Question

我正在使用springframework编写一个简单的休息服务，并且在尝试通过Chrome浏览器访问我的休息服务时收到以下错误消息。

错误处理请求

上下文路径：/simple_app-1.0-SNAPSHOT

Servlet路径：/

路径信息：null

查询字符串：null

堆栈跟踪

org.springframework.web.util.NestedServletException：Request   处理失败;嵌套异常是java.lang.NullPointerException

org.springframework.web.servlet.FrameworkServlet.processRequest（FrameworkServlet.java:979）

org.springframework.web.servlet.FrameworkServlet.doGet（FrameworkServlet.java:858）

javax.servlet.http.HttpServlet.service（HttpServlet.java:687）

org.springframework.web.servlet.FrameworkServlet.service（FrameworkServlet.java:843）

这是我的 pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>
    <name>SIMPLE_REST_V1</name>
    <groupId>com.rest.app</groupId>
    <artifactId>simple_app</artifactId>
    <packaging>war</packaging>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <spring.version>4.2.6.RELEASE</spring.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context-support</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-aop</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-aspects</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-beans</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-expression</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-jdbc</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-orm</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-oxm</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-tx</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-web</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc-portlet</artifactId>
            <version>${spring.version}</version>
        </dependency>

        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-swagger2</artifactId>
            <version>2.0.1</version>
        </dependency>

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>2.4.1</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.4.1.1</version>
        </dependency>

        <dependency>
            <groupId>org.codehaus.jackson</groupId>
            <artifactId>jackson-mapper-asl</artifactId>
            <version>1.9.13</version>
        </dependency>

        <dependency>
            <groupId>org.codehaus.jackson</groupId>
            <artifactId>jackson-core-asl</artifactId>
            <version>1.9.13</version>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>2.1.1</version>
                <configuration>
                    <failOnMissingWebXml>true</failOnMissingWebXml>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

的web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 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_2_5.xsd">

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

    <servlet>
        <servlet-name>RestAPI</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>/WEB-INF/context.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>RestAPI</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

</web-app>

和 context.xml

<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-4.0.xsd
                           http://www.springframework.org/schema/mvc
                           http://www.springframework.org/schema/mvc/spring-mvc-4.0.xsd
                           http://www.springframework.org/schema/context
                           http://www.springframework.org/schema/context/spring-context-4.0.xsd">

    <context:component-scan base-package="com.sumit.rest.app"/>
    <mvc:annotation-driven/>

</beans>

RESTController

@Controller
@RequestMapping(value = "/")
public class RESTController {
    private static AtomicLong counter = new AtomicLong();
    private final static String template = "Hello, %s";

    @RequestMapping(method = RequestMethod.GET, headers = "Accept=application/json")
    @ResponseBody
    public Map<String, String> get() {
        Map<String,String> map = new HashMap<>();
        map.put("value","this is the default response");
        return map;
    }


    @RequestMapping(value = "/greet", method = RequestMethod.GET, headers = "Accept=application/json", produces = MediaType.APPLICATION_JSON_VALUE)
    @ResponseBody
    public Greeting getGreeting(@RequestParam(value = "name", defaultValue = "World") String name) {
        Greeting greet =  new Greeting(counter.incrementAndGet(), String.format(template, name));
        System.out.println(greet);
        return greet;
    }
 }

最后 Greet.java

@JsonAutoDetect
public class Greeting {
    public final long id;
    public final String message;

    public Greeting(long id, String message) {
        this.id = id;
        this.message = message;
    }

    public long getId() {
        return id;
    }

    public String getMessage() {
        return message;
    }

    @Override
    public String toString() {
        return "id = "+this.id + " and name = "+this.message;
    }
}

你可以指出我错过的地方或犯错的地方吗？

我期望在浏览器上的响应是Greet类对象的json表示。

上面的代码是来自https://spring.io/guides/gs/rest-service/的示例代码，但唯一的区别是我正在尝试的是该示例的非Spring引导版本。

下面是错误

的屏幕截图

任何帮助将不胜感激！

感谢您的期待。

Answer 1

您的案例中设置了两种应用程序上下文

（这里明确说明Purpose of ContextLoaderListener – Spring MVC和here）。

简而言之如果您已在一个弹簧配置文件中配置了所有内容，那么当您使用

ContextLoaderListener

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

它会在 WEB-INF 下搜索 applicationContext.xml ，我猜你没有这个文件所以只需要删除这个声明。

如果您使用wildFly 8.1，请将其升级到较新版本。

使用@Controller注释

1 个答案: