User("戀戀",10,"女"); return user.toString(); } } ``` 5.結果，返回toString的字符串 ![](https://i.imgur.com/cJ6VKRZ.png) ### 使用jackson ```java= @Controller public class UserController { @RequestMapping("/j1") @ResponseBody //他就不會走視圖解析器，會直接返回一個字符串 public String json1() throws JsonProcessingException { //jackson,ObjectMapper ObjectMapper mapper = new ObjectMapper(); //創建一個對象 User user = new User("戀戀",10,"女"); String str = mapper.writeValueAsString(user); return str; } } ``` #### 變成json風格的字符串(有加"") ![](https://i.imgur.com/nrnihBQ.png) ### @RestController 不走視圖解析器，直接回傳字符串 ```java= @RestController public class UserController { @RequestMapping("/j1") public String json1() throws JsonProcessingException { //jackson,ObjectMapper ObjectMapper mapper = new ObjectMapper(); //創建一個對象 User user = new User("戀戀",10,"女"); String str = mapper.writeValueAsString(user); return str; } } ``` 結果 ![](https://i.imgur.com/2oUgX7x.png) ### 呈現集合數據 ```java= @RequestMapping("/j2") // @ResponseBody public String json2() throws JsonProcessingException { //jackson,ObjectMapper ObjectMapper mapper = new ObjectMapper(); List<User> userList = new ArrayList<User>(); User user1 = new User("戀戀1",10,"女"); User user2 = new User("戀戀2",10,"女"); User user3 = new User("戀戀3",10,"女"); User user4 = new User("戀戀4",10,"女"); userList.add(user1); userList.add(user2); userList.add(user3); userList.add(user4); String str = mapper.writeValueAsString(userList); return str;// new ObjectMapper().writeValueAsString(userList); } ``` #### 結果 ![](https://i.imgur.com/KgBTwsg.png) ### 表示時間 ```java= @RequestMapping("/j3") public String json3() throws JsonProcessingException { //jackson,ObjectMapper ObjectMapper mapper = new ObjectMapper(); Date date = new Date(); //ObjectMapper，時間解析後的默認格式為：TimeStamp return mapper.writeValueAsString(date); } ``` #### 結果 ![](https://i.imgur.com/BsQ6N9T.png) ### 設置時間的格式1 ```java= @RequestMapping("/j3") public String json3() throws JsonProcessingException { //jackson,ObjectMapper ObjectMapper mapper = new ObjectMapper(); Date date = new Date(); //自定義日期的格式 SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); //ObjectMapper，時間解析後的默認格式為：TimeStamp(時間戳) return mapper.writeValueAsString(sdf.format(date)); } ``` ![](https://i.imgur.com/d0EMAkj.png) ### 使用ObjectMapper來格式化輸出 ```java= @RequestMapping("/j3") public String json3() throws JsonProcessingException { ObjectMapper mapper = new ObjectMapper(); //不使用時間戳的方式 mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false); //自定義日期的格式 SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); mapper.setDateFormat(sdf); Date date = new Date(); //ObjectMapper，時間解析後的默認格式為：TimeStamp(時間戳) return mapper.writeValueAsString(sdf.format(date)); } ``` ![](https://i.imgur.com/6F3YS18.png)