java執(zhí)行SQL語句實(shí)現(xiàn)查詢的通用方法詳解

/* 
   * 執(zhí)行sql查詢語句 
   */
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);
		// 通過sql語句來判斷選擇了那些列 
		for (int i = 0; i < args.length; i++) {
			preparedstatement.setObject(i + 1, args[i]);
		}
		// 利用sql查詢獲取結(jié)果集 
		// 利用反射創(chuàng)建實(shí)體類的對象 
		// 獲取結(jié)果街的別名Stud_id 獲取JDBC的元數(shù)據(jù) 
		// 獲取結(jié)果集每一列的值，結(jié)合上一步得到一個Map鍵值對 
		// 鍵：列的別名 值：列的值 
		// 在利用反射對實(shí)體類對象的屬性賦值 
		// 屬性為Map的鍵 值為Map的值 
		rs = preparedstatement.executeQuery();
		// 獲取元數(shù)據(jù) 
		ResultSetMetaData rsmd = rs.getMetaData();
		Map<String, Object> mapMetaData = new HashMap<String, Object>();
		// 打印一列的列名 
		while (rs.next()) {
			//獲取數(shù)據(jù)表中滿足要求的一行數(shù)據(jù)，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);
			}
			//將Map中的數(shù)據(jù)通過反射初始化T類型對象 
			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);
					//通過反射賦值
				}
			}
			//將對象裝入Vector容器 
			vecRs.add(obj);
		}
	}
	catch (Exception e) {
		e.printStackTrace();
	}
	return vecRs;
}

/* 
   * 獲取數(shù)據(jù)庫的連接 
   */
public static Connection getConnection() throws Exception {
	Connection conn = null;
	String driver = null;
	String jdbcUrl = null;
	String username = null;
	String password = null;
	// 獲取Properties對象 
	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;
}

//設(shè)置對象的屬性 
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("不可能拋出的異常");
	}
}
//判斷field的修飾符是否是public,并據(jù)此改變field的訪問權(quán)限 
public static void makeAccessiable(Field field){
	if(!Modifier.isPublic(field.getModifiers())){
		field.setAccessible(true);
	}
}
//獲取field屬性，屬性有可能在父類中繼承 
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;
}