Spring MVC将对象转换为REST服务中的JSON-Java 学习之路

我正在尝试使用Spring MVC创建一个REST服务，如果我返回一个普通的字符串，它正在工作 . 我的要求是返回Java对象的JSON字符串 . 不知道如何通过隐式转换实现这一点 .

这是我的代码：

StudentService.java

package com.spring.schoolmanagement.service;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;

import com.spring.schoolmanagement.dao.CourseDAOImpl;
import com.spring.schoolmanagement.dao.StateDAOImpl;
import com.spring.schoolmanagement.dao.StudentDAOImpl;
import com.spring.schoolmanagement.model.Student;

@Controller
@RequestMapping("/rest/student")
public class StudentService {

    @Autowired
    private CourseDAOImpl courseService;
    @Autowired
    private StudentDAOImpl studentService;
    @Autowired
    private StateDAOImpl stateService;


    @RequestMapping(value = "/{id}", method = RequestMethod.GET, headers = "Accept=*/*")
    @ResponseBody
    public Student home(@PathVariable int id) {
        return this.studentService.getById(id);
    }

    @RequestMapping(method = RequestMethod.GET, headers = "Accept=*/*")
    @ResponseBody
    public List<Student> getAll() throws Exception {
        return this.studentService.getAll();
    }

    @RequestMapping(value = "/test", method = RequestMethod.GET, headers = "Accept=*/*")
    @ResponseBody
    public String test() {
        return "Test REST Service!!!";
    }
}

Student.java

package com.spring.schoolmanagement.model;

import java.util.Date;

import javax.validation.constraints.Size;

import org.hibernate.validator.constraints.Email;
import org.hibernate.validator.constraints.NotEmpty;
import org.springframework.format.annotation.DateTimeFormat;

public class Student extends Contact{
    private int id;

    @NotEmpty
    @Size(max = 30)
    private String firstName, lastName;
    //private String lastName;

    @DateTimeFormat(pattern="MM/dd/yyyy")
    private Date DOB, DOA;
    //private Date DOA;

    @NotEmpty
    @Email
    private String email;
    private String password;
    private int courseID;
    private String courseName;

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getFirstName() {
        return firstName;
    }
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
    public String getLastName() {
        return lastName;
    }
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
    public Date getDOB() {
        return DOB;
    }
    public void setDOB(Date dOB) {
        DOB = dOB;
    }
    public Date getDOA() {
        return DOA;
    }
    public void setDOA(Date dOA) {
        DOA = dOA;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public int getCourseID() {
        return courseID;
    }
    public void setCourseID(int courseID) {
        this.courseID = courseID;
    }
    public String getCourseName() {
        return courseName;
    }
    public void setCourseName(String courseName) {
        this.courseName = courseName;
    }
}

这里 http://localhost:8080/schoolmangement/rest/student/test 网址正在返回"Test REST Service!!!"

但是， http://localhost:8080/schoolmangement/rest/student/1 URL抛出HTTP状态代码406并显示错误消息：

The resource identified by this request is only capable of generating responses with characteristics not acceptable according to the request "accept" headers.

5 回答

1
最后，我使用Jackson库和Spring MVC获得了解决方案 . 我从Journal Dev（http://www.journaldev.com/2552/spring-restful-web-service-example-with-json-jackson-and-client-program）的例子中得到了这个解决方案

所以，我所做的代码更改是：
- 在Maven中包含库 .
- 将JSON转换Servlet添加到servlet-context.xml中 .
- 将模型更改为Serializable .
我没有对我的REST服务控制器进行任何更改 . 默认情况下，它会转换为JSON .
回复于 2024-04-27T00:48:10+08:00
6

您始终可以在Web方法上方添加 @Produces("application/json") 或指定 produces="application/json" 以返回json . 然后在 Student 类的顶部，您可以从 javax.xml.bind.annotation 包中添加 @XmlRootElement .

请注意，直接返回模型类可能不是一个好主意 . 只是一个建议 .

HTH .

回复于 2024-04-27T00:48:10+08:00

Json转换应该是开箱即用的 . 为了实现这一点，您需要添加一些简单的配置：
首先将contentNegotiationManager添加到spring配置文件中 . 它负责协商响应类型：

<bean id="contentNegotiationManager"
      class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean">
    <property name="favorPathExtension" value="false" />
    <property name="favorParameter" value="true" />
    <property name="ignoreAcceptHeader" value="true" />
    <property name="useJaf" value="false" />
     <property name="defaultContentType" value="application/json" />

      <property name="mediaTypes">
         <map>
            <entry key="json" value="application/json" />
            <entry key="xml" value="application/xml" />
         </map>
      </property>
   </bean>

   <mvc:annotation-driven
      content-negotiation-manager="contentNegotiationManager" />

   <context:annotation-config />

然后在服务的类路径中添加 Jackson2 jars（jackson-databind和jackson-core） . Jackson 负责将数据序列化为JSON . Spring会自动检测这些并自动初始化 MappingJackson2HttpMessageConverter . 只有这个配置我有自动转换为JSON工作 . 如果设置 accept:application/xml 标头，所描述的配置还有一个额外的好处，即可以序列化为XML .

回复于 2024-04-27T00:48:10+08:00

0
当控制器正确注释时，Spring框架本身处理json转换 .

例如：
```
@PutMapping(produces = {"application/json"})
        @ResponseBody
        public UpdateResponse someMethod(){ //do something
return UpdateResponseInstance;
}
```
这里spring在内部将UpdateResponse对象转换为相应的json字符串并返回它 . 为了做到这一点，内部使用了Jackson library.

如果在控制器之外的任何地方需要模型对象的json表示，那么可以使用jackson提供的objectMapper . 模型应该正确注释，以便工作 .

例如：
```
ObjectMapper mapper = new ObjectMapper();
SomeModelClass someModelObject = someModelRepository.findById(idValue).get();
mapper.writeValueAsString(someModelObject);
```
回复于 2024-04-27T00:48:10+08:00

另一个简单的解决方案是在POM中添加jackson-databind依赖项 .

<dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.8.1</version>
    </dependency>

保持其余代码不变 .

回复于 2024-04-27T00:48:10+08:00

Spring MVC将对象转换为REST服务中的JSON

5 回答

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