使用QueryRunner连接数据库获取数据为null

存数据的类（如：Student类）要有正确的setter方法（set+对应列名）。
如：

		QueryRunner queryRunner=new QueryRunner(Demo3.comboPooledDataSource);
        String sql = "SELECT * FROM S";
        try {
    
    
            List<Student> list=(List) queryRunner.query(sql,new BeanListHandler(Student.class));
            for(Student student:list)
                System.out.println(student);
        } catch (SQLException e) {
    
    
            e.printStackTrace();
        }

public class Student {
    
    
    String sclass;
    String no;
    String sname;
    String ssex;
    int sage;
    String Sdept;
	
    public void setSclass(String sclass) {
    
    
        this.sclass = sclass;
    }
	//属性名可以跟数据库的列名不一样，但set方法名一定要是set+对应列名
    public void setSno(String sno) {
    
    
        this.no = sno;
    }

    public void setSname(String sname) {
    
    
        this.sname = sname;
    }

    public void setSsex(String ssex) {
    
    
        this.ssex = ssex;
    }

    public void setSage(int sage) {
    
    
        this.sage = sage;
    }

    public void setSdept(String sdept) {
    
    
        Sdept = sdept;
    }

    @Override
    public String toString(){
    
    
        return sclass+" "+sno+" "+sname+" "+ssex+" "+sage+" "+Sdept;
    }
}