Java : InputStreamReader with Examples

InputStreamReader (Java SE 21 & JDK 21) with Examples.
You will find code examples on most InputStreamReader methods.

Summary

An InputStreamReader is a bridge from byte streams to character streams: It reads bytes and decodes them into characters using a specified charset. The charset that it uses may be specified by name or may be given explicitly, or the default charset may be used.

Class diagram

final byte[] bytes = "abc".getBytes();

try (final var reader = new InputStreamReader(new ByteArrayInputStream(bytes))) {
    final var ret1 = reader.read();
    System.out.printf("%d : %c%n", ret1, ret1); // 97 : a

    final var ret2 = reader.read();
    System.out.printf("%d : %c%n", ret2, ret2); // 98 : b

    final var ret3 = reader.read();
    System.out.printf("%d : %c%n", ret3, ret3); // 99 : c

    final var ret4 = reader.read();
    System.out.println(ret4); // -1
}

final byte[] bytes = """
        abcd
        XYZ
        12345
        """.getBytes();

try (final var reader = new BufferedReader(new InputStreamReader(
        new ByteArrayInputStream(bytes)))) {
    System.out.println(reader.readLine()); // abcd
    System.out.println(reader.readLine()); // XYZ
    System.out.println(reader.readLine()); // 12345
    System.out.println(reader.readLine()); // null
}

Fields declared in Reader

lock

Please see the link below.

Reader with Examples

Constructors

InputStreamReader (InputStream in)

Creates an InputStreamReader that uses the default charset.

final byte[] bytes = "abc".getBytes();

try (final var reader = new InputStreamReader(new ByteArrayInputStream(bytes))) {
    final var ret1 = reader.read();
    System.out.printf("%d : %c%n", ret1, ret1); // 97 : a

    final var ret2 = reader.read();
    System.out.printf("%d : %c%n", ret2, ret2); // 98 : b

    final var ret3 = reader.read();
    System.out.printf("%d : %c%n", ret3, ret3); // 99 : c

    final var ret4 = reader.read();
    System.out.println(ret4); // -1
}

InputStreamReader (InputStream in, String charsetName)

Creates an InputStreamReader that uses the named charset.

final var sjis = "Shift_JIS";
final byte[] bytes = "○△×".getBytes(sjis);

try (final var reader = new InputStreamReader(
        new ByteArrayInputStream(bytes), sjis)) {
    final var ret1 = reader.read();
    System.out.printf("%d : %c%n", ret1, ret1); // 9675 : ○

    final var ret2 = reader.read();
    System.out.printf("%d : %c%n", ret2, ret2); // 9651 : △

    final var ret3 = reader.read();
    System.out.printf("%d : %c%n", ret3, ret3); // 215 : ×

    final var ret4 = reader.read();
    System.out.println(ret4); // -1
}

InputStreamReader (InputStream in, Charset cs)

Creates an InputStreamReader that uses the given charset.

final var sjis = Charset.forName("Shift_JIS");
final byte[] bytes = "○△×".getBytes(sjis);

try (final var reader = new InputStreamReader(
        new ByteArrayInputStream(bytes), sjis)) {
    final var ret1 = reader.read();
    System.out.printf("%d : %c%n", ret1, ret1); // 9675 : ○

    final var ret2 = reader.read();
    System.out.printf("%d : %c%n", ret2, ret2); // 9651 : △

    final var ret3 = reader.read();
    System.out.printf("%d : %c%n", ret3, ret3); // 215 : ×

    final var ret4 = reader.read();
    System.out.println(ret4); // -1
}

InputStreamReader (InputStream in, CharsetDecoder dec)

Creates an InputStreamReader that uses the given charset decoder.

final var sjis = Charset.forName("Shift_JIS");
final byte[] bytes = "○△×".getBytes(sjis);

try (final var reader = new InputStreamReader(
        new ByteArrayInputStream(bytes), sjis.newDecoder())) {
    final var ret1 = reader.read();
    System.out.printf("%d : %c%n", ret1, ret1); // 9675 : ○

    final var ret2 = reader.read();
    System.out.printf("%d : %c%n", ret2, ret2); // 9651 : △

    final var ret3 = reader.read();
    System.out.printf("%d : %c%n", ret3, ret3); // 215 : ×

    final var ret4 = reader.read();
    System.out.println(ret4); // -1
}

Methods

void close ()

Closes the stream and releases any system resources associated with it.

final byte[] bytes = "abcd".getBytes();
try (final var reader = new InputStreamReader(new ByteArrayInputStream(bytes))) {
    final var cbuf = new char[4];

    System.out.println(reader.read(cbuf)); // 4
    System.out.println(Arrays.toString(cbuf)); // [a, b, c, d]
}

// An example without a try-with-resources statement.
final byte[] bytes = "abcd".getBytes();
final var reader = new InputStreamReader(new ByteArrayInputStream(bytes));
try {
    final var cbuf = new char[4];

    System.out.println(reader.read(cbuf)); // 4
    System.out.println(Arrays.toString(cbuf)); // [a, b, c, d]
} finally {
    reader.close();
}

