一次反射的应用

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

public class JdbcGetAll {

    // 传入表名和类名和Connection对象,会将给定表中的每条数据转换成给定的类的实例.
    // 要求,表的字段的字段名和数据类型要和类的字段名和类型一一对应
    public List getAll(String tableName, String className, Connection conn) {
        
        // 从给定的类名获得类传至该变量
        Class thisClass;

        // 类的字段的数组
        Field[] thisFields;

        // 类的字段的Map,方便根据字段名获取到Field对象
        HashMap<String, Field> thisFieldsMap = new HashMap<>();

        // 类的构造器
        Constructor thisConstructor = null;

        // 表的字段名的集合
        var COLUMN_NAMEs = new ArrayList<String>();

        // 用于盛放生成的对象的数组,最终返回该对象
        var thisInstances = new ArrayList();

        try {
            thisClass = Class.forName(className);
            thisConstructor = thisClass.getConstructor();
            thisFields = thisClass.getFields();

            for (var field : thisFields) {
                thisFieldsMap.put(field.getName(), field);
            }

        } catch (ClassNotFoundException e) {
            System.out.println("No class called '" + className + "'");
            return null;
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        }

        // 获取到表的字段的sql语句
        var sql = "select COLUMN_NAME from information_schema.COLUMNS where table_name = '" + tableName + "'";

        PreparedStatement pstmt = null;
        ResultSet rs = null;
        try {
            pstmt = conn.prepareStatement(sql);
            rs = pstmt.executeQuery();
            while (rs.next()) {
                var COLUMN_NAME = rs.getString("COLUMN_NAME");
                COLUMN_NAMEs.add(COLUMN_NAME);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }

        // 获取表的数据
        sql = "select * from " + tableName;

        try {
            pstmt = conn.prepareStatement(sql);
            rs = pstmt.executeQuery();

            // 遍历所有记录,为每条记录生成一个类实例
            while (rs.next()) {
                try {
                    // 从类的构造器创建新的实例
                    var thisInstance = thisConstructor.newInstance();

                    // 遍历所有表的字段
                    for (var COLUMN_NAME : COLUMN_NAMEs) {

                        // 获取到表的字段名对应的对象字段
                        var field = thisFieldsMap.get(COLUMN_NAME);

                        // 获取到该条记录该条字段的值
                        var o = rs.getObject(COLUMN_NAME);

                        // 为对象的字段设置值
                        field.set(thisInstance, o);
                    }
                    thisInstances.add(thisInstance);
                } catch (InstantiationException e) {
                    e.printStackTrace();
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                } catch (InvocationTargetException e) {
                    e.printStackTrace();
                }
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            JdbcUitl.close(pstmt, conn);
        }

        return thisInstances;
    }

    public static void main(String[] args) {
        Connection conn = JdbcUitl.getConnection("address", 3306, "dbName", "root", "password");
        var jdbcGetAll = new JdbcGetAll();
        List res = jdbcGetAll.getAll("teacher", "Teacher", conn);
        System.out.println("结果集中共含有" + res.size() + "个元素: {");
        for (var re : res) {
            System.out.println("    " + re);
        }
        System.out.println("}");
    }
}

JdbcUtil类的代码

import java.sql.*;

public class JdbcUitl {
    public static Connection getConnection(String address,int port,String dbName,String userName,String passWord){
        Connection conn = null;
        try {
            conn = DriverManager.getConnection("jdbc:mysql://" + address + ":" + port + "/" + dbName,userName,passWord);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return conn;
    }

    public static void close(PreparedStatement pstmt,Connection conn){
        if(pstmt!=null){
            try {
                pstmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if(conn!=null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}