Java InputStreamReader

last modified March 3, 2024

In this article we show how to use Java InputStreamReader to read text in Java.

JavaInputStreamReader is a bridge between byte streams and character streams. It reads bytes and decodes them into characters using a specified charset.

It is recommended to wrap an InputStreamReader within a BufferedReader for optimal efficiency.

Note that when working with character streams in Java, we should avoid using streams that rely on default encoding, such as FileReader or PrintWriter.

Reading from a FileInputStream

In the first example, we use InputStreamReader to read text from a file stream.

russian-text.txt

Пе́рвая мирова́я война́ (28 июля 1914 — 11 ноября 1918) — один из самых широкомасштабных вооружённых конфликтов в истории человечества. Формальным поводом к войне послужили события в Сараеве, где 28 июня 1914 года девятнадцатилетний боснийский серб, студент Гаврило Принцип осуществил покушение, в результате которого был убит австрийский эрцгерцог Франц Фердинанд и его морганатическая жена София Хотек.

We have a text in Cyrillic.

Main.java

import java.io.BufferedReader; import java.io.FileInputStream; import java.io.InputStreamReader; import java.nio.charset.StandardCharsets;

void main() throws Exception {

String fileName = "russian-text.txt";

try (var fis = new FileInputStream(fileName);
        var isr = new InputStreamReader(fis, StandardCharsets.UTF_8);
        var br = new BufferedReader(isr)) {

    String line;

    while ((line = br.readLine()) != null) {
        System.out.println(line);
    }
}

}

The example reads a small text in Russian language.

try (var fis = new FileInputStream(fileName); var isr = new InputStreamReader(fis, StandardCharsets.UTF_8); var br = new BufferedReader(isr)) {

A FileInputStream is used to create a file stream. The FileInputStream is wrapped into a InputStreamReader for reading text data. We set the StandardCharsets.UTF_8 encoding. Finally, the InputStreamReader is wrapped into a BufferedReader for optimal efficiency.

Reading from standard input stream

The second example uses InputStreamReader to read text from standard input stream.

Main.java

import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.nio.charset.StandardCharsets;

void main() throws IOException {

try (var br = new BufferedReader(new InputStreamReader(System.in,
                StandardCharsets.UTF_8))) {

    String line;
    System.out.print("Give me a cookie: ");

    while (!(("cookie").equals(line = br.readLine()))) {

        System.out.println(line);
        System.out.print("Give me a cookie: ");
    }
}

}

The example prints a prompt and awaits a response from a user. The program ends when it receives the correct input.

try (var br = new BufferedReader(new InputStreamReader(System.in, StandardCharsets.UTF_8))) {

We use System.in to read from standard input.

Reading from URL stream

The following example reads text from a network stream with InputStreamReader.

Main.java

import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.net.URI; import java.nio.charset.StandardCharsets;

void main() throws IOException {

var url = URI.create("https://www.webcode.me").toURL();

try (var isr = new InputStreamReader(url.openStream(), StandardCharsets.UTF_8);
        var br = new BufferedReader(isr)) {

    String line;
    var sb = new StringBuilder();

    while ((line = br.readLine()) != null) {

        sb.append(line);
        sb.append(System.lineSeparator());
    }

    System.out.println(sb.toString());
}

}

The example reads text from a website.

try (var isr = new InputStreamReader(url.openStream(), StandardCharsets.UTF_8); var br = new BufferedReader(isr)) {

The example opens a stream from the specified URL. It reads HTML code from the webcode.me webpage.

Source

Java InputStreamReader - language reference

In this article we have shown how to work with Java InputStreamReader to read text in Java.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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