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Java : InputStreamReader with Examples

Last Modified : August 10, 2024 Published : October 7, 2022

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.

InputStreamReader (Java SE 21 & JDK 21)

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.

Constructors

InputStreamReader (InputStream in)

Creates an InputStreamReader that uses the default charset.

InputStreamReader (Java SE 21 & JDK 21) 
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.

InputStreamReader (Java SE 21 & JDK 21) 
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.

InputStreamReader (Java SE 21 & JDK 21) 
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.

InputStreamReader (Java SE 21 & JDK 21) 
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.

InputStreamReader (Java SE 21 & JDK 21) 
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.

InputStreamReader (Java SE 21 & JDK 21) 
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.

InputStreamReader (Java SE 21 & JDK 21) 
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.

InputStreamReader (Java SE 21 & JDK 21) 
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.

InputStreamReader (Java SE 21 & JDK 21) 
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.


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