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;
}