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); } }html
<!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