OpenCSV 避免使用 FileWriter 并返回 InputStream

Question

我正在使用OpenCsv，new CSVWriter()方法将Writer作为参数。

我试图实现的是避免写入文件系统，而是返回InputStream。我不知道该怎么做。不太熟悉Streams我也在使用JAVA 7.

我是否有可能使 writeValues 方法返回输入流并避免在文件系统上写入输出。

这是我的工作实现：

private static void writeValues(String[][] cellValues) throws IOException {
    CSVWriter writer = new CSVWriter(new FileWriter("/tmp/myfile.csv"));
    for(String[] row : cellValues) { 
        writer.writeNext(row);
    }
    writer.close();
}

这就是我想要实现的目标。如何转换上述方法以避免使用文件编写器。

private static InputStream writeValues(String[][] cellValues) throws IOException {
    InputStream inputStream = ?;
    CSVWriter writer = new CSVWriter(?);
    for(String[] row : cellValues) { 
        writer.writeNext(row);
    }
    writer.close();
    return inputStream;
}

Answer 1

将 Bean 转换为字节数组的示例实现：

public static byte[] getBeansAsByteArray(final List<YourBean> beans) {
    ByteArrayOutputStream stream = new ByteArrayOutputStream();
    OutputStreamWriter streamWriter = new OutputStreamWriter(stream);
    CSVWriter writer = new CSVWriter(streamWriter);
    StatefulBeanToCsv<YourBean> beanToCsv = new StatefulBeanToCsvBuilder(writer).build();
    beanToCsv.write(beans);
    streamWriter.flush();
    
    return stream.toByteArray();
}

Answer 2

写入OutpuStreamWriter本身写入ByteArrayOutputStream，最后，您将在内存中拥有一个字节数组（通过在ByteArrayOutputStream上调用getBytes()）。

然后，您可以通过在字节数组上打开一个ByteArrayInputStream来读取此字节数组。

Answer 3

获取一个没有 StatefulBeanToCsv 的工作片段，我不喜欢。

 String[] headers = { "id", "result", "searchTerm"};
 ByteArrayOutputStream stream = new ByteArrayOutputStream();
 OutputStreamWriter streamWriter = new OutputStreamWriter(stream);
 CSVWriter writer = new CSVWriter(streamWriter);
 writer.writeNext(headers);
 // listOfRows -> business logic collection containing data for csv rows, as you can see I've separated the declaration of headers 
 listOfRows.forEach(it -> {
        writer.writeNext(new String[] {it.getId().toString(), it.getResult(), it.getSearchTerm()});
 });
 streamWriter.flush();
 byte[] byteArrayOutputStream = stream.toByteArray();

Answer 4

这是正确的实现

public static byte[] getBeansAsByteArray(List<YourBean> beans) {
    ByteArrayOutputStream stream = new ByteArrayOutputStream();
    OutputStreamWriter streamWriter = new OutputStreamWriter(stream);
    CSVWriter writer = new CSVWriter(streamWriter);
    StatefulBeanToCsv<YourBean> beanToCsv = new StatefulBeanToCsvBuilder(writer).build();
    beanToCsv.write(beans);
    streamWriter.flush();
    return stream.toByteArray();
}