Map 按照 value排序

场景： 需要统计errorMsg的数量， 从大到小排序。 errorMsg为key， 数量为value。

按照key排序 很简单，TreeMap就ok。

按值排序就相对麻烦些了，貌似没有直接可用的数据结构能处理类似需求，需要我们自己转换一下。
Map本身按值排序是很有意义的，很多场合下都会遇到类似需求，可以认为其值是定义的某种规则或者权重。

原理：将待排序Map中的所有元素置于一个列表中，接着使用Collections的一个静态方法 sort(List<T> list, Comparator<? super T> c)
来排序列表，同样是用比较器定义比较规则。排序后的列表中的元素再依次装入Map，为了肯定的保证Map中元素与排序后的List中的元素的顺序一致，使用了LinkedHashMap数据类型。

package com.tristan;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.Collections;
import java.util.Comparator;
import java.util.Date;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;
import java.util.Map.Entry;

import com.hp.hpsc.logview.client.LogviewClient;
import com.hp.hpsc.logview.po.Link;

public class TestA {

	public static void main(String[] args) throws Exception {

		/*
		 * // linux String file = "/opt/sasuapps/itrc/logs/logview/info.log";
		 * String folder = "/opt/sasuapps/itrc/logs";
		 * 
		 * LogviewClient client = new LogviewClient(); List<Link> list =
		 * client.readDirectory(folder); for (Link link : list) {
		 * System.out.println(link.getName()); }
		 * 
		 * LogviewClient client2 = new LogviewClient(); client2.readLog(file);
		 */

		// now
		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
		String nowS = "2014-03-18";
		Date nowD = sdf.parse(nowS);
		Calendar nowC = Calendar.getInstance();
		nowC.setTime(nowD);

		String folder = "/opt/sasuapps/itrc/logs/sp4tsusergroup/main/error";

		LogviewClient client = new LogviewClient();
		List<Link> list = client.readDirectory(folder);

		// check file last modified date
		SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy-MM-dd");
		List<String> fileList = new ArrayList<String>();
		for (Link link : list) {
			if (!link.isFolderFlag()) {

				String s1 = link.getLastModifiedDate();
				Date d1 = sdf1.parse(s1);

				Calendar c1 = Calendar.getInstance();
				c1.setTime(d1);

				Calendar nowMinus2 = Calendar.getInstance();
				nowMinus2.setTime(nowD);
				nowMinus2.add(Calendar.DATE, -2);

				if (c1.after(nowMinus2)) {
					System.out.println(link.getName());
					fileList.add(link.getUri());
				}
			}
		}

		// get the content which match the date like 03/21/2013
		SimpleDateFormat sdf2 = new SimpleDateFormat("MM/dd/yyyy");
		LogviewClient client2 = new LogviewClient();
		List<String> errorList = new ArrayList<String>();

		for (String file : fileList) {
			InputStream input = client2.loadInputStream(file);
			InputStreamReader isr = new InputStreamReader(input);
			BufferedReader br = new BufferedReader(isr);
			String temp = "";
			while ((temp = br.readLine()) != null) {
				if (temp.length() > 10) {
					String s1 = temp.substring(0, 10);
					Date d1 = null;

					try {
						d1 = sdf2.parse(s1);
					} catch (Exception e) {
						continue;
					}

					Calendar c1 = Calendar.getInstance();
					c1.setTime(d1);

					Calendar nowMinus2 = Calendar.getInstance();
					nowMinus2.setTime(nowD);
					nowMinus2.add(Calendar.DATE, -2);

					Calendar nowMinus1 = Calendar.getInstance();
					nowMinus1.setTime(nowD);
					nowMinus1.add(Calendar.DATE, -1);


					if (c1.after(nowMinus2) && c1.before(nowC)) {
						errorList.add(temp);
					}
				}

			}
			br.close();
			isr.close();
			input.close();
		}

		// parse error list
		List<String> errorMsgList = new ArrayList<String>();
		for (String error : errorList) {
			int begin = error.indexOf("{");
			String s1 = error.substring(begin + 1);

			int end = s1.indexOf(":");
			s1 = s1.substring(0, end);
			errorMsgList.add(s1);
		}


		// statistics
		Map<String, Integer> map = new HashMap<String, Integer>();

		for (String temp : errorMsgList) {
			Integer count = map.get(temp);
			map.put(temp, (count == null) ? 1 : count + 1);
		}

		//sort
		Map<String, Integer> resultMap = sortMapByValue(map);

		for (String key : resultMap.keySet()) {
			System.out.println(resultMap.get(key) + " : " + key);
		}

	}

	public static Map<String, Integer> sortMapByValue(
			Map<String, Integer> oriMap) {
		if (oriMap == null || oriMap.isEmpty()) {
			return null;
		}
		
		List<Map.Entry<String, Integer>> entryList = new ArrayList<Map.Entry<String, Integer>>(
				oriMap.entrySet());

		Collections.sort(entryList, new MapValueComparator());

		Map<String, Integer> sortedMap = new LinkedHashMap<String, Integer>();
		
		for(Map.Entry<String, Integer> entry : entryList){
			sortedMap.put(entry.getKey(), entry.getValue());
		}
		
		return sortedMap;
	}
}

class MapValueComparator implements Comparator<Map.Entry<String, Integer>> {

	@Override
	public int compare(Entry<String, Integer> me1, Entry<String, Integer> me2) {

		return me2.getValue().compareTo(me1.getValue());
	}
}

参考
http://blog.csdn.net/top_code/article/details/8528954