纯Java版本的JDBC基础操作，支持查询结果到泛型实体类的转换

闲来无事，纯手工撸了一把JDBC基础操作（从配置文件获取连接、CRUD、关闭等），基于MySQL，不依赖其它第三方库。代码如下。

---

package com.ldj.jdbc;

/*
 * 纯Java代码版本的JDBC操作
 * 支持查询结果到(泛型)实体类的映射
 * 实体类为简单的JAVA Bean，即不包含复杂的对象属性
 *
 * author: laideju [email protected]
 * version: 1.0
 * date: 2018-10-25
 * 
 * */

import java.io.InputStream;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Properties;

public class SimpleJdbcHelper {
	
	private static String driver = "";
	private static String url="";
	private static String userName="";
	private static String password="";
	
	static {
		Properties props = new Properties();
		try {
			InputStream is = SimpleJdbcHelper.class.getClassLoader().getResourceAsStream("db.properties");
			props.load(is);
			driver = props.getProperty("driver");
			url=props.getProperty("url");
			userName=props.getProperty("userName");
			password = props.getProperty("password");
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public static String getDriver() {
		return driver;
	}

	public static String getUrl() {
		return url;
	}

	public static String getUserName() {
		return userName;
	}

	public static String getPassword() {
		return password;
	}
	
	public static Connection getConnection() {
		Connection conn = null;		
		try {
			Class.forName(driver);
			conn = DriverManager.getConnection(url, userName, password);
		} catch (Exception e) {
			e.printStackTrace();
		}
		
		return conn;
	}
	
	public static void close(ResultSet rs, Statement stat, Connection conn) {
		if(rs!=null) {
			try {
				rs.close();
				rs = null;
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		
		if(stat != null) {
			try {
				stat.close();
				stat = null;
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		
		if(conn != null) {
			try {
				conn.close();
				conn = null;
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
	}
	
	/*
	 *	批量执行插入、更新、删除
	 */
	public static int batchExecute(String sql, Object[][] params) {
		int ret = -1;
		Connection conn = null;
		PreparedStatement stat = null;
		try {
			conn = getConnection();
			stat = conn.prepareStatement(sql);
			if(params!=null) {
				for (int i = 0, n = params.length; i < n; i++) {
					for(int j = 0, m = params[i].length; j < m; j++) {
						stat.setObject(j+1, params[i][j]);
					}
					stat.addBatch();
				}
			} else { // 这里如果不执行 addBatch() 方法，则执行后不会有任何结果
				stat.addBatch();
			}
			
			int[] rowNumList = stat.executeBatch();			
			if(rowNumList != null && rowNumList.length > 0) {
				ret = 0;
				for(int num : rowNumList) {
					ret += num;
				}
			}
			
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			close(null, stat, conn);
		}		
		return ret;
	}
	
	/*
	 * 单条记录的插入、删除、更新
	 */
	public static int execute(String sql, Object[] params) {
		if(params == null) {
			return batchExecute(sql, null);
		} else {
			Object[][] wrapedParams = {params};
			return batchExecute(sql, wrapedParams);
		}
	}
	
	/*
	 *	获取实体对象
	 */
	public static List queryResult(String sql, Object[] args, Class clazz){
		Connection conn = null;
		PreparedStatement stat = null;
		ResultSet rs = null;
		List list = new ArrayList();
		try {
			conn=getConnection();
			stat =conn.prepareStatement(sql);
			if(args!=null) {
				for(int i=0, n=args.length;i methodNameMap = new HashMap();
				for(Method m:methods) {
					String methodName = m.getName().toLowerCase();
					if(!methodName.startsWith("set")) {
						continue;
					}				
					int mod = m.getModifiers();
					boolean isInstancePublicSetter = Modifier.isPublic(mod) && !Modifier.isStatic(mod) && !Modifier.isAbstract(mod);
					if(isInstancePublicSetter) {
						methodNameMap.put(methodName, m);
					}
				}			
				
				while(rs.next()) {
					Object obj = clazz.newInstance();
					for(int i=1; i <= totalProps; i++) {
						Object currentColumnVal = rs.getObject(i);
						String currentColumnName = meta.getColumnName(i);
						Method m = methodNameMap.get("set"+currentColumnName);
						if(m!=null) {
							m.invoke(obj, currentColumnVal);
						}
					}
					list.add((T)obj);
				}						
				
			} else { // 异常情形：既不是单列结果，也没有指明实体类的类型
				throw new Exception("queryResult(String sql, Object[] args, Class clazz) 非单列结果且未指明clazz的值");
			}			
			
		} catch (Exception e) {
			e.printStackTrace();
		}
		return list;
	}	

	/*
	 * 获取统计函数的查询结果
	 */
	public static Number getSimpleResult(String sql, Object[] params) {
		Number ret =-1;
		Connection conn = null;
		PreparedStatement stat = null;
		ResultSet rs = null;
		try {
			conn = getConnection();
			stat = conn.prepareStatement(sql);
			if(params!=null) {
				for (int i = 0, n = params.length; i < n; i++) {
					stat.setObject(i+1, params[i]);
				}
			}
			
			rs = stat.executeQuery();
			if(rs.next()) {
				ret = (Number)rs.getObject(1);
			}
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			close(rs, stat, conn);
		}		
		return ret;
	}
	
}