工作上经常会遇到处理大数据的问题，下面两个工具类，是在处理大数据时编写的；推荐的是使用map的方式处理两个list数据，如果遇到list相当大数据这个方法就起到了作用，当时处理了两个十万级的list，使用改方法的变种搞定。

1.txt文件、list集合比较工具

<span style="font-family:KaiTi_GB2312;font-size:18px;">package com.hudong.util.other;

import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

import org.apache.commons.lang.StringUtils;

/**
 * txt文件对比工具
 * list集合比较工具
 * @Title: TxtCompareUtil.java
 * @Copyright: Copyright (c) 2005
 * @author 杨凯
 */
public class TxtCompareUtil {

    /**
     * 使用两个list包含来对比
     * 
     * @param input1
     * @param input2
     * @param output1
     * @param output2
     */
    public static void compareTxt(String input1, String input2, String output1, String output2) {

        List<String> listInput1 = TxtReadWriteUtil.readTxt(input1);
        List<String> listInput2 = TxtReadWriteUtil.readTxt(input2);
        for (String str : listInput1) {
            if (listInput2.contains(StringUtils.upperCase(str)) || listInput2.contains(StringUtils.lowerCase(str)) || listInput2.contains((str))) {
                TxtReadWriteUtil.writerTXT(str, output1, true);
            } else {
                TxtReadWriteUtil.writerTXT(str, output2, true);
            }
        }
    }

    /**
     * 求两个list的交集 通过求交集的方法找出两个txt的共同部分
     * 
     * @param input1
     * @param input2
     * @param output1
     * @param output2
     */
    public static void interseTxt(String input1, String input2, String output1, String output2) {
        List<String> listInput1 = TxtReadWriteUtil.readTxt(input1);
        List<String> listInput2 = TxtReadWriteUtil.readTxt(input2);
        if (listInput2.retainAll(listInput1)) {
            System.out.println(listInput2);
            // TxtReadWriteUtil.writerTXT(listInput2, output1, true);
        } else {
            // TxtReadWriteUtil.writerTXT(listInput2, output2, true);
        }
    }

    /**
     * 求两个list的并集 通过求两个list的并集来合并两个txt
     * 
     * @param input1
     * @param input2
     * @param output1
     * @param output2
     */
    public static void unionTxt(String input1, String input2, String output1, String output2) {
        List<String> listInput1 = TxtReadWriteUtil.readTxt(input1);
        List<String> listInput2 = TxtReadWriteUtil.readTxt(input2);
        listInput2.removeAll(listInput1); // 移除相同的
        listInput2.addAll(listInput1); // 放入不同的
        System.out.println(listInput2);
    }

    /**
     * 获取两个集合的不同元素
     * 
     * @param collmax
     * @param collmin
     * @return
     */
    @SuppressWarnings( { "unchecked" })
    public static Collection getDiffent(Collection collmax, Collection collmin) {
        // 使用LinkeList防止差异过大时,元素拷贝
        Collection csReturn = new LinkedList();
        Collection max = collmax;
        Collection min = collmin;
        // 先比较大小,这样会减少后续map的if判断次数
        if (collmax.size() < collmin.size()) {
            max = collmin;
            min = collmax;
        }
        // 直接指定大小,防止再散列
        Map<Object, Integer> map = new HashMap<Object, Integer>(max.size());
        for (Object object : max) {
            map.put(object, 1);
        }
        for (Object object : min) {
            if (map.get(object) == null) {
                csReturn.add(object);
            } else {
                map.put(object, 2);
            }
        }
        for (Map.Entry<Object, Integer> entry : map.entrySet()) {
            if (entry.getValue() == 1) {
                csReturn.add(entry.getKey());
            }
        }
        return csReturn;
    }

    /**
     * 获取两个集合的不同元素,去除重复
     * 
     * @param collmax
     * @param collmin
     * @return
     */
    @SuppressWarnings( {"unchecked"})
    public static Collection getDiffentNoDuplicate(Collection collmax, Collection collmin) {
        return new HashSet(getDiffent(collmax, collmin));
    }
    
    public static void main(String[] args) {
        unionTxt("e:/test/input1.txt", "e:/test/input2.txt", "e:/test/output1.txt", "e:/test/output1.txt");
    }
}
</span>

<span style="font-family:KaiTi_GB2312;font-size:18px;">package com.hudong.util.other;


import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.util.ArrayList;
import java.util.List;


import org.dom4j.io.OutputFormat;
import org.dom4j.io.XMLWriter;


/**
 * txt文件的读写操作工具
 * 
 * @Title: TxtReadWriteUtil.java
 * @Copyright: Copyright (c) 2005
 * @author 杨凯
 */
public class TxtReadWriteUtil {


    /**
     * 写txt 方式一
     * 
     * @param conent
     * @param txtPath
     * @param isAppend
     */
    public synchronized static void writerTXT(String conent, String txtPath, boolean isAppend) {
        try {
            File file = new File(txtPath);
            if (!file.getParentFile().exists()) {
                file.getParentFile().mkdirs();
            }
            if (!file.exists()) {
                file.createNewFile();
            }
            FileWriter fileWriter = new FileWriter(txtPath, isAppend);
            BufferedWriter bw = new BufferedWriter(fileWriter);
            bw.write(conent);
            bw.newLine();
            fileWriter.flush();
            bw.close();
            fileWriter.close();


        } catch (Exception e) {
            e.printStackTrace();
        }
    }


    /**
     * 写txt 方式二
     * 
     * @param file
     * @param sb
     */
    public static void createTxt(String file, StringBuffer sb) {
        try {
            OutputFormat format = OutputFormat.createPrettyPrint();
            format.setEncoding("gbk");
            format.setExpandEmptyElements(true);
            format.setTrimText(false);
            FileOutputStream fos = new FileOutputStream(file);
            XMLWriter xmlWriter = new XMLWriter(fos, format);
            xmlWriter.write(sb.toString());
            xmlWriter.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }


    /**
     * 读txt
     * 
     * @param filePath
     * @return
     */
    public static List<String> readTxt(String filePath) {
        List<String> list = new ArrayList<String>();
        try {
            BufferedReader br = new BufferedReader(new FileReader(filePath));
            String line = null;
            while ((line = br.readLine()) != null) {
                list.add(line);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return list;
    }
}</span>

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