Servlet.service（） for servlet [dispatcher] 在上下文中，路径 [/***] 抛出异常

java maven spring

2022-09-04 02:34:09

我在创建弹簧maven rest Web服务时遇到以下错误。当尝试使用在application_config.xml中定义的bean名称调用DAO类时，获取NullPointerException

SEVERE: Servlet.service() for servlet [dispatcher] in context with path [/riceAppService] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException
    at com.ganeshTrading.riceAppService.controller.UserController.getAllUsers(UserController.java:46)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:114)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:212)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:528)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1099)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:670)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1520)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1476)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:748)

这里，是我的代码

用户控制器.java

    @RestController
public class UserController {

    private JdbcUserDAO jdbcUserDAO;


    public JdbcUserDAO getJdbcUserDAO() {
        return jdbcUserDAO;
    }

    public void setJdbcUserDAO(JdbcUserDAO jdbcUserDAO) {
        this.jdbcUserDAO = jdbcUserDAO;
    }

    @RequestMapping("/")
    @ResponseBody
    public String welcome() {
        return "Welcome to RestTemplate Example.";
    }

    @RequestMapping(value="/users", method=RequestMethod.GET, produces=MediaType.APPLICATION_JSON_VALUE)
    @ResponseBody   
    public List<User> getAllUsers() {
        System.out.println("jdbcUserDAO"+jdbcUserDAO);
        List<User> userList = jdbcUserDAO.getAllUsers();
        System.out.println(userList);
        return userList;
    }

}

用户道.java

public interface UserDAO {

    public List<User> getAllUsers();
}

JdbcUserDAO.java

public class JdbcUserDAO implements UserDAO {

    DataSource dataSource;


    public void setDataSource(DataSource dataSource) {
        this.dataSource = dataSource;
    }


    @Override
    public List<User> getAllUsers() {
        String sql = "select * from customer";
        JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
        System.out.println("getJdbcTemplate() "+jdbcTemplate);
        List<User> userList = jdbcTemplate.query(sql, new UserMapper());
        return userList;
    }

}

servlet-context.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" 
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
 xsi:schemaLocation=" http://www.springframework.org/schema/beans  
 http://www.springframework.org/schema/beans/spring-beans-4.3.xsd 
 http://www.springframework.org/schema/context 
 http://www.springframework.org/schema/context/spring-context-4.3.xsd
 http://www.springframework.org/schema/mvc 
 http://www.springframework.org/schema/mvc/spring-mvc-4.3.xsd">



<context:annotation-config />
<mvc:annotation-driven />

<import resource="classpath:application_config.xml" /> 
<context:component-scan base-package="com.ganeshTrading.riceAppService" />

</beans>

application_config.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"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-4.3.xsd">


    <bean id="jdbcUserDAO" class="com.ganeshTrading.riceAppService.dao.impl.JdbcUserDAO">
        <property name="dataSource" ref="dataSource" />
    </bean>

   <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
    <property name="driverClassName" value="com.mysql.jdbc.Driver"></property>
    <property name="url" value="jdbc:mysql://localhost:3306/ganeshricetrading"></property>
    <property name="username" value="root"></property>
    <property name="password" value="sql"></property>
   </bean>    

</beans>

网.xml

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

<web-app xmlns:xsi="w3.org/2001/XMLSchema-instance" xmlns="xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="xmlns.jcp.org/xml/ns/javaee xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
      <display-name>Archetype Created Web Application</display-name>
  <servlet>
    <servlet-name>appServlet</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/servlet-context.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>appServlet</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
</web-app>

应用程序配置.java

@ComponentScan(basePackages = {"com.ganeshTrading.riceAppService"})
@Configuration
@EnableWebMvc
public class ApplicationConfiguration {

}

请告知我的代码中有什么问题。提前致谢。

答案 1

尽管您已经定义了 Bean，但尚未将其连接到类中。这会导致 a，因为字段是，这导致在调用时出现异常。要解决此问题，请在 with 中注释 setter，如：jdbcUserDAOUserControllerNullPointerExceptionjdbcUserDAOnulljdbcUserDAO.getAllUsers()jdbcUserDAOUserController@Autowired

@RestController
public class UserController {

    private JdbcUserDAO jdbcUserDAO;

    public JdbcUserDAO getJdbcUserDAO() {
        return jdbcUserDAO;
    }

    @Autowired
    public void setJdbcUserDAO(JdbcUserDAO jdbcUserDAO) {
        this.jdbcUserDAO = jdbcUserDAO;
    }

    @RequestMapping("/")
    @ResponseBody
    public String welcome() {
        return "Welcome to RestTemplate Example.";
    }

    @RequestMapping(value="/users", method=RequestMethod.GET, produces=MediaType.APPLICATION_JSON_VALUE)
    @ResponseBody   
    public List<User> getAllUsers() {
        System.out.println("jdbcUserDAO"+jdbcUserDAO);
        List<User> userList = jdbcUserDAO.getAllUsers();
        System.out.println(userList);
        return userList;
    }

}

注释告诉Spring，应该将与 setter 的参数接口匹配的 bean（在本例中为）注入到 setter 中，这会导致将字段设置为在中定义的 bean。@AutowiredJdbcUserDAOjdbcUserDAOJdbcUserDAOapplication_config.xml

您还可以简化字段并对其进行注释（删除 getter 和 setter）：UserController

@RestController
public class UserController {

    @Autowired
    private JdbcUserDAO jdbcUserDAO;

    @RequestMapping("/")
    @ResponseBody
    public String welcome() {
        return "Welcome to RestTemplate Example.";
    }

    @RequestMapping(value="/users", method=RequestMethod.GET, produces=MediaType.APPLICATION_JSON_VALUE)
    @ResponseBody   
    public List<User> getAllUsers() {
        System.out.println("jdbcUserDAO"+jdbcUserDAO);
        List<User> userList = jdbcUserDAO.getAllUsers();
        System.out.println(userList);
        return userList;
    }

}

有关详细信息，请参阅春季@Autowired指南。

看起来您也没有包含在Spring的应用程序上下文中。若要包含此 XML 文件，请将类更改为类似于以下内容：application_config.xmlApplicationConfiguration

@ComponentScan(basePackages = {"com.ganeshTrading.riceAppService"})
@Configuration
@EnableWebMvc
@ImportResource("classpath:/path/to/application_config.xml")
public class ApplicationConfiguration {

}

请注意，这是一个示例，应改用文件的实际位置。classpath:/path/to/application_config.xmlapplication_config.xml

答案 2