Question

我的目标是Spring 4.2。因此，在阅读reference documentation的某些页面后，我开发了this application。

此应用程序只有一种方法。此方法应该能够返回非常简单的java对象的JSON表示。（部署应用程序后，您可以通过以下URL调用该方法：http://localhost:8080/srm/test）

相反，我收到以下错误。（ srm 是应用的上下文根目录）

HTTP ERROR 500

Problem accessing /srm/test. Reason:

    Circular view path [test]: would dispatch back to the current handler URL [/srm/test] again. Check your ViewResolver setup! (Hint: This may be the result of an unspecified view, due to default view name generation.)
Caused by:

javax.servlet.ServletException: Circular view path [test]: would dispatch back to the current handler URL [/srm/test] again. Check your ViewResolver setup! (Hint: This may be the result of an unspecified view, due to default view name generation.)
    at org.springframework.web.servlet.view.InternalResourceView.prepareForRendering(InternalResourceView.java:205)
    at org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:145)
    at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1243)
    at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1027)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:971)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:969)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:860)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:707)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:845)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:401)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:766)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:450)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
    at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:928)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:549)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:212)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:410)
    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)

我搜索并发现Spring为我的控制器方法分配了一个默认查看器。我不确定视图是什么，但在搜索之后，我有点理解 ContentNegotiatingViewResolver 对我来说是正确的。但在阅读完之后，我猜测我必须为我方法的 @RequestMapping 指定生成属性，或者为发送的内容指定接受标头从我的浏览器到我的应用程序的HTTP请求。但这一切都没有成功！

我在这里尝试做的就是能够从Spring管理的RESTful应用程序返回序列化为JSON对象的对象。我现在不想使用Spring Boot。

这是我的档案。的web.xml

<?xml version="1.0" encoding="UTF-8"?>

<web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
    <servlet>
        <servlet-name>MyAPI</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>MyAPI</servlet-name>
        <url-pattern>/*</url-pattern>
    </servlet-mapping>
</web-app>

MyAPI-servlet.xml中

<?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"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd">
    <context:component-scan base-package="com.jarmy.lab.spring.rest" />
</beans>

RESTful控制器

package com.jarmy.lab.spring.rest;

import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class MyAPI {

    @RequestMapping(value = "/test", produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
    public MyUser hello() {
        MyUser user = new MyUser();
        user.setName("Abbas");
        user.setId(12);
        return user;
    }
}

作为响应返回的示例DTO（采用JSON格式）

package com.jarmy.lab.spring.rest;

public class MyUser {
    private String name;
    private long id;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }
}

Answer 1

首先，通过向MyAPI-servlet.xml添加以下代码来启用基于注释的MVC：

<mvc:annotation-driven />

所以，你的MyAPI-servlet-xml看起来像这样：

<?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.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd 
        http://www.springframework.org/schema/mvc 
        http://www.springframework.org/schema/mvc/spring-mvc.xsd">
    <mvc:annotation-driven/>
    <context:component-scan base-package="com.jarmy.lab.spring.rest"/>
</beans>

然后添加jackson-databind依赖项：

<dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.4.0</version>
</dependency>

添加此项将注册{J}转换为JSON的MappingJackson2HttpMessageConverter。另外，删除当前的jackson mapper依赖项。

如何通过RESTful spring应用程序返回对象的JSON表示？

1 个答案: