大数据Java基础第十五天作业

Posted 2020-07-22

第一题：实现文件拆分、合并。
import java.io.File;
import java.io.RandomAccessFile;
import java.io.FileOutputStream;
import java.io.FileInputStream;
import java.io.BufferedOutputStream;
import java.io.BufferedInputStream;
import java.util.List;
import java.util.ArrayList;

class RandomDome{
    public static void main(String[] args) throws Exception{
        randomSplit("e:/index.txt",3,5);
        List<String> inpath_list = new ArrayList<String>();
        inpath_list.add("e:/index0.txt");
        inpath_list.add("e:/index1.txt");
        inpath_list.add("e:/index2.txt");
        randomMerge("e:/index3.txt",inpath_list);
    }

    public static void randomSplit(String inpath,String outpath,int num,int buf_length) throws Exception{
        File file = new File(inpath);
        RandomAccessFile raf = new RandomAccessFile(file,"r");
        long file_length = file.length();
        int avg_length = (int)file_length / 3;
        for(int i=0;i<num;i++){
            int start_index = i * avg_length;
            int end_index = 0;
            if(i == (num - 1)){
                end_index = (int)file_length - 1;
            }else{
                end_index = (i + 1) * avg_length - 1;
            }
            raf.seek(start_index);
            BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(outpath + i));
            byte[] buf = new byte[buf_length];
            System.out.println(start_index + "---" + end_index);
            while(true){
                int current_index = (int)raf.getFilePointer();
                int remain = end_index - current_index + 1;
                System.out.println(current_index + "---" + remain);
                if(remain >= buf.length){
                    raf.read(buf);
                    out.write(buf);
                }else{
                    raf.read(buf,0,remain);
                    out.write(buf,0,remain);
                }
                if(raf.getFilePointer() > end_index){
                    break;
                }    
            }
            out.close();
        }
        raf.close();
    }
    public static void randomMerge(String outpath,List<String> inpath_list) throws Exception{
        BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(outpath));
        for(String inpath : inpath_list){
            BufferedInputStream in = new BufferedInputStream(new FileInputStream(inpath));
            byte[] buf = new byte[1024];
            int len;
            while((len = in.read(buf)) != -1){
                out.write(buf,0,len);
            }
            in.close();
        }
        out.close();
    }
}

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