关于将多个文件拼接成一个文件

Question

I work on query latencies and have a requirement where I have several files which contain data. I want to aggregate this data into a single file. I use a naive technique where I open each file and collect all the data in a global file. I do this for all the files but this is time taking. Is there a way in which you can stitch the end of one file to the beginning of another and create a big file containing all the data. I think many people might have faced this problem before. Can anyone kindly help ?

Answer 1

I suppose you are currently doing the opening and appending by hand; otherwise I do not know why it would take a long time to aggregate the data, especially since you describe the amount of files using multiple and several which seem to indicate it's not an enormous number.

Thus, I think you are just looking for a way to automatically to the opening and appending for you. In that case, you can use an approach similar to below. Note this creates the output file or overwrites it if it already exists, then appends the contents of all specified files. If you want to call the method multiple times and append to the same file instead of overwriting an existing file, an alternative is to use a FileWriter instead with true as a second argument to its constructor so it will append to an existing file.

void aggregateFiles(List<String> fileNames, String outputFile) {
    PrintWriter writer = null;
    try {
        writer = new PrintWriter(outputFile);
        for(String fileName : fileNames) {
            Path path = Paths.get(fileName);
            String fileContents = new String(Files.readAllBytes(path));
            writer.println(fileContents);
        }
    } catch(IOException e) {
        // Handle IOException
    } finally {
        if(writer != null) writer.close();
    }
}

List<String> files = new ArrayList<>();
files.add("f1.txt");
files.add("someDir/f2.txt");
files.add("f3.txt");

aggregateFiles(files, "output.txt");