所以我有一个大文件，里面有一堆天气数据。我必须将大文件中的每一行分配到相应的状态文件中。因此，总共将有50个新的状态文件和它们自己的数据。
这个大文件包含大约100万行这样的记录：

COOP:166657,'NEW IBERIA AIRPORT ACADIANA REGIONAL LA US',200001,177,553

虽然电台的名称可以不同，字数也不同。
目前我正在使用regex查找模式并输出到一个文件，它必须按状态分组。如果我在没有任何修改的情况下读取整个文件，大约需要46秒。使用代码查找州缩写，创建文件，并输出到该文件，需要10分钟以上的时间。
这就是我现在所拥有的：

package climate;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Arrays;
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * This program will read in a large file containing many stations and states,
 * and output in order the stations to their corresponding state file.
 * 
 * Note: This take a long time depending on processor. It also appends data to
 * the files so you must remove all the state files in the current directory
 * before running for accuracy.
 * 
 * @author Marcus
 *
 */

public class ClimateCleanStates {

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

        Scanner in = new Scanner(System.in);
        System.out
                .println("Note: This program can take a long time depending on processor.");
        System.out
                .println("It is also not necessary to run as state files are in this directory.");
        System.out
                .println("But if you would like to see how it works, you may continue.");
        System.out.println("Please remove state files before running.");
        System.out.println("\nIs the States directory empty?");
        String answer = in.nextLine();

        if (answer.equals("N")) {
            System.exit(0);
            in.close();
        }
        System.out.println("Would you like to run the program?");
        String answer2 = in.nextLine();
        if (answer2.equals("N")) {
            System.exit(0);
            in.close();
        }

        String[] statesSpaced = new String[51];

        File statefile, dir, infile;

        // Create files for each states
        dir = new File("States");
        dir.mkdir();

        infile = new File("climatedata.csv");
        FileReader fr = new FileReader(infile);
        BufferedReader br = new BufferedReader(fr);

        String line;
        line = br.readLine(); 
        System.out.println();

        // Read in climatedata.csv
        final long start = System.currentTimeMillis();
        while ((line = br.readLine()) != null) {
            // Remove instances of -9999
            if (!line.contains("-9999")) {

                        String stateFileName = null;

                        Pattern p = Pattern.compile(".* ([A-Z][A-Z]) US"); 
                        Matcher m = p.matcher(line);
                        if (m.find()){
                            stateFileName = m.group(1); 
                            stateFileName = "States/" + stateFileName + ".csv";
                            statefile = new File(stateFileName);

                            FileWriter stateWriter = new FileWriter(statefile, true);
                            stateWriter.write(line + "\n");
                            // Progress reporting
                            //System.out.printf("Writing [%s] to file [%s]\n", line,
                            //      statefile);

                            stateWriter.flush();
                            stateWriter.close();

                        } 
            }
        }
        System.out.println("Elapsed " + (System.currentTimeMillis() - start) + " ms");
        br.close();
        fr.close();
        in.close();

    }

}