Java对List对象进行排序

转：http://my.oschina.net/baishi/blog/367699

有时候需要对List对象进行排序，如果每一处都去写一个排序方法，就会产生重复代码的坏味道，而且每一处都写，工作量会很大。
我们知道，Java提供了一个Collections.sort()方法可以对List排序，利用Java反射机制，很容易就能写出一个通用的排序方法。

为了防止出现不按照getter,setter规范命名的POJO类，我不打算动态调用getXXX()方法，而是直接获取对象的属性值。为了达到不论是否是public成员变量，都能获取到的目的，在获取到Field后，调用了setAccessible(true); 来设置访问权限。
具体代码如下：

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    /**
         * 对List对象按照某个成员变量进行排序
         * @param list       List对象
         * @param sortField  排序的属性名称
         * @param sortMode   排序方式：ASC，DESC 任选其一
         */ 
        public static <T> void sortList(List<T> list, final String sortField, final String sortMode) { 
            Collections.sort(list, new Comparator<T>() { 
                @Override 
                public int compare(T o1, T o2) { 
                    try { 
                        Class clazz = o1.getClass(); 
                        Field field = clazz.getDeclaredField(sortField); //获取成员变量 
                        field.setAccessible(true); //设置成可访问状态 
                        String typeName = field.getType().getName().toLowerCase(); //转换成小写 
     
                        Object v1 = field.get(o1); //获取field的值 
                        Object v2 = field.get(o2); //获取field的值 
     
                        boolean ASC_order = (sortMode == null || "ASC".equalsIgnoreCase(sortMode)); 
     
                        //判断字段数据类型，并比较大小 
                        if(typeName.endsWith("string")) { 
                            String value1 = v1.toString(); 
                            String value2 = v2.toString(); 
                            return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1); 
                        } 
                        else if(typeName.endsWith("short")) { 
                            Short value1 = Short.parseShort(v1.toString()); 
                            Short value2 = Short.parseShort(v2.toString()); 
                            return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1); 
                        } 
                        else if(typeName.endsWith("byte")) { 
                            Byte value1 = Byte.parseByte(v1.toString()); 
                            Byte value2 = Byte.parseByte(v2.toString()); 
                            return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1); 
                        } 
                        else if(typeName.endsWith("char")) { 
                            Integer value1 = (int)(v1.toString().charAt(0)); 
                            Integer value2 = (int)(v2.toString().charAt(0)); 
                            return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1); 
                        } 
                        else if(typeName.endsWith("int") || typeName.endsWith("integer")) { 
                            Integer value1 = Integer.parseInt(v1.toString()); 
                            Integer value2 = Integer.parseInt(v2.toString()); 
                            return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1); 
                        } 
                        else if(typeName.endsWith("long")) { 
                            Long value1 = Long.parseLong(v1.toString()); 
                            Long value2 = Long.parseLong(v2.toString()); 
                            return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1); 
                        } 
                        else if(typeName.endsWith("float")) { 
                            Float value1 = Float.parseFloat(v1.toString()); 
                            Float value2 = Float.parseFloat(v2.toString()); 
                            return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1); 
                        } 
                        else if(typeName.endsWith("double")) { 
                            Double value1 = Double.parseDouble(v1.toString()); 
                            Double value2 = Double.parseDouble(v2.toString()); 
                            return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1); 
                        } 
                        else if(typeName.endsWith("boolean")) { 
                            Boolean value1 = Boolean.parseBoolean(v1.toString()); 
                            Boolean value2 = Boolean.parseBoolean(v2.toString()); 
                            return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1); 
                        } 
                        else if(typeName.endsWith("date")) { 
                            Date value1 = (Date)(v1); 
                            Date value2 = (Date)(v2); 
                            return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1); 
                        } 
                        else if(typeName.endsWith("timestamp")) { 
                            Timestamp value1 = (Timestamp)(v1); 
                            Timestamp value2 = (Timestamp)(v2); 
                            return ASC_order ? value1.compareTo(value2) : value2.compareTo(value1); 
                        } 
                        else { 
                            //调用对象的compareTo()方法比较大小 
                            Method method = field.getType().getDeclaredMethod("compareTo", new Class[]{field.getType()}); 
                            method.setAccessible(true); //设置可访问权限 
                            int result  = (Integer)method.invoke(v1, new Object[]{v2}); 
                            return ASC_order ? result : result*(-1); 
                        } 
                    } 
                    catch (Exception e) { 
                        String err = e.getLocalizedMessage(); 
                        System.out.println(err); 
                        e.printStackTrace(); 
                    } 
     
                    return 0; //未知类型，无法比较大小 
                } 
            }); 
        }