JSON数据与Java对象的相互转换
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JSON数据与Java对象的相互转换
JSON解析器
常见的解析器:Jsonlib 、Gson、 fastjson、 jackson
JSON转化为Java对象
使用步骤:
1、导入jackson的相关jar包 2、创建jackson核心对象ObjectMapper 3、使用ObjectMapper的相关方法进行转换 1、readValue(json字符串数组,Class)
Java转化为JSON对象
使用步骤
1、导入jackson的相关jar包 2、创建jackson核心对象ObjectMapper 3、使用ObjectMapper的相关方法进行转换
转换方式:
* 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
注解
- @JsonIgnore:排除属性。
@JsonFormat:属性值得格式化
- @JsonFormat(pattern = "yyyy-MM-dd")
- 复杂Java对象转换
- List:数组
- Map:对象格式一致
创建person类
public class Person
private String name;
private Integer age;
private String gender;
//@JsonIgnore //忽略该属性
@JsonFormat(pattern = "yyyy-MM-dd")//属性格式化
private Date birthday;
public Date getBirthday()
return birthday;
public void setBirthday(Date birthday)
this.birthday = birthday;
public Person()
@Override
public String toString()
return "Person" +
"name='" + name + '\\'' +
", age=" + age +
", gender='" + gender + '\\'' +
'';
public String getName()
return name;
public void setName(String name)
this.name = name;
public Integer getAge()
return age;
public void setAge(Integer age)
this.age = age;
public String getGender()
return gender;
public void setGender(String gender)
this.gender = gender;
Java转化为JSON对象
JacksonTest
public class JacksonTest //Java对象转为JSON @Test public void test1() throws IOException //创建Person对象 Person person = new Person(); person.setName("张三"); person.setAge(21); person.setGender("男"); ObjectMapper om = new ObjectMapper(); /* writeValue(参数,obj) 参数1.: File:将对象转换为json字符串,并保存指定的文件中 Writer:将对象转换为json字符串,并将json数据填充到字符输出流中 Outputstream:将对象转换为json字符串,并将json数据填充到字节输出流中 */ /*//writeValue写到D://a.txt中 om.writeValue(new File("D://a.txt"),person);*/ //writeValue,数据关联到Writer中 // om.writeValue(new FileWriter("d://b.txt"),person); //将对象转化成json对象 String s = om.writeValueAsString(person); System.out.println(s); @Test public void test2() throws IOException //创建Person对象 Person person = new Person(); person.setName("张三"); person.setAge(21); person.setGender("男"); person.setBirthday(new Date()); ObjectMapper om = new ObjectMapper(); String s = om.writeValueAsString(person); System.out.println(s); @Test public void test3() throws IOException //创建Person对象 Person person = new Person(); person.setName("张三"); person.setAge(21); person.setGender("男"); person.setBirthday(new Date()); //创建Person对象 Person person1 = new Person(); person1.setName("张三"); person1.setAge(21); person1.setGender("男"); person1.setBirthday(new Date()); //创建Person对象 Person person2 = new Person(); person2.setName("张三"); person2.setAge(21); person2.setGender("男"); person2.setBirthday(new Date()); //创建list集合 List<Person> list = new ArrayList<Person>(); list.add(person); list.add(person1); list.add(person2); ObjectMapper om = new ObjectMapper(); String s = om.writeValueAsString(list); System.out.println(s); /** * 输出结果: * ["name":"张三","age":21,"gender":"男","birthday":"2019-08-23", * "name":"张三","age":21,"gender":"男","birthday":"2019-08-23", * "name":"张三","age":21,"gender":"男","birthday":"2019-08-23"] * */ @Test public void test4() throws IOException Map<String,Object> map=new HashMap<String, Object>(); map.put("name","李四0"); map.put("age",23); map.put("gender","男"); ObjectMapper om = new ObjectMapper(); String s = om.writeValueAsString(map); System.out.println(s); /** * 输出结果: * "gender":"男","name":"李四0","age":23 */
JSON转化为Java对象
public class JacksonTest @Test public void test5() throws IOException //初始化 String json="\\"gender\\":\\"男\\",\\"name\\":\\"李四0\\",\\"age\\":23"; ObjectMapper ob=new ObjectMapper(); //转化为Java对象 person对象 Person person = ob.readValue(json, Person.class); System.out.println(person);
案例--效验用户名是否存在
当文本输入框失去焦点,发送ajax请求,查询数据库中是否存在该用户
? 存在:提示存在
? 不存在:提示可用
1. 服务器响应的数据,在客户端使用时,要想当做json数据格式使用。有两种解决方案: 1. $.get(type):将最后一个参数type指定为"json" 2. 在服务器端设置MIME类型 response.setContentType("application/json;charset=utf-8");
效果图:
Servlet
import com.fasterxml.jackson.databind.ObjectMapper; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; import java.util.HashMap; import java.util.Map; @WebServlet("/findUserServlet") public class FindUserServlet extends HttpServlet protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException //期望服务器响应回应的格式 "userExsit":"true","msg":"用户名此用户名太受欢迎,请更换一个" // "userExsit":"false","msg":"用户名可用" Map<String, Object> map = new HashMap<String, Object>(); //设置相应格式为json response.setContentType("application/json;charset=utf-8"); //获取用户名 String username = request.getParameter("username"); System.out.println(username); //查询数据库 if ("tom".equals(username)) map.put("userExsit", true); map.put("msg", "用户名此用户名太受欢迎,请更换一个"); else map.put("userExsit", false); map.put("msg", "用户名可用"); System.out.println(map); ObjectMapper objectMapper = new ObjectMapper(); objectMapper.writeValue(response.getWriter(), map); protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException this.doPost(request, response);
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Title</title> <style> input padding: 10px; margin: 5px; </style> <script src="js/jquery-3.3.1.min.js"></script> <script> $(function () $("#username").blur(function () //获取username的值 var username = $(this).val(); //发送ajax请求 //期望服务器响应回应的格式 "userExsit":"true","msg":"用户名此用户名太受欢迎,请更换一个" // "userExsit":"false","msg":"用户名可用" $.get("findUserServlet","username":username,function (data) var span = $("#sp"); // 判断userExsit的值是否是true if (data.userExsit) //存在 span.html(data.msg) span.css("color", "red"); else // 不存在 span.html(data.msg) span.css("color", "green"); //1. //,"json"); ); ); ) </script> </head> <body> <div align="center"> <form action="" method="post"> 用户名:<input type="text" id="username" name="username" placeholder="请输入用户名"><br><span id="sp" class="span"></span><br> 密  码:<input type="password" name="password" placeholder="请输入密码"><br> <input type="submit" value="注册"> </form> </div> </body> </html>
源码地址GitHub:https://github.com/PoetryAndYou/JQuery
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