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报了空指针异常，是JdbcTemplate的空指针

来源：3-9 持久层实现——SelectionDAO

litter_

2019-07-26 22:02:18

XML配置

<?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:aop="http://www.springframework.org/schema/aop"
       xmlns:tx="http://www.springframework.org/schema/tx"
       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/aop
    http://www.springframework.org/schema/aop/spring-aop.xsd
    http://www.springframework.org/schema/tx
    http://www.springframework.org/schema/tx/spring-tx.xsd">

    <context:component-scan base-package="com.imooc.sc.dao.impl"/>

    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/selection_course?useUnicode=true&amp;characterEncoding=utf-8"/>
        <property name="username" value="root"/>
        <property name="password" value="1234"/>
    </bean>
    <bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
        <property name="dataSource" ref="dataSource"/>
    </bean>

</beans>

这是java的Dao层三个类的方法

@Component
public class CourseDaolmpl implements CourseDao {

   @Resource(name = "jdbcTemplate")
   private JdbcTemplate jdbcTemplate;

   public void insert(Course course) {
       String sql = "insert course(name,score) values(?,?)";
       jdbcTemplate.update(sql, course.getName(), course.getScore());
   }

   public void update(Course course) {
       String sql = "UPDATE course set name=?,score=?WHERE id=?";
       jdbcTemplate.update(sql, course.getName(), course.getScore(), course.getId());
   }

   public void delete(int id) {
       String sql = "DELETE FROM course WHERE id = ?";
       jdbcTemplate.update(sql, id);
   }

   public Course select(int id) {
       String sql = "SELECT * FROM course WHERE id=?";
       Course course = jdbcTemplate.queryForObject(sql,new CourseRowMapper(),id);
       return course;

   }

   public List<Course> selectAll() {
       String sql = "SELECT * FROM course";
       return jdbcTemplate.query(sql, new CourseRowMapper());
   }

   private class CourseRowMapper implements RowMapper<Course> {

       public Course mapRow(ResultSet resultSet, int i) throws SQLException {
           Course course = new Course();
           course.setId(resultSet.getInt("id"));
           course.setName(resultSet.getString("name"));
           course.setScore(resultSet.getInt("score"));
           return course;
       }
   }

}

@Component
public class SelecttionDaolmpl implements SelectionDao {

   @Resource(name = "jdbcTemplate")
   private JdbcTemplate jdbcTemplate;

   public void insert(List<Selection> seles) {
       String sql = "INSERT selection values(?,?,?,?)";
       List<Object[]> list = new ArrayList<Object[]>();
       for (Selection sel:seles
            ) {
           Object[] args = new Object[4];
           args[0] = sel.getSid();
           args[1] = sel.getCid();
           args[2] = sel.getSelTime();
           args[3] = sel.getScore();
           list.add(args);
       }
       jdbcTemplate.batchUpdate(sql, list);

   }

   public void delete(int sid, int cid) {
       String sql = "delete from selection where sid=? and cid=?";
       jdbcTemplate.update(sql, sid, cid);
   }

   public List<Map<String, Object>> selectByStudent(int sid) {
       String sql = "SELECT s.`name` AS sname,c.`name` AS cname,se.* FROM student AS s LEFT JOIN selection AS se ON s.id=se.student INNER JOIN course AS c ON se.course = c.id WHERE s.id = ?;";

       return jdbcTemplate.queryForList(sql, sid);
   }

   public List<Map<String, Object>> selectByCourse(int cid) {
       String sql = "SELECT s.`name` AS sname,c.`name` AS cname,se.* FROM student AS s LEFT JOIN selection AS se ON s.id=se.student INNER JOIN course AS c ON se.course = c.id WHERE c.id = ?;";

       return jdbcTemplate.queryForList(sql, cid);
   }
}


@Component
public class StudentDaolmpl implements StudentDao {

   @Resource(name = "jdbcTemplate")
   private JdbcTemplate jdbcTemplate;

   public void insert(Student student) {

   }

   public void update(Student student) {
       String sql = "UPDATE student set name=?,sex=?,born=? WHERE id=?";
       jdbcTemplate.update(sql, student.getName(), student.getSex(), student.getBorn(), student.getId());
   }

   public void delete(int id) {
       String sql = "DELETE FROM student WHERE id = ?";
       jdbcTemplate.update(sql, id);
   }

   public Student select(int id) {
       String sql = "SELECT * FROM student WHERE id=?";
       return jdbcTemplate.queryForObject(sql, new StudentRowMapper(), id);
   }

   public List<Student> selectAll() {
       String sql = "SELECT * FROM student";
       return jdbcTemplate.query(sql,new StudentRowMapper());
   }

   private class StudentRowMapper implements RowMapper<Student> {

       public Student mapRow(ResultSet resultSet, int i) throws SQLException {
           Student student = new Student();
           student.setId(resultSet.getInt("id"));
           student.setName(resultSet.getString("name"));
           student.setSex(resultSet.getString("sex"));
           student.setBorn(resultSet.getDate("born"));
           return student;
       }
   }
}

