用于 JSON 数据的 Spring MVC 自定义转换器不起作用

Question

我正在创建一个测试应用程序，以在传递给控制器​​之前实现从 JSON 字符串到员工对象的转换。

以下是执行的关键步骤

• 创建 Employee.java 类：域对象
• 创建 EmployeeManagementController.java 类：用于管理员工的 Spring MVC 控制器
• 创建 EmployeeConverter.java：用于将 JSON 字符串转换为员工对象的自定义转换器。
• Creation of employee-servlet.xml : Spring Configuration file
• Creation of web.xml : The Deployment Descriptor

Employee.java

package com.bluebench.training.domain;

import org.springframework.stereotype.Component;

@Component("employee")
public class Employee {

    private PersonalDetail personal;
    private EducationDetail education;
    private WorkExperienceDetail experience;


    // Getters and Setters

}

other domain objects are also defined

EmployeeManagementController.java

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;

import com.bluebench.training.domain.Employee;

@Controller
public class EmployeeManagementController {

    @RequestMapping(value="/ems/add/employee",method=RequestMethod.POST,consumes="application/json",produces="application/json")
    public @ResponseBody int addEmployee(@RequestBody Employee emp){
        System.out.println("RAGHAVE");
        System.out.println(emp.getPersonal().getName());
        int empId = 20;
        return empId;
    }




}

EmployeeConverter.java

package com.bluebench.training.converter;

import java.io.IOException;

import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
import org.springframework.core.convert.converter.Converter;

import com.bluebench.training.domain.Employee;

public class EmployeeConverter implements Converter<String,Employee>{

    @Override
    public Employee convert(String json) {
        System.out.println("Inside convert()");
        Employee emp = null;
        try {
            emp = new ObjectMapper().readValue(json,Employee.class);
        } catch (JsonParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (JsonMappingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }           
        return emp;
    }




}

employee-servlet.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-3.0.xsd
                http://www.springframework.org/schema/context 
                http://www.springframework.org/schema/context/spring-context-3.0.xsd
                http://www.springframework.org/schema/mvc
                http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd">

                <context:component-scan base-package="com.bluebench.training"/>

                <mvc:annotation-driven  conversion-service="conversionService"/>

                <mvc:default-servlet-handler/>          

                <bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
                    <property name="mediaTypes">
                        <map>
                            <entry key="json" value="application/json" />
                            <entry key="xml" value="text/xml" />
                            <entry key="htm" value="text/html" />
                        </map>
                    </property>
                    <property name="defaultContentType" value="text/html"/>
                </bean>

                <bean id="conversionService" class="org.springframework.context.support.ConversionServiceFactoryBean">
                    <property name="converters">
                        <list>
                            <bean class="com.bluebench.training.converter.EmployeeConverter"/>
                        </list>
                    </property>
                </bean>

            </beans>

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>PROJECT_38_SpringMVCRESTFul</display-name>

  <servlet>
    <servlet-name>employee</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
  <servlet-name>employee</servlet-name>
  <url-pattern>/*</url-pattern>
  </servlet-mapping>

<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>/WEB-INF/employee-servlet.xml</param-value>
</context-param>

<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>



</web-app>

I am using Firefox RestClient to Test it.

Here is the JSON which correctly maps to the Employee object.

{"personal":{"name":"Raghave","age":33,"phoneNumber":"9594511111","address":"101, software appartment, software land , mumbai"},"education":{"qualifications":[{"insititute":"Amity University","degree":"Bachelor of Science","yearOfPassing":"2007","percentage":62.0}]},"experience":{"experience":[{"companyName":"QTBM","designation":"Programmer","years":3,"salary":12000.0},{"companyName":"Polaris","designation":"Software Developer","years":1,"salary":24000.0},{"companyName":"Ness","designation":"Senior Software Engineer","years":2,"salary":50000.0},{"companyName":"JPMC","designation":"Senior Applications Developer","years":1,"salary":120000.0}]}}

There is no Exception thrown and the controller does receive the Employee Object in the addEmployee() method. But its not via converter. The Converter is not invoked. I dont know why ? I dont want to use init binders or @Valid. I wanted to know where am i going wrong. how to make it work?

Answer 1

您已经将 Spring 使用 Converters 和 ConversionService 的一般类型转换支持与其对 HTTP 消息转换的支持混淆了，后者专门用于转换 Web 请求和响应并理解媒体类型（如您正在使用的 application/json）。HTTP 消息转换使用 HttpMessageConverter 的实例。

在这种情况下，您实际上并不需要自定义转换器。Spring 的 MappingJacksonHttpMessageConverter 用于自动执行转换。可以自动执行转换，因为大概（您还没有发布 setter，所以我在做一个有根据的猜测），Employee 中的 setter 方法与 JSON 匹配，即 setName、setAge、setPhoneNumber 等。

可以说，您拥有的代码已经可以运行了。您可以安全地删除您的自定义转换器，拥有相同的功能，并且需要维护的代码更少。如果您真的想使用自定义转换器，则需要实现 HttpMessageConverter 并在 MappingJacksonHttpMessageConverter 之前/代替 MappingJacksonHttpMessageConverter 对其进行配置。