Java中的基本数据类型转换

如果想要做ORM,将数据映射为对象,则基本的数据类型转换是必要的功能,而Java似乎未提供该功能,只有自己下手来完成该功能.

完成该功能的目标如下:

1: 提供基本的数据转换

2: 考虑转换的性能.

下面是我的具体实现:

1: 接口:

public static <T> T Cast(Class<T> t, Object value)

2: 依赖:需要依赖与获得数据默认值,因为在很多情况下,如果要转换的数据为null,调用者期望的是返回默认值.

系统自动提供的默认值不能满足我们的需求,例如int的默认值为0,但是在sql查询中,如果查询失败,我们期望的是小于0的值,例如Select Count(1) from table1这样的操作.

3: 实现:

/**
     * 类型转换
     * @param t
     * @param value
     * @return
     */
    @SuppressWarnings("unchecked")
	public static <T> T Cast(Class<T> t, Object value) {
    	if (value == null) {
    		return GetDefault(t);
    	}
		if (t == Object.class) {
			return (T)value;
		}

		try
		{
			return Cast_i(t, value);
		} catch(Exception ex) {
			ex.printStackTrace();
    		return GetDefault(t);
		}
    }

    private static String GetStr(Class<?> t, Object value) {
    	if (value == null) {
    		return "";
    	}
    	if (t == String.class){
			return (String)value;
		}else {
			return value.toString();
		}
    }

	@SuppressWarnings("unchecked")
	private static <T> T Cast_i(Class<T> t, Object value) {
    	Class<?> objClass = value.getClass();
		if (t == String.class) {
			return (T)GetStr(objClass, value);
		}
		if (t == int.class) {
			if (objClass == int.class) {
				return (T)value;
			}
			String text = GetStr(objClass, value);
			Object ret = Integer.parseInt(text);
			return (T)ret;
		}
		if (t == Integer.class) {
			if (objClass == Integer.class) {
				return (T)value;
			}
			if (objClass == int.class) {
				return (T)value;
			}
			String text = GetStr(objClass, value);
			Object ret = Integer.parseInt(text);
			return (T)ret;
		}
		if (t == short.class) {
			if (objClass == int.class) {
				return (T)value;
			}
			String text = GetStr(objClass, value);
			Object ret = Short.parseShort(text);
			return (T)ret;
		}
		if (t == boolean.class || t == Boolean.class) {
			if (objClass == int.class) {
				Object ret = (int)value >= 1? true:false;
				return (T)ret;
			}
			if (objClass == Integer.class) {
				Object ret = (Integer)value >= 1? true:false;
				return (T)ret;
			}
			String text = GetStr(objClass, value);
			Object ret = Integer.parseInt(text);
			ret = (int)ret >= 1? true:false;
			return (T)ret;
		}
		if (t == long.class) {
			if (objClass == long.class) {
				return (T)value;
			}
			String text = GetStr(objClass, value);
			Object ret = Long.parseLong(text);
			return (T)ret;
		}
		if (t == byte.class) {
			if (objClass == byte.class) {
				return (T)value;
			}
			String text = GetStr(objClass, value);
			Object ret = Byte.parseByte(text);
			return (T)ret;
		}
		if (t == double.class) {
			if (objClass == double.class) {
				return (T)value;
			}
			String text = GetStr(objClass, value);
			Object ret = Double.parseDouble(text);
			return (T)ret;
		}
		if (t == float.class) {
			if (objClass == float.class) {
				return (T)value;
			}
			String text = GetStr(objClass, value);
			Object ret = Float.parseFloat(text);
			return (T)ret;
		}
		if (t == BigDecimal.class) {
			if (objClass == BigDecimal.class) {
				return (T)value;
			}
			String text = GetStr(objClass, value);
			return (T)new BigDecimal(text);
		}

		if (t == java.util.Date.class){
			if (objClass == java.util.Date.class) {
				return (T)value;
			}
			String text = GetStr(objClass, value);
			return (T)HiTypeHelper.Convert2Date(text);
		}

		if (t == java.sql.Date.class){
			if (objClass == java.sql.Date.class) {
				return (T)value;
			}
			String text = GetStr(objClass, value);
			return (T)HiTypeHelper.Convert2SqlDate(text);
		}
		if (t == Time.class) {
			if (objClass == Time.class) {
				return (T)value;
			}
			String text = GetStr(objClass, value);
			Object ret = HiTypeHelper.Convert2Date(text).getTime();
			return (T)ret;
		}
		if (t == Timestamp.class) {
			if (objClass == Timestamp.class) {
				return (T)value;
			}
			String text = GetStr(objClass, value);
			return (T)Timestamp.valueOf(text);
		}
		return (T)value;
	}