String getEncoding ()

Returns the name of the character encoding being used by this stream.

final byte[] bytes = "abcd".getBytes();

try (final var reader = new InputStreamReader(
        new ByteArrayInputStream(bytes))) {
    final var ret = reader.getEncoding();
    System.out.println(ret); // UTF8
}

final var sjis = Charset.forName("Shift_JIS");
final byte[] bytes = "abcd".getBytes(sjis);

try (final var reader = new InputStreamReader(
        new ByteArrayInputStream(bytes), sjis)) {
    final var ret = reader.getEncoding();
    System.out.println(ret); // SJIS
}

int read ()

Reads a single character.

final byte[] bytes = "abc".getBytes();

try (final var reader = new InputStreamReader(new ByteArrayInputStream(bytes))) {
    final var ret1 = reader.read();
    System.out.printf("%d : %c%n", ret1, ret1); // 97 : a

    final var ret2 = reader.read();
    System.out.printf("%d : %c%n", ret2, ret2); // 98 : b

    final var ret3 = reader.read();
    System.out.printf("%d : %c%n", ret3, ret3); // 99 : c

    final var ret4 = reader.read();
    System.out.println(ret4); // -1
}

int read (char[] cbuf, int off, int len)

Reads characters into a portion of an array.

final byte[] bytes = "abcdefg".getBytes();

try (final var reader = new InputStreamReader(new ByteArrayInputStream(bytes))) {
    final var cbuf = new char[5];

    System.out.println(reader.read(cbuf, 0, 1)); // 1
    System.out.println(Arrays.toString(cbuf)); // [a,  ,  ,  ,  ]

    System.out.println(reader.read(cbuf, 0, 2)); // 2
    System.out.println(Arrays.toString(cbuf)); // [b, c,  ,  ,  ]

    System.out.println(reader.read(cbuf, 0, 3)); // 3
    System.out.println(Arrays.toString(cbuf)); // [d, e, f,  ,  ]

    System.out.println(reader.read(cbuf, 0, 4)); // 1
    System.out.println(Arrays.toString(cbuf)); // [g, e, f,  ,  ]

    System.out.println(reader.read(cbuf, 0, 5)); // -1
    System.out.println(Arrays.toString(cbuf)); // [g, e, f,  ,  ]
}

final byte[] bytes = "abcde".getBytes();

try (final var reader = new InputStreamReader(new ByteArrayInputStream(bytes))) {
    final var cbuf = new char[5];

    System.out.println(reader.read(cbuf, 4, 1)); // 1
    System.out.println(Arrays.toString(cbuf)); // [ ,  ,  ,  , a]

    System.out.println(reader.read(cbuf, 3, 1)); // 1
    System.out.println(Arrays.toString(cbuf)); // [ ,  ,  , b, a]

    System.out.println(reader.read(cbuf, 2, 1)); // 1
    System.out.println(Arrays.toString(cbuf)); // [ ,  , c, b, a]

    System.out.println(reader.read(cbuf, 1, 1)); // 1
    System.out.println(Arrays.toString(cbuf)); // [ , d, c, b, a]

    System.out.println(reader.read(cbuf, 0, 1)); // 1
    System.out.println(Arrays.toString(cbuf)); // [e, d, c, b, a]
}

final byte[] bytes = "abcdefg".getBytes();

try (final var reader = new InputStreamReader(new ByteArrayInputStream(bytes))) {
    final var cbuf = new char[3];

    System.out.println(reader.read(cbuf, 0, 3)); // 3
    System.out.println(Arrays.toString(cbuf)); // [a, b, c]

    //reader.read(cbuf, 0, 4); // IndexOutOfBoundsException
    //reader.read(cbuf, 3, 1); // IndexOutOfBoundsException
}

boolean ready ()

Tells whether this stream is ready to be read.

final byte[] bytes = "abc".getBytes();

try (final var reader = new InputStreamReader(new ByteArrayInputStream(bytes))) {
    System.out.println(reader.ready()); // true
    System.out.printf("%c%n", reader.read()); // a

    System.out.println(reader.ready()); // true
    System.out.printf("%c%n", reader.read()); // b

    System.out.println(reader.ready()); // true
    System.out.printf("%c%n", reader.read()); // c

    System.out.println(reader.ready()); // false
    System.out.println(reader.read()); // -1
}

Methods declared in Reader

mark, markSupported, nullReader, read, read, reset, skip, transferTo

Please see the link below.

Reader with Examples

API Examples

Java : InputStreamReader with Examples

Summary

Fields declared in Reader

lock

Constructors

InputStreamReader (InputStream in)

InputStreamReader (InputStream in, String charsetName)

InputStreamReader (InputStream in, Charset cs)

InputStreamReader (InputStream in, CharsetDecoder dec)

Methods

void close ()

String getEncoding ()

int read ()

int read (char[] cbuf, int off, int len)

boolean ready ()

Methods declared in Reader

mark, markSupported, nullReader, read, read, reset, skip, transferTo

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