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:

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/**
     * 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);
        }
    }

　　

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

　　

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@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:

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@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:

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/**
 * 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);
}

　　

 

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