大文件读写

    import java.io.BufferedInputStream;
    import java.io.BufferedReader;
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.FileWriter;
    import java.io.IOException;
    import java.io.InputStreamReader;  

    public class FileSplit
    {
        public static void main(String[] args) throws IOException
        {
            long timer = System.currentTimeMillis();
            int bufferSize = 20 * 1024 * 1024;//设读取文件的缓存为20MB  

            //建立缓冲文本输入流
            File file = new File("/media/Data/毕业设计/kdd cup/数据/userid_profile.txt");
            FileInputStream fileInputStream = new FileInputStream(file);
            BufferedInputStream bufferedInputStream = new BufferedInputStream(fileInputStream);
            InputStreamReader inputStreamReader = new InputStreamReader(bufferedInputStream);
            BufferedReader input = new BufferedReader(inputStreamReader, bufferSize);  

            int splitNum = 112-1;//要分割的块数减一
            int fileLines = 23669283;//输入文件的行数
            long perSplitLines = fileLines / splitNum;//每个块的行数
            for (int i = 0; i <= splitNum; ++i)
            {
                //分割
                //每个块建立一个输出
                FileWriter output = new FileWriter("/home/haoqiong/part" + i + ".txt");
                String line = null;
                //逐行读取，逐行输出
                for (long lineCounter = 0; lineCounter < perSplitLines && (line = input.readLine()) != null; ++lineCounter)
                {
                    output.append(line + "\r");
                }
                output.flush();
                output.close();
                output = null;
            }
            input.close();
            timer = System.currentTimeMillis() - timer;
            System.out.println("处理时间：" + timer);
        }
    }  

方法2

void largeFileIO(String inputFile, String outputFile) {
        try {
            BufferedInputStream bis = new BufferedInputStream(new FileInputStream(new File(inputFile)));
            BufferedReader in = new BufferedReader(new InputStreamReader(bis, "utf-8"), 10 * 1024 * 1024);//10M缓存
            FileWriter fw = new FileWriter(outputFile);
            while (in.ready()) {
                String line = in.readLine();
                fw.append(line + " ");
            }
            in.close();
            fw.flush();
            fw.close();
        } catch (IOException ex) {
            ex.printStackTrace();
        }