19.12.18日结

1.最近发开中，for循环更实用写法
情景：检索Map中所有的键值对

//遍历map键值对
	for(Map.Entry entry:map.entrySet()){
		System.out.println(entry.getKey()+"="+entry.getValue()); 
	}
//Map.Entry获取Map某一个键值对
//entry.getKey()获取单个键名称
//entry.getKey()获取单个键值

情景：获取List<Object‘>每个对象的属性值，

//记录更新字段和字段值
List<Comparison> differents = new ArrayList<Comparison>();
	for(Comparison items: differents) {
	   //导出items的属性，字段名，字段旧值，字段新值
		operationStr = operationStr + ("["+items.getField()+"发生变化,"+items.getBefore()+"修改成："+items.getAfter()+"];");
		}		

格式：for（Object 对象名：集合名）{
对单个Object进行操作
}
2.如何将JSONObject数据结构转换成Bean对象？

JSONObject ObjData = JSONObject.fromObject(Obj);//Obj是前端传过来的Json数据结构的字符串
DeviceFun devNew = (DeviceFun)JSONObject.toBean(ObjData,DeviceFun.class);

3.如何记录Bean的值变化，存入日志表中？

• 创建记录变化的对照实体Bean，Bean名称：Comparison。

public class Comparison {
    
    //字段名称
    private String Field; 
    //字段旧值
    private Object before;
    //字段新值
    private Object after;
    
    /**
     * @return the field
     */
    public String getField() {
        return Field;
    }
    /**
     * @param field the field to set
     */
    public void setField(String field) {
        Field = field;
    }
    /**
     * @return the before
     */
    public Object getBefore() {
        return before;
    }
    /**
     * @param before the before to set
     */
    public void setBefore(Object before) {
        this.before = before;
    }
    /**
     * @return the after
     */
    public Object getAfter() {
        return after;
    }
    /**
     * @param after the after to set
     */
    public void setAfter(Object after) {
        this.after = after;
    }
    
}

• 创建工具类/对象比较类 CompareObjUtil

public class CompareObjUtil {

    public static List<Comparison> compareObj(Object beforeObj,Object afterObj) throws Exception{
        List<Comparison> differents = new ArrayList<Comparison>();
        
        if(beforeObj == null) throw new Exception("原对象不能为空");
        if(afterObj == null) throw new Exception("新对象不能为空");
        if(!beforeObj.getClass().isAssignableFrom(afterObj.getClass())){
            throw new Exception("两个对象不相同，无法比较");
        }
        
        //取出属性
        Field[] beforeFields = beforeObj.getClass().getDeclaredFields();
        Field[] afterFields = afterObj.getClass().getDeclaredFields();
        Field.setAccessible(beforeFields, true); 
        Field.setAccessible(afterFields, true);
        
        //遍历取出差异值
        if(beforeFields != null && beforeFields.length > 0){
            for(int i=0; i<beforeFields.length; i++){
                Object beforeValue = beforeFields[i].get(beforeObj);
                Object afterValue = afterFields[i].get(afterObj);
                    if((beforeValue != null && !"".equals(beforeValue) && !beforeValue.equals(afterValue)) || ((beforeValue == null || "".equals(beforeValue)) && afterValue != null)){
                        Comparison comparison = new Comparison();
                        comparison.setField(beforeFields[i].getName());
                        comparison.setBefore(beforeValue);
                        comparison.setAfter(afterValue);
                        differents.add(comparison);
                    }
            }
        }
        
        return differents;
    }
}

使用方法：创建对象比较类 CompareObjUti，调用方法compareObj即可。