通用的查询方法

package exercise;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.HashMap;
import java.util.Map;

import com.mysql.jdbc.ResultSetMetaData;

public class TestJdbc {
    public static void main(String[] args) {
        
        String sql="select Flow_ID FlowID,Type,ID_Card IDCard,Exam_Card ExamCard"+"Student_Name StudentName,Location,Grade from examstudent where Flow_Id=?";
        Student stu= get(Student.class,sql,1);
        System.out.println(stu);
        
        
        //sql=" select FlowID,Type,IDCard,ExamCard"+"StudentName,Location,Grade from examstudent where FlowId=?";
    }
    public static <T> T get(Class<T> clazz, String sql,Object...args){
        T entity=null;
        Student stu=null;
        Connection connection=null;
        PreparedStatement preparedStatement=null;
        ResultSet rs=null;
        try {
        
            Class.forName("com.mysql.jdbc.Driver");
             connection=DriverManager.getConnection//
                    ("jdbc:mysql://localhost:3306/test", "root", "123456");
            
             preparedStatement=connection.prepareStatement(sql);
             for(int i=0;i<args.length;i++){
                 preparedStatement.setObject(i+1, args[i]);
             }
            rs= preparedStatement.executeQuery();
            //创建一个Map对象 键：列的别名 值：列的值
            Map<String, Object> values=new HashMap<String,Object>();

            //得到ResultSetMetaData对象
            ResultSetMetaData rsmd=(ResultSetMetaData) rs.getMetaData();
            //处理结果集，填充map对象
            while(rs.next()){
                for(int i=0;i<rsmd.getColumnCount();i++){
                    String columnLabel=rsmd.getColumnLabel(i+1);
                    //为键和值 赋值，并放在values里面
                    Object columnValues=rs.getObject(columnLabel);
                    values.put(columnLabel, columnValues);
                }
            }
            //遍历 Map 对象, 利用反射为 Class 对象的对应的属性赋值.
            if(values.size()>0){
                entity=clazz.newInstance();
            
            for(Map.Entry<String, Object> entry: values.entrySet()){
                String FieldName=entry.getKey();
                Object FieldValues=entry.getValue();
                ReflectionUtils.setFieldValue(entity, FieldName, FieldValues);
            }
        }
            System.out.println(entity);
        
        if(rs.next()){
            entity=(T) clazz.newInstance();
            
            stu.setFlowID(rs.getInt(1));
            stu.setType(rs.getString(2));
            stu.setIDCard(rs.getString(3));
            stu.setExamCard(rs.getString(4));
            stu.setStudentName(rs.getString(5));
            stu.setLocation(rs.getString(6));
            stu.setGrade(rs.getInt(7));
        }
    }
        
    catch (Exception e) {
            
            e.printStackTrace();
        }finally{
            if(preparedStatement!=null){
                try {
                    preparedStatement.close();
                } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }finally{
                    if(connection!=null){
                        try {
                            connection.close();
                        } catch (SQLException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                    }
                }
            }
    }
        return entity;
        
    }
}