Java : InputStreamReader with Examples
Last Modified : July 15, 2023 Published : October 7, 2022
InputStreamReader (Java SE 18 & JDK 18) API 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.
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
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();
}
// Once the reader has been closed, read methods will throw an IOException.
try {
reader.read();
} catch (IOException e) {
System.out.println(e);
// Result
// ↓
//java.io.IOException: Stream closed
}
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.
Please see InputStreamReader(InputStream in).
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.
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