3: 测试代码:

	@Test
	public void Test_HiTypeHelper_Cast() {
		Integer val = 1;
		int ret = HiTypeHelper.Cast(int.class, val);
		Assert.assertEquals(ret, 1);
		String text = "1";
		ret = HiTypeHelper.Cast(int.class, text);
		Assert.assertEquals(ret, 1);
		text = "a";
		ret = HiTypeHelper.Cast(int.class, text);
		Assert.assertEquals(ret, -1);
		int val2 = 1;
		Integer ret2 = HiTypeHelper.Cast(Integer.class, val2);
		Assert.assertEquals(ret2.intValue(), 1);
		text = "1";
		ret2 = HiTypeHelper.Cast(Integer.class, text);
		Assert.assertEquals(ret2.intValue(), 1);
		boolean bl = HiTypeHelper.Cast(boolean.class, 1);
		Assert.assertTrue(bl);
		bl = HiTypeHelper.Cast(boolean.class, 3);
		Assert.assertTrue(bl);
		bl = HiTypeHelper.Cast(boolean.class, 0);
		Assert.assertFalse(bl);
		bl = HiTypeHelper.Cast(boolean.class, -1);
		Assert.assertFalse(bl);
		bl = HiTypeHelper.Cast(boolean.class, "1");
		Assert.assertTrue(bl);
		bl = HiTypeHelper.Cast(boolean.class, "3");
		Assert.assertTrue(bl);
		bl = HiTypeHelper.Cast(boolean.class, "0");
		Assert.assertFalse(bl);
		bl = HiTypeHelper.Cast(boolean.class, "-1");
		Assert.assertFalse(bl);
	}

很多时候,数据转换在与数据库交互时使用较多,所以需要提供一些数据库类型的转换,主要是指时间或日期的转换.如:java.util.Date,java.sql.date与String和long之间的转换,下面是我的实现:

    /**
     * 字符串转换成日期
     * @param text
     * @return
     */
    public static java.util.Date Convert2Date(String text) {
    	if (text == null || text.trim() == "") {
    		return null;
    	}
		String format = "yyyy-MM-dd";
		String str = text.trim();
		if (str.contains(":")) {
			format = "yyyy-MM-dd HH:mm:ss";
		}
		SimpleDateFormat sdf = new SimpleDateFormat(format);
		try {
			return sdf.parse(str);
		} catch (ParseException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			return null;
		}
    }

    /**
     * 字符串转换为日期
     * @param text
     * @return
     */
    public static java.sql.Date Convert2SqlDate(String text) {
		java.util.Date dt = Convert2Date(text);
		return new java.sql.Date(dt.getTime());
    }

    /**
     * 日期转换为字符串
     * @param date
     * @return
     */
    public static String ToShortString(java.util.Date date) {
    	if (date == null) {
    		return null;
    	}
		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
		return sdf.format(date);
    }

    /**
     * 日期转换为字符串
     * @param date
     * @return
     */
    public static String ToLongString(java.util.Date date) {
    	if (date == null) {
    		return null;
    	}
		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		return sdf.format(date);
    }
    /**
     * 日期转换为字符串
     * @param date
     * @return
     */
    public static String ToShortString(java.sql.Date date) {
    	if (date == null) {
    		return null;
    	}
		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
		return sdf.format(date);
    }

    /**
     * 日期转换为字符串
     * @param date
     * @return
     */
    public static String ToLongString(java.sql.Date date) {
    	if (date == null) {
    		return null;
    	}
		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		return sdf.format(date);
    }