Java基础--JDBC-反射等

「爱情、让人受尽委屈。」 2022-07-15 12:23 188阅读 0赞

User类

package com.JDBCTest;
    
    import java.util.Date;
    
    public class User {
    
    	private Integer id;
    	private String username;
    	private String address;
    	private Date birthday;
    
    	public Integer getId() {
    		return id;
    	}
    
    	public void setId(Integer id) {
    		this.id = id;
    	}
    
    	public String getUsername() {
    		return username;
    	}
    
    	public void setUsername(String username) {
    		this.username = username;
    	}
    
    	public String getAddress() {
    		return address;
    	}
    
    	public void setAddress(String address) {
    		this.address = address;
    	}
    
    	public Date getBirthday() {
    		return birthday;
    	}
    
    	public void setBirthday(Date birthday) {
    		this.birthday = birthday;
    	}
    }

接口类

package com.JDBCTest;
    
    import java.sql.ResultSet;
    import java.sql.SQLException;
    
    @FunctionalInterface
    public interface ResultSetExtractor {
    	
    	//函数泛型
    	public  Object extractData(ResultSet rs) throws SQLException; 
    }

反射类

package com.JDBCTest;
    
    import java.lang.reflect.Method;
    import java.util.Date;
    
    public class ReflectUtil {
       
    	/**
    	 * 设置对象的参数
    	 */
    	public static void setValue(String name,Object value,Object obj){
    		try {
    			Class clz = obj.getClass();
    			String tname = value.getClass().getTypeName();
    			Method method = clz.getDeclaredMethod("set"+name, Class.forName(tname));
    			method.invoke(obj, value);
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    	}
    	
    //	public static void main(String[] args) {
    //		User user = new User();
    //		ReflectUtil.setValue("Id", "7", user);
    //		ReflectUtil.setValue("Username", "tt", user);
    //		ReflectUtil.setValue("Address", "上海", user);
    //	}
     
    }

实现类

package com.JDBCTest;
    
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.ResultSetMetaData;
    import java.sql.SQLException;
    import java.util.ArrayList;
    import java.util.LinkedList;
    import java.util.List;
    
    
    public class Session {
    
    	private static final String url = "jdbc:mysql://119.254.106.50:3309/test?useUnicode=true&characterEncoding=utf8";
    	private static final String user = "rw_all_db";
    	private static final String password = "rw_all_db";
    	
    	/**
    	 * 获取单条数据
    	 */
    	public <T>T query(String sql,ResultSetExtractor extractor){
    		try {
    			Class.forName("com.mysql.jdbc.Driver");
    			Connection connection = DriverManager.getConnection(url, user, password);
    			PreparedStatement statement = connection.prepareStatement(sql);
    			ResultSet rs = statement.executeQuery();
    			rs.next();
    			return (T)extractor.extractData(rs);
    		} catch (Exception e) {
    			return null;
    		} finally {
    			//关闭连接
    		}
    	}
    	
    	/**
    	 * 带参数获取单条数据
    	 */
    	public <T>T query(String sql,ResultSetExtractor extractor,Object...params){
    		try {
    			Class.forName("com.mysql.jdbc.Driver");
    			Connection connection = DriverManager.getConnection(url, user, password);
    			PreparedStatement statement = connection.prepareStatement(sql);
    			if(params!=null && params.length > 0){
    				for (int i = 0; i < params.length; i++) {
    					Object object = params[i];
    					statement.setObject(i+1, object);
    				}
    			}
    			ResultSet rs = statement.executeQuery();
    			rs.next();
    			return (T)extractor.extractData(rs);
    		} catch (Exception e) {
    			return null;
    		}
    	}
    	
    	
    	/**
    	 * 带参数获取多条数据
    	 */
    	public <T>List<T> queryList(String sql,ResultSetExtractor extractor,Object...params){
    		try {
    			Class.forName("com.mysql.jdbc.Driver");
    			Connection connection = DriverManager.getConnection(url, user, password);
    			PreparedStatement statement = connection.prepareStatement(sql);
    			if(params!=null && params.length > 0){
    				for (int i = 0; i < params.length; i++) {
    					Object object = params[i];
    					statement.setObject(i+1, object);
    				}
    			}
    			ResultSet rs = statement.executeQuery();
    			List<T> lists = new ArrayList<>();
    			while (rs.next()) {
    				lists.add((T)extractor.extractData(rs));
    			}
    			return lists;
    		} catch (Exception e) {
    			return null;
    		}
    	}
    	