这是测试类

public class DaoTest {

    private CourseDao courseDao = new CourseDaolmpl();


    @Test
    public void demo1(){
        Course course = courseDao.select(1003);
        System.out.println(course);
    }

}

这是异常信息：

"C:\Program Files\Java\jdk1.8.0_201\bin\java.exe" -ea -Didea.test.cyclic.buffer.size=1048576 "-javaagent:D:\Program Files\IntelliJ IDEA 2019.1.3\lib\idea_rt.jar=15915:D:\Program Files\IntelliJ IDEA 2019.1.3\bin" -Dfile.encoding=UTF-8 -classpath "D:\Program Files\IntelliJ IDEA 2019.1.3\lib\idea_rt.jar;D:\Program Files\IntelliJ IDEA 2019.1.3\plugins\junit\lib\junit-rt.jar;D:\Program Files\IntelliJ IDEA 2019.1.3\plugins\junit\lib\junit5-rt.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\rt.jar;D:\maven\sc\target\test-classes;D:\maven\sc\target\classes;C:\Users\adobe\.m2\repository\mysql\mysql-connector-java\5.1.41\mysql-connector-java-5.1.41.jar;C:\Users\adobe\.m2\repository\org\springframework\spring-aop\5.1.8.RELEASE\spring-aop-5.1.8.RELEASE.jar;C:\Users\adobe\.m2\repository\org\springframework\spring-beans\5.1.8.RELEASE\spring-beans-5.1.8.RELEASE.jar;C:\Users\adobe\.m2\repository\org\springframework\spring-expression\5.1.8.RELEASE\spring-expression-5.1.8.RELEASE.jar;C:\Users\adobe\.m2\repository\org\springframework\spring-context\5.1.8.RELEASE\spring-context-5.1.8.RELEASE.jar;C:\Users\adobe\.m2\repository\org\springframework\spring-core\5.1.8.RELEASE\spring-core-5.1.8.RELEASE.jar;C:\Users\adobe\.m2\repository\org\springframework\spring-jcl\5.1.8.RELEASE\spring-jcl-5.1.8.RELEASE.jar;C:\Users\adobe\.m2\repository\org\springframework\spring-jdbc\5.1.8.RELEASE\spring-jdbc-5.1.8.RELEASE.jar;C:\Users\adobe\.m2\repository\org\springframework\spring-tx\5.1.8.RELEASE\spring-tx-5.1.8.RELEASE.jar;C:\Users\adobe\.m2\repository\junit\junit\4.12\junit-4.12.jar;C:\Users\adobe\.m2\repository\org\hamcrest\hamcrest-core\1.3\hamcrest-core-1.3.jar" com.intellij.rt.execution.junit.JUnitStarter -ideVersion5 -junit4 com.imooc.sc.test.DaoTest,demo1

java.lang.NullPointerException
	at com.imooc.sc.dao.impl.CourseDaolmpl.select(CourseDaolmpl.java:38)
	at com.imooc.sc.test.DaoTest.demo1(DaoTest.java:18)
	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.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)


Process finished with exit code -1

这是pom.xml依赖文件

<?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:aop="http://www.springframework.org/schema/aop"
       xmlns:tx="http://www.springframework.org/schema/tx"
       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/aop
    http://www.springframework.org/schema/aop/spring-aop.xsd
    http://www.springframework.org/schema/tx
    http://www.springframework.org/schema/tx/spring-tx.xsd">

    <context:component-scan base-package="com.imooc.sc.dao.impl"/>

    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/selection_course?useUnicode=true&amp;characterEncoding=utf-8"/>
        <property name="username" value="root"/>
        <property name="password" value="1234"/>
    </bean>
    <bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
        <property name="dataSource" ref="dataSource"/>
    </bean>

</beans>


写回答

1回答

好帮手慕阿莹

2019-07-27

已采纳

1、首先，必须是交给spring管理的类才可以用注解注入交给spring管理的jdbcTemplate。

2、同学可能会说，我不是在CourseDaoImpl上写注解@Repository交给spring管理了吗？

是的，是交给spring管理了，但是，同学在测试类中并不是在spring中找的交给spring管理的这个对象，而是新new了一个对象，新new 的这个对象不是spring中的呦。

解决办法：

1、我们要在Test中获取spring中的CourseDaoImpl。

    1）为了好获取对象，我们给注解加上一个value值

http://img.mukewang.com/climg/5d3bd6710001113605970146.jpg

 2）和获取jdbcTemplate一样，获取 一下这个对象。

http://img.mukewang.com/climg/5d3bd6960001017510800224.jpg

3）然后用这个对象去调用方法就可以了

http://img.mukewang.com/climg/5d3bd6c700013a4604650103.jpg


如果我的回答解决了你的疑惑，请采纳！祝学习愉快！


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