叫我g少
2019-11-08 17:49
package com.imooc.dao; import com.imooc.domain.Student; import com.imooc.util.JDBCUtil; import java.io.IOException; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; 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 id , name , age from student"; try { connection = JDBCUtil.getConnection(); preparedStatement = connection.prepareStatement(sql); resultSet = preparedStatement.executeQuery(); //迭代resultSet while (resultSet.next()){ int id = resultSet.getInt("id"); String name = resultSet.getString("name"); int age = resultSet.getInt("age"); Student student = new Student(); student.setId(id); student.setAge(age); student.setName(name); students.add(student); } } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (SQLException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); }finally { JDBCUtil.release(resultSet,preparedStatement,connection); } return null; } }
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()); } } }
你这个查询方法返回的是null,不是tudents,所以空指针
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