JSON数据和Java对象的相互转换要用到JSON解析器jackson
JSON解析器-------jackson是springmvc框架内置的解析器
Java对象转换JSON
- 使用步骤：使用步骤：
1. 导入jackson的相关jar包
- 创建Jackson核心对象 ObjectMapper
- 调用ObjectMapper的相关方法进行转换1. 转换方法：1 .writeValue(参数1，obj): 参数1： File：将obj对象转换为JSON字符串，并保存到指定的文件中 Writer：将obj对象转换为JSON字符串，并将json数据填充到字符输出流中 OutputStream：将obj对象转换为JSON字符串，并将json数据填充到字节输出流中2.* writeValueAsString(obj):将对象转为json字符串
- 注解： 1. @JsonIgnore：排除属性。 2. @JsonFormat：属性值得格式化 * @JsonFormat(pattern = “yyyy-MM-dd”)
- 复杂java对象转换
1. List：数组
2. Map：对象格式一致
测试如下
JSON转为Java对象
- 导入jackson的相关jar包
- 创建Jackson核心对象 ObjectMapper
- 调用ObjectMapper的相关方法进行转换
1. readValue(json字符串数据,Class)
注意：
map对象写法
Map<String,Object> map = new HashMap<String,Object>();
map.put(“name”,“张三”);
list集合写法
//创建List集合
List ps = new ArrayList();
ps.add§;
package cn.itcast.test; import cn.itcast.domain.Person; import com.fasterxml.jackson.databind.ObjectMapper; import org.junit.Test; import java.io.FileWriter; import java.util.*; public class JacksonTest { //Java对象转为JSON字符串 @Test public void test1() throws Exception { //1.创建Person对象 Person p = new Person(); p.setName("张三"); p.setAge(23); p.setGender("男"); //2.创建Jackson的核心对象 ObjectMapper ObjectMapper mapper = new ObjectMapper(); //3.转换 /* 转换方法： writeValue(参数1，obj): 参数1： File：将obj对象转换为JSON字符串，并保存到指定的文件中 Writer：将obj对象转换为JSON字符串，并将json数据填充到字符输出流中 OutputStream：将obj对象转换为JSON字符串，并将json数据填充到字节输出流中 writeValueAsString(obj):将对象转为json字符串 */ String json = mapper.writeValueAsString(p); //{"name":"张三","age":23,"gender":"男"} //System.out.println(json);//{"name":"张三","age":23,"gender":"男"} //writeValue，将数据写到d://a.txt文件中 //mapper.writeValue(new File("d://a.txt"),p); //writeValue.将数据关联到Writer中 mapper.writeValue(new FileWriter("d://b.txt"),p); } @Test public void test2() throws Exception { //1.创建Person对象 Person p = new Person(); p.setName("张三"); p.setAge(23); p.setGender("男"); p.setBirthday(new Date()); //2.转换 ObjectMapper mapper = new ObjectMapper(); String json = mapper.writeValueAsString(p); System.out.println(json);//{"name":"张三","age":23,"gender":"男","birthday":1530958029263} //{"name":"张三","age":23,"gender":"男","birthday":"2018-07-07"} } @Test public void test3() throws Exception { //1.创建Person对象 Person p = new Person(); p.setName("张三"); p.setAge(23); p.setGender("男"); p.setBirthday(new Date()); Person p1 = new Person(); p1.setName("张三"); p1.setAge(23); p1.setGender("男"); p1.setBirthday(new Date()); Person p2 = new Person(); p2.setName("张三"); p2.setAge(23); p2.setGender("男"); p2.setBirthday(new Date()); //创建List集合 List<Person> ps = new ArrayList<Person>(); ps.add(p); ps.add(p1); ps.add(p2); //2.转换 ObjectMapper mapper = new ObjectMapper(); String json = mapper.writeValueAsString(ps); // [{},{},{}] //[{"name":"张三","age":23,"gender":"男","birthday":"2018-07-07"},{"name":"张三","age":23,"gender":"男","birthday":"2018-07-07"},{"name":"张三","age":23,"gender":"男","birthday":"2018-07-07"}] System.out.println(json); } @Test public void test4() throws Exception { //1.创建map对象 Map<String,Object> map = new HashMap<String,Object>(); map.put("name","张三"); map.put("age",23); map.put("gender","男"); //2.转换 ObjectMapper mapper = new ObjectMapper(); String json = mapper.writeValueAsString(map); //{"name":"张三","age":23,"gender":"男"} System.out.println(json);//{"gender":"男","name":"张三","age":23} } //演示 JSON字符串转为Java对象 @Test public void test5() throws Exception { //1.初始化JSON字符串 String json = "{\"gender\":\"男\",\"name\":\"张三\",\"age\":23}"; //2.创建ObjectMapper对象 ObjectMapper mapper = new ObjectMapper(); //3.转换为Java对象 Person对象 Person person = mapper.readValue(json, Person.class); System.out.println(person); } }
