一、业务场景
相信很多开发的小伙伴都有遇到过需要对表按特定条件进行查询,然后再进行归类,比如:对员工表进行检索,然后分别按他们所在的部门进行归类,一般的做法都是按部门唯一标识(比如部门编号、部门名称等)进行一次一次查询,这样做的缺点显而易见,会造成与数据库的多次连接,从而影响效率和性能。而我的做法是直接对员工表进行一次全部读取,然后在本地根据条件再进行归类,这就涉及到需要对List进行处理,将父List直接拆分成多个子List。当然,上面举的例子只是最简单的业务场景,实际场景可能错综复杂,但
二、Java实现
话不多说,直接上代码。当然,上面举的例子只是最简单的业务场景,实际场景可能错综复杂,但我下面提供参考的这段代码已经够用了。
package com.ruoyi.web.test;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
public class DealList {
/**
* 按照List<Map<String,Object>>里面map的某个value重新封装成多个不同的list, 原始数据类型List<Map
* <String,Object>>, 转换后数据类型Map<String,List<Map<String,Object>>>
*
* @param list
* @param oneMapKey
* @return
*/
private static List<Map<String, Object>> change(List<Map<String, Object>> inList, String oneMapKey,
List<Map<String, Object>> outList) {
// 1.将某个key的值存在set中
Set<Object> setTmp = new HashSet<Object>();
for (Map<String, Object> tmp : inList) {
setTmp.add(tmp.get(oneMapKey));
}
// 2.遍历set
Iterator<Object> it = setTmp.iterator();
while (it.hasNext()) {
String oneMapValueStr = "";
String oneSetTmpStr = (String) it.next();
Map<String, Object> oneSetTmpMap = new HashMap<String, Object>();
List<Map<String, Object>> oneSetTmpList = new ArrayList<Map<String, Object>>();
for (Map<String, Object> tmp : inList) {
oneMapValueStr = (String) tmp.get(oneMapKey);
if (oneSetTmpStr.equals(oneMapValueStr)) {
oneSetTmpMap.put("text", oneSetTmpStr);
oneSetTmpList.add(tmp);
}
}
oneSetTmpMap.put("array", oneSetTmpList);
outList.add(oneSetTmpMap);
}
return outList;
}
public static void main(String[] args) {
Map<String, Object> map1 = new HashMap<String, Object>();
Map<String, Object> map2 = new HashMap<String, Object>();
Map<String, Object> map3 = new HashMap<String, Object>();
Map<String, Object> map4 = new HashMap<String, Object>();
List<Map<String, Object>> inList = new ArrayList<Map<String, Object>>();
map1.put("dept", "开发部");
map1.put("name", "张三");
map2.put("dept", "业务部");
map2.put("name", "李华");
map3.put("dept", "开发部");
map3.put("name", "李四");
map4.put("dept", "业务部");
map4.put("name", "王明");
inList.add(map1);
inList.add(map2);
inList.add(map3);
inList.add(map4);
System.out.println("原始的List:" + inList);
List<Map<String, Object>> outList = new ArrayList<Map<String, Object>>();
outList = change(inList, "dept", outList);
System.out.println("处理后的List:" + outList);
}
}
结果:
原始的List:[{name=张三, dept=开发部}, {name=李华, dept=业务部}, {name=李四, dept=开发部}, {name=王明, dept=业务部}]
处理后的List:[{array=[{name=张三, dept=开发部}, {name=李四, dept=开发部}], text=开发部}, {array=[{name=李华, dept=业务部}, {name=王明, dept=业务部}], text=业务部}]