Question

我有一个基于spring MVC框架的简单库项目。我将添加一个新作者到我的作者表，但我得到NullPointerException。我在下面提供了与此功能相关的添加类。任何人都可以说出了什么问题？

@Controller
public class AuthorController {

@RequestMapping("/addAuthor")
protected ModelAndView addAuthor() throws Exception {
    ModelAndView model = new ModelAndView("addAuthor");
    return model;
}

@RequestMapping("/addAuthorExecution")
protected ModelAndView addAuthorExecution(
        @RequestParam("authorName") String authorName) throws Exception {
    ApplicationContext cnx = new ClassPathXmlApplicationContext("spring.xml");
    AuthorService authorService = (AuthorService) cnx.getBean("authorService");
    authorService.addAuthor(authorName);
    ModelAndView model = new ModelAndView("adminFunctionsPage");
    model.addObject("successMsg", "Your request has been processed Successfully.");
    return model;
}
}

服务类：

public class AuthorService {
@Autowired
Author author;
@Autowired
AuthorDAO authorDAO;

public void addAuthor(String authorName) throws ClassNotFoundException,
        SQLException {
    AuthorDAO authorDAO = new AuthorDAO();
    authorDAO.addAuthor(authorName);
}
}

DAO课程：

public class AuthorDAO extends JdbcDaoSupport {

public void addAuthor(String authorName) {
    String sql = "insert into tbl_author (authorName) values (?)";
    this.getJdbcTemplate().update(sql, new Object[] { authorName });
}


private static final class AuthorMapper implements RowMapper<Author> {
    @Autowired
    Author author;

    @Override
    public Author mapRow(ResultSet rs, int rowNum) throws SQLException {
        author.setAuthorId(rs.getInt("authorId"));
        author.setAuthorName(rs.getString("authorName"));
        return author;
    }

}
}

模特课程：

public class Author {
int authorId;
String authorName;

public int getAuthorId() {
    return authorId;
}

public void setAuthorId(int authorId) {
    this.authorId = authorId;
}

public String getAuthorName() {
    return authorName;
}

public void setAuthorName(String authorName) {
    this.authorName = authorName;
}

}

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"
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">

<context:annotation-config/>
<context:component-scan base-package="com.hojat.LibSpringMVCProject.DAO" />
<context:component-scan base-package="com.hojat.LibSpringMVCProject.Service" />

<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
    <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
    <property name="url" value="jdbc:mysql://localhost/library"/>
    <property name="username" value="root"/>
    <property name="password" value="1234"/>
</bean>

<bean id="author" class="com.hojat.LibSpringMVCProject.model.Author"/>


<bean id="authorDAO" class="com.hojat.LibSpringMVCProject.DAO.AuthorDAO" >
    <property name="dataSource" ref="dataSource"/>
</bean>


<bean id="authorService" class="com.hojat.LibSpringMVCProject.service.AuthorService"/>

错误：

    'INFO: Loaded JDBC driver: com.mysql.jdbc.Driver
Feb 24, 2015 1:16:11 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [spring-dispatcher] in context with path [/LibrarySpringMVCProject] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException
    at com.hojat.LibSpringMVCProject.DAO.AuthorDAO.addAuthor(AuthorDAO.java:32)
    at com.hojat.LibSpringMVCProject.service.AuthorService.addAuthor(AuthorService.java:40)
    at com.hojat.LibSpringMVCProject.controller.AuthorController.addAuthorExecution(AuthorController.java:46)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:137)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:777)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:706)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:943)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:857)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:618)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:537)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1085)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:658)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:146)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:277)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)'

Answer 1

你好，你可以尝试

<property name="url" value="jdbc:mysql://localhost:3306/library"/>

而不是

<property name="url" value="jdbc:mysql://localhost/library"/>

这将是问题。

Answer 2

几个错误

您正在自动装配POJO实体类Auther。这是错误的。
希望您@Service

AuthorService

您正在AuthorDAO方法中创建addAuthor的对象。您应该注意，AutherDAO不应该手动构建，因为该类autowired中有AutherDAO.AuthorMapper个对象可用。通过手动构建它们，这些自动布线将不会连接到对象。

如果我完全重写了你的服务类，那就是这样的。

    @Service
    public class AuthorService {

        @Autowired
        AuthorDAO authorDAO;

        public void addAuthor(String authorName) throws Exception {
           authorDAO.addAuthor(authorName);
        }
    }

我在Spring MVC项目中得到NullPointerException？

2 个答案: