package com.imooc.dao;
import com.imooc.domain.Student;
import org.junit.Test;
import java.util.List;
public class StudentDAOImplTest {
@Test
public void testQuery() {
StudentDAO studentDAO = new StudentDAOImpl();
List<Student> students = studentDAO.query();
for (Student student : students){
System.out.println("id:" + student.getId()
+ ",name:" + student.getName()
+ ",age:" + student.getAge());
}
}
}
package com.imooc.dao;
import com.imooc.domain.Student;
import java.util.List;
/*
StudengDAO访问接口
*/
public interface StudentDAO {
/*
查询所有学生
*/
public List<Student> query();
}
package com.imooc.dao;
import com.imooc.domain.Student;
import com.imooc.util.JDBCUtil;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;
/*
StudentDAO访问接口实现类
*/
public class StudentDAOImpl implements StudentDAO{
@Override
public List<Student> query() {
List<Student> students = new ArrayList<Student> ();
Connection connection = null;
PreparedStatement preparedStatement = null;
ResultSet resultSet = null;
String sql="select * from student";
try {
connection = JDBCUtil.getConnection();
preparedStatement = connection.prepareStatement(sql);
resultSet = preparedStatement.executeQuery();
Student student = null;
while (resultSet.next()) {
int id = resultSet.getInt("id");
String name = resultSet.getString("name");
int age = resultSet.getInt("age");
student = new Student();
student.setId(id);
student.setName(name);
student.setAge(age);
students.add(student);
}
} catch (Exception e) {
e.printStackTrace();
}finally {
JDBCUtil.release(resultSet,preparedStatement,connection);
}
return null;
}
}
java.lang.NullPointerException at com.imooc.dao.StudentDAOImplTest.testQuery(StudentDAOImplTest.java:14)
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:47)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.execution.junit.IdeaTestRunner$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)
报错的是第一段代码的for循环，怀疑是赋值没赋进去，有没有大佬帮我看一下