    	
    	/**
    	 * 反射
    	 */
    	public <T>List<T> queryList(String sql,Class clz,Object...params){
    		try {
    			Class.forName("com.mysql.jdbc.Driver");
    			//获取连接对象
    			Connection connection = DriverManager.getConnection(url, user, password);
    			//执行预处理对象
    			PreparedStatement statement = connection.prepareStatement(sql);
    			//设置参数
    			if(params!=null && params.length > 0){
    				for (int i = 0; i < params.length; i++) {
    					Object object = params[i];
    					statement.setObject(i+1, object);
    				}
    			}
    			//结果集
    			ResultSet rs = statement.executeQuery();
    			//拿到获取sql语句 select ***from 这段的列明
    			ResultSetMetaData metaData = rs.getMetaData();
    			int count = metaData.getColumnCount();
    			//定义个集合存储这些列名
    			LinkedList<String> colunmNames = new LinkedList<>();
    			for (int i = 0; i < count; i++) {
    				colunmNames.add(metaData.getColumnName(i+1));//解析存储
    			}
    
    			//定义容器，装载数据
    			List<T> lists = new ArrayList<>();
    			while (rs.next()) {
    				//实例化对象
    				T obj = (T)clz.newInstance();
    				for (String string: colunmNames) {
    					//讲数据库对应的列明转换成javabean中对应的属性名，首字母转大写,因为setUsername
    					//columnToProperty()讲数据库列名转换成驼峰命名规则，create_time ---createTime
    					//create_time --columnToProperty--createTime--toUpperCaseFirst---CreateTime
    					String colunmName = string.substring(0, 1).toUpperCase() + string.substring(1);
    					//调用反射，给属性赋值
    					ReflectUtil.setValue(colunmName, rs.getObject(colunmName), obj);
    				}
    				//将数据放入集合中
    				lists.add(obj);
    			}
    
    			return lists;
    		} catch (Exception e) {
    			return null;
    		}
    	}
    	
    	public static void main(String[] args) {
    		Session session = new Session();
    		//测试一：单条数据
    //		String sql = "select id,username,address from user where id = 1";
    //		User user1 = session.query(sql, new ResultSetExtractor() {
    //			
    //			@Override
    //			public User extractData(ResultSet rs) throws SQLException {
    //				User user = new User();
    //				user.setId(rs.getInt("id"));
    //				user.setUsername(rs.getString("username"));
    //				user.setAddress(rs.getString("address"));
    //				return user;
    //			}
    //		});
    //		System.out.println(user1.getId()+"=>"+user1.getAddress()+"=>"+user1.getUsername());
    		
    		//测试二：带参数单条数据
    //		String sql = "select id,username,address from user where id = ?";
    //		User user1 = session.query(sql, new ResultSetExtractor() {
    //			
    //			@Override
    //			public User extractData(ResultSet rs) throws SQLException {
    //				User user = new User();
    //				user.setId(rs.getInt("id"));
    //				user.setUsername(rs.getString("username"));
    //				user.setAddress(rs.getString("address"));
    //				return user;
    //			}
    //		},5);
    //		System.out.println(user1.getId()+"=>"+user1.getAddress()+"=>"+user1.getUsername());
    		
    		//测试三：带参数多条数据
    		String sql = "select id,username,address from user where address = ?";
    //		List<User> list = session.queryList(sql, new ResultSetExtractor() {
    //			
    //			@Override
    //			public User extractData(ResultSet rs) throws SQLException {
    //				User user = new User();
    //				user.setId(rs.getInt("id"));
    //				user.setUsername(rs.getString("username"));
    //				user.setAddress(rs.getString("address"));
    //				return user;
    //			}
    //		},"北京");
    //		
    //		for (User user1 : list) {
    //			System.out.println(user1.getId()+"=>"+user1.getAddress()+"=>"+user1.getUsername());
    //		}
    
    		//lamad函数改写
    //		List<User> list1 = session.queryList(sql, (rs) -> {
    //				User user = new User();
    //				user.setId(rs.getInt("id"));
    //				user.setUsername(rs.getString("username"));
    //				user.setAddress(rs.getString("address"));
    //				return user;}
    //		,"北京");
    //		
    //		for (User user1 : list1) {
    //			System.out.println(user1.getId()+"=>"+user1.getAddress()+"=>"+user1.getUsername());
    //		}
    		
    		//反射测试
    		List<User> list = session.queryList(sql,User.class,"上海");
    		for (User user1 : list) {
    		System.out.println(user1.getId()+"=>"+user1.getAddress()+"=>"+user1.getUsername());
    	}
      }
    }