How do InputStream, InputStreamReader and BufferedReader work in Java?

Question

I am studying Android development (I am new to programming in general) and found out about the HTTP network and saw this code in the lesson:

private String readFromStream(InputStream inputStream) throws IOException {
  StringBuilder output = new StringBuilder();
  if (inputStream != null) {
    InputStreamReader inputStreamReader = new InputStreamReader(inputStream, Charset.forName("UTF-8"));
    BufferedReader reader = new BufferedReader(inputStreamReader);
    String line = reader.readLine();
    while (line != null) {
      output.append(line);
      line = reader.readLine();
    }
  }
  return output.toString();
}

I do not understand what InputStream, InputStreamReader and BufferedReader do. They all have a read () method, as well as readLine () in the case of BufferedReader. Why can't I use InputStream or add only InputStreamReader? Why do I need to add a BufferedReader? I know that this is related to efficiency, but I don’t understand how to do it.

I researched and the documentation for BufferedReader is trying to explain this, but I still don't understand who is doing what:

, , Reader, , . BufferedReader Reader read() , FileReaders InputStreamReaders. ,

BufferedReader in = new BufferedReader(new FileReader("foo.in")); . read() readLine() , , , , .

, , InputStream , InputStreamReader - , BufferedReader - - , . , , , .

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, BufferedReader readLine() readStream InputStreamReader, readStream read()? InputStream , int, , InputStreamReader , int , BufferedReader , ? , , ? , , .

!

Answer 1

Java , .

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Reader/Writer
. .

BufferedReader/BufferedWriter
. .

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InputStreams
InputStreams java. , , ..

, FileInputStream . ByteArrayInputStream .

OutputStream
. InputStream OutputStream, .

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UPDATE

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FileInputStream, BufferedInputStream, class BufferedInputStream FileInputStream . () , FileInputStream , . BufferedOutputStream FileOutputStream.

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Answer 2

• InputStream, OutputStream, byte[], ByteBuffer .

• Reader, Writer, String, char text, Unicode, (, ).

• InputStreamReader OutputStreamWriter . InputStream , , Charset, InputStream:

  try (InputStreamReader reader =
          new InputStreamReader(stream, StandardCharsets.UTF_8)) {
       ... read text ...
  }
  

Charset, , .

Android StandardCharset , "UTF-8".

FileInputStream BufferedReader - InputStream . Reader.

FileInputStream , BufferedReader , (). new BufferedReader(otherReader) .

, Files , newBufferedReader(Path, Charset), .