Java将字符串列表写入文件，但文件为空

Question

我在其他语言中发现了这个问题，但还没有在 java 应用程序中找到解决这个问题的方法。

我有一个包含数百万条记录的大型 .txt 文件。每条记录由 /n 分隔。基本上它是表中的一列数据。目标是从输入文件中读取数据并对其进行分区。然后将分区数据写入新文件。例如，一个有 200 万条记录的文件将变成 200 个文件，每个文件有 10,000 条记录(最后一个文件包含 <10,000 条)。

我正在成功读取和分区数据。我成功创建了第一个文件，并且命名正确。

问题是只创建了 1 个文件并且它是空的。代码按原样编译和运行，没有错误或异常。

我的代码如下:

    import java.io.BufferedReader;
    import java.io.BufferedWriter;
    import java.io.FileReader;
    import java.io.FileWriter;
    import java.io.IOException;
    import java.io.StringWriter;
    import java.util.ArrayList;
    import java.util.Collection;
    import java.util.List;
    import java.util.concurrent.atomic.AtomicInteger;
    import java.util.stream.Collectors;

    public class ChunkTextFile {

    private static final String inputFilename = "inputFile.txt";

    public static void main(String[] args) {

        BufferedReader reader = null;

        BufferedWriter fileWriter = null;

        BufferedWriter lineWriter = null;

        StringWriter stringWriter = null;

        // Create an ArrayList object to hold the lines of input file

        List<String> lines = new ArrayList<String>();

        try {
            // Creating BufferedReader object to read the input file

            reader = new BufferedReader(new FileReader("src" + "//" + inputFilename));

            // Reading all the lines of input file one by one and adding them into ArrayList
            String currentLine = reader.readLine();

            while (currentLine != null) {
                lines.add(currentLine);

                currentLine = reader.readLine();

            }
            // End of file read.

           //Partition ArrayList into a collection of smaller Lists<String>
            final AtomicInteger counter = new AtomicInteger(0);
            final int size = 10000;

            Collection<List<String>> partitioned = lines.stream()
                    .collect(Collectors.groupingBy(it -> counter.getAndIncrement() / size)).values();

            //Printing partitions. Each partition will be written to a file.
            //Testing confirms the partitioning works correctly.
            partitioned.forEach(System.out::println);

            //Iterate through the Collections and create a file for List<String> object.
            //Testing confirms that multiple files are created and properly named.
            Integer count = 0;
            for (List<String> chunks : partitioned) {
                // Prepare new incremented file name.
                String outputFile = "batched_items_file_";
                String txt = ".txt";
                count++;


                String filename = outputFile + count + txt;

                // Write file to directory.
                fileWriter = new BufferedWriter(new FileWriter("src" + "//" + outputFile));
                fileWriter = new BufferedWriter(new FileWriter(filename));

                //Iterate through the List of Strings and write each String to the file.
                //Writing is not successful. Only 1 file is created and it is empty.
                for (String chunk : chunks) {
                    stringWriter = new StringWriter();
                    lineWriter = new BufferedWriter(stringWriter);
                    // Prepare list of strings to be written to new file.
                    // Write each item number to file.
                    lineWriter.write(chunk);
                    lineWriter.flush();
                }
                lineWriter.close(); // <- flush the BufferedWriter

                fileWriter.close();
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            // Closing the resources
            System.out.println("Finished");

            try {
                if (reader != null) {
                    reader.close();
                }

                if (fileWriter != null) {
                    fileWriter.close();
                }

                if (stringWriter != null) {
                    stringWriter.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

输入文件示例:

230449
235659
295377
329921
348526
359836
361447
384723
396202
571490

提前谢谢你。

Answer 1

您的 for 中不需要所有这些额外的写入器，并且不会调用应该写入 (fileWriter) 到文件的写入器。用这个替换你的 for:

for (String chunk : chunks) {
    fileWriter.write(chunk);
}

提示:只需在 finally block 中调用 fileWriter.close() 一次。 close 方法会自动为您刷新 writer(无需调用 fileWriter.flush())。