java执行SQL语句实现查询的通用方法详解

/*    * 执行sql查询语句    */public static <T> Vector<T> executeQuery(Class<T> clazz, String sql, Object... args) {	Connection conn = null;	PreparedStatement preparedstatement = null;	ResultSet rs = null;	Vector<T> vecRs = new Vector<T>();	T obj = null;	try {		conn = JDBCTools.getConnection();		preparedstatement = conn.prepareStatement(sql);		// 通过sql语句来判断选择了那些列 		for (int i = 0; i < args.length; i++) {			preparedstatement.setObject(i + 1, args[i]);		}		// 利用sql查询获取结果集 		// 利用反射创建实体类的对象 		// 获取结果街的别名Stud_id 获取JDBC的元数据 		// 获取结果集每一列的值，结合上一步得到一个Map键值对 		// 键：列的别名 值：列的值 		// 在利用反射对实体类对象的属性赋值 		// 属性为Map的键 值为Map的值 		rs = preparedstatement.executeQuery();		// 获取元数据 		ResultSetMetaData rsmd = rs.getMetaData();		Map<String, Object> mapMetaData = new HashMap<String, Object>();		// 打印一列的列名 		while (rs.next()) {			//获取数据表中满足要求的一行数据，并放入Map中 			for (int i = 0; i < rsmd.getColumnCount(); i++) {				String columnLabel = rsmd.getColumnLabel(i + 1);				Object columnValue = rs.getObject(columnLabel);				// System.out.println(columnLabel); 				mapMetaData.put(columnLabel, columnValue);			}			//将Map中的数据通过反射初始化T类型对象 			if (mapMetaData.size() > 0) {				obj = clazz.newInstance();				for (Map.Entry<String, Object> entry : mapMetaData.entrySet()) {					String fieldkey = entry.getKey();					Object fieldvalue = entry.getValue();					// System.out.println(fieldkey + ":" + fieldvalue); 					ReflectionUtils.setFieldValue(obj, fieldkey, fieldvalue);					//通过反射赋值				}			}			//将对象装入Vector容器 			vecRs.add(obj);		}	}	catch (Exception e) {		e.printStackTrace();	}	return vecRs;}

/*    * 获取数据库的连接    */public static Connection getConnection() throws Exception {	Connection conn = null;	String driver = null;	String jdbcUrl = null;	String username = null;	String password = null;	// 获取Properties对象 	Properties properties = new Properties();	InputStream in = JDBCTools.class.getClassLoader().getResourceAsStream("jdbc.properties");	properties.load(in);	driver = properties.getProperty("driver");	jdbcUrl = properties.getProperty("jdbcUrl");	username = properties.getProperty("user");	password = properties.getProperty("password");	Class.forName(driver);	conn = DriverManager.getConnection(jdbcUrl, username, password);	return conn;}

//设置对象的属性 public static void setFieldValue(Object obj,String fieldName,Object value){	Field field=getDeclaredField(obj, fieldName);	if(field==null){		throw new IllegalArgumentException("Could not find field["+ 		    fieldName+"] on target ["+obj+"]");	}	makeAccessiable(field);	try{		field.set(obj, value);	}	catch(IllegalAccessException e){		System.out.println("不可能抛出的异常");	}}//判断field的修饰符是否是public,并据此改变field的访问权限 public static void makeAccessiable(Field field){	if(!Modifier.isPublic(field.getModifiers())){		field.setAccessible(true);	}}//获取field属性，属性有可能在父类中继承 public static Field getDeclaredField(Object obj,String fieldName){	for (Class<?> clazz=obj.getClass(); clazz!=Object.class; clazz=clazz.getSuperclass()){		try{			return clazz.getDeclaredField(fieldName);		}		catch(Exception e){		}	}	return null;}