Question

我正在尝试习惯Spring项目中的Mybatis。

我将所有xml文件设置为创建datasource，sqlsession，sqlsessiontemplate的bean，并且它永远不会生成错误。

所以这次，我尝试将一些基本信息插入到只有id和密码列的用户表中。

所以这是我下面的代码。

具有Sqlsessiontemplate对象和一些相关方法的AbstactDao.class。

public class AbstractDAO {
    protected Log log = LogFactory.getLog(AbstractDAO.class);

    @Autowired
    private SqlSessionTemplate sqlSession;

    protected void printQueryId(String queryId) {
        if(log.isDebugEnabled()){
            log.debug("\t QueryId  \t:  " + queryId);
        }
    }

    public Object insert(String queryId, Object params){
        printQueryId(queryId);
        return sqlSession.insert(queryId, params);
    }

    public Object update(String queryId, Object params){
        printQueryId(queryId);
        return sqlSession.update(queryId, params);
    }

    public Object delete(String queryId, Object params){
        printQueryId(queryId);
        return sqlSession.delete(queryId, params);
    }

    public Object selectOne(String queryId){
        printQueryId(queryId);
        return sqlSession.selectOne(queryId);
    }

    public Object selectOne(String queryId, Object params){
        printQueryId(queryId);
        return sqlSession.selectOne(queryId, params);
    }

    @SuppressWarnings("rawtypes")
    public List selectList(String queryId){
        printQueryId(queryId);
        return sqlSession.selectList(queryId);
    }

    @SuppressWarnings("rawtypes")
    public List selectList(String queryId, Object params){
        printQueryId(queryId);
        return sqlSession.selectList(queryId,params);
    }
}

用户类。此类中的信息将插入数据库

public class User {

private String id;
private String pw;

public String getId() {
    return id;
}
public void setId(String id) {
    this.id = id;
}
public String getPw() {
    return pw;
}
public void setPw(String pw) {
    this.pw = pw;
}

}

mapper.xml

   <?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">


    <mapper namespace='bbs'>


    <insert id="insertuser"  parameterType="com.min.test.User">
    insert into user (id,pw) values(#{id}, #{pw})
    </insert>

    </mapper>

此代码用于在main方法中执行insert命令。

User user = new User();
    user.setId("zz");
    user.setPw("dkdkdk");

    AbstractDAO dao = new AbstractDAO();
    dao.insert("bbs.insertuser", user);

错误讯息。

Servlet.service() for servlet [appServlet] in context with path [/practice] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException
    at com.min.test.AbstractDAO.insert(AbstractDAO.java:31)
    at com.min.test.HomeController.home(HomeController.java:42)
    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.invoke(InvocableHandlerMethod.java:213)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:126)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:96)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:617)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:578)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:923)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:852)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:778)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:218)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:962)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:445)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1115)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
    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

您实例化AbstractDAO dao = new AbstractDAO();，因此永远不会分配SqlSessionTemplate sqlSession。

相反，它应标记为@Repository，您应该通过@Autowired获取它，而不是手动创建实例。

BTW：抽象类不被实例化。而是定义通用T类型并为每个实体创建不同的dao实例，例如UserDao扩展了AbstractDao并使用UserDao与User。

一起工作

在Spring项目中使用Mybatis时出错

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