Beanio-如何写入流对象

Question

我正在尝试使用 beanio 创建固定长度的文件输出。我不想写入物理文件，而是想将内容写入 OutputStream。

ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
StreamFactory factory = StreamFactory.newInstance(); 
StreamBuilder builder = new StreamBuilder("sb")
            .format("fixedlength")
            .parser(new FixedLengthParserBuilder())
            .addRecord(Team.class);

factory.define(builder);
OutputStreamWriter writer = new OutputStreamWriter(outputStream, StandardCharsets.UTF_8);
BeanWriter bw = sf.createWriter("sb", writer);

bw.write(teamVO) // teamVO has some value.

try(OutputStream os = new FileOutputStream("file.txt")){
    outputStream.writeTo(os); //Doing this only to check outputStream has some value
}

这里创建的文件 file.txt 没有内容，大小为 0 kb。

我可以用以下方法写入文件，但由于我不想在物理位置写入文件，所以我想到将内容写入到outputStream中，然后用不同的方法将其转换为到文件

//This is working and creates file successfully
StreamFactory factory = StreamFactory.newInstance();
StreamBuilder builder = new StreamBuilder("sb")
                .format("fixedlength")
                .parser(new FixedLengthParserBuilder())
                .addRecord(Team.class)
        
factory.define(builder);
BeanWriter bw = factory.createWriter("sb", new File("file.txt"));
bw.write(teamVO);

为什么在第一种方法中创建的文件大小为 0 kb？

Answer 1

您似乎没有向 OutputstreamWriter 写入足够的数据，无法将一些数据推送到底层 ByteArrayOutputStream。这里你有两个选择。

1. 手动刷新 writer 对象，然后将其关闭。然后，这会将数据写入outputStream。我不推荐这种方法，因为如果在手动刷新和关闭写入器之前出现任何异常，写入器可能不会被刷新或关闭。
2. 为 writer 使用 try-with-resource 块，它应该负责关闭 writer 并最终将数据刷新到 outputStream

这应该可以解决问题：

final ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
try (final OutputStreamWriter writer = new OutputStreamWriter(outputStream) ) {
  final BeanWriter bw = factory.createWriter("sb", writer);

  final Team teamVO = new Team();
  teamVO.setName("TESTING");

  bw.write(teamVO); // teamVO has some value.
}

try (OutputStream os = new FileOutputStream("file.txt") ) {
  outputStream.writeTo(os); // Doing this only to check outputStream has some value
}