com.google.common.io.CharStreams Maven / Gradle / Ivy
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/*
* Copyright (C) 2007 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
* in compliance with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the License
* is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
* or implied. See the License for the specific language governing permissions and limitations under
* the License.
*/
package com.google.common.io;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkPositionIndexes;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtIncompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.Closeable;
import java.io.EOFException;
import java.io.IOException;
import java.io.Reader;
import java.io.Writer;
import java.nio.CharBuffer;
import java.util.ArrayList;
import java.util.List;
import org.checkerframework.checker.nullness.qual.Nullable;
/**
* Provides utility methods for working with character streams.
*
* All method parameters must be non-null unless documented otherwise.
*
*
Some of the methods in this class take arguments with a generic type of {@code Readable &
* Closeable}. A {@link java.io.Reader} implements both of those interfaces. Similarly for {@code
* Appendable & Closeable} and {@link java.io.Writer}.
*
* @author Chris Nokleberg
* @author Bin Zhu
* @author Colin Decker
* @since 1.0
*/
@GwtIncompatible
public final class CharStreams {
// 2K chars (4K bytes)
private static final int DEFAULT_BUF_SIZE = 0x800;
/** Creates a new {@code CharBuffer} for buffering reads or writes. */
static CharBuffer createBuffer() {
return CharBuffer.allocate(DEFAULT_BUF_SIZE);
}
private CharStreams() {}
/**
* Copies all characters between the {@link Readable} and {@link Appendable} objects. Does not
* close or flush either object.
*
* @param from the object to read from
* @param to the object to write to
* @return the number of characters copied
* @throws IOException if an I/O error occurs
*/
@CanIgnoreReturnValue
public static long copy(Readable from, Appendable to) throws IOException {
// The most common case is that from is a Reader (like InputStreamReader or StringReader) so
// take advantage of that.
if (from instanceof Reader) {
// optimize for common output types which are optimized to deal with char[]
if (to instanceof StringBuilder) {
return copyReaderToBuilder((Reader) from, (StringBuilder) to);
} else {
return copyReaderToWriter((Reader) from, asWriter(to));
}
} else {
checkNotNull(from);
checkNotNull(to);
long total = 0;
CharBuffer buf = createBuffer();
while (from.read(buf) != -1) {
buf.flip();
to.append(buf);
total += buf.remaining();
buf.clear();
}
return total;
}
}
// TODO(lukes): consider allowing callers to pass in a buffer to use, some callers would be able
// to reuse buffers, others would be able to size them more appropriately than the constant
// defaults
/**
* Copies all characters between the {@link Reader} and {@link StringBuilder} objects. Does not
* close or flush the reader.
*
*
This is identical to {@link #copy(Readable, Appendable)} but optimized for these specific
* types. CharBuffer has poor performance when being written into or read out of so round tripping
* all the bytes through the buffer takes a long time. With these specialized types we can just
* use a char array.
*
* @param from the object to read from
* @param to the object to write to
* @return the number of characters copied
* @throws IOException if an I/O error occurs
*/
@CanIgnoreReturnValue
static long copyReaderToBuilder(Reader from, StringBuilder to) throws IOException {
checkNotNull(from);
checkNotNull(to);
char[] buf = new char[DEFAULT_BUF_SIZE];
int nRead;
long total = 0;
while ((nRead = from.read(buf)) != -1) {
to.append(buf, 0, nRead);
total += nRead;
}
return total;
}
/**
* Copies all characters between the {@link Reader} and {@link Writer} objects. Does not close or
* flush the reader or writer.
*
*
This is identical to {@link #copy(Readable, Appendable)} but optimized for these specific
* types. CharBuffer has poor performance when being written into or read out of so round tripping
* all the bytes through the buffer takes a long time. With these specialized types we can just
* use a char array.
*
* @param from the object to read from
* @param to the object to write to
* @return the number of characters copied
* @throws IOException if an I/O error occurs
*/
@CanIgnoreReturnValue
static long copyReaderToWriter(Reader from, Writer to) throws IOException {
checkNotNull(from);
checkNotNull(to);
char[] buf = new char[DEFAULT_BUF_SIZE];
int nRead;
long total = 0;
while ((nRead = from.read(buf)) != -1) {
to.write(buf, 0, nRead);
total += nRead;
}
return total;
}
/**
* Reads all characters from a {@link Readable} object into a {@link String}. Does not close the
* {@code Readable}.
*
* @param r the object to read from
* @return a string containing all the characters
* @throws IOException if an I/O error occurs
*/
public static String toString(Readable r) throws IOException {
return toStringBuilder(r).toString();
}
/**
* Reads all characters from a {@link Readable} object into a new {@link StringBuilder} instance.
* Does not close the {@code Readable}.
*
* @param r the object to read from
* @return a {@link StringBuilder} containing all the characters
* @throws IOException if an I/O error occurs
*/
private static StringBuilder toStringBuilder(Readable r) throws IOException {
StringBuilder sb = new StringBuilder();
if (r instanceof Reader) {
copyReaderToBuilder((Reader) r, sb);
} else {
copy(r, sb);
}
return sb;
}
/**
* Reads all of the lines from a {@link Readable} object. The lines do not include
* line-termination characters, but do include other leading and trailing whitespace.
*
*
Does not close the {@code Readable}. If reading files or resources you should use the {@link
* Files#readLines} and {@link Resources#readLines} methods.
*
* @param r the object to read from
* @return a mutable {@link List} containing all the lines
* @throws IOException if an I/O error occurs
*/
@Beta
public static List readLines(Readable r) throws IOException {
List result = new ArrayList<>();
LineReader lineReader = new LineReader(r);
String line;
while ((line = lineReader.readLine()) != null) {
result.add(line);
}
return result;
}
/**
* Streams lines from a {@link Readable} object, stopping when the processor returns {@code false}
* or all lines have been read and returning the result produced by the processor. Does not close
* {@code readable}. Note that this method may not fully consume the contents of {@code readable}
* if the processor stops processing early.
*
* @throws IOException if an I/O error occurs
* @since 14.0
*/
@Beta
@CanIgnoreReturnValue // some processors won't return a useful result
public static T readLines(Readable readable, LineProcessor processor) throws IOException {
checkNotNull(readable);
checkNotNull(processor);
LineReader lineReader = new LineReader(readable);
String line;
while ((line = lineReader.readLine()) != null) {
if (!processor.processLine(line)) {
break;
}
}
return processor.getResult();
}
/**
* Reads and discards data from the given {@code Readable} until the end of the stream is reached.
* Returns the total number of chars read. Does not close the stream.
*
* @since 20.0
*/
@Beta
@CanIgnoreReturnValue
public static long exhaust(Readable readable) throws IOException {
long total = 0;
long read;
CharBuffer buf = createBuffer();
while ((read = readable.read(buf)) != -1) {
total += read;
buf.clear();
}
return total;
}
/**
* Discards {@code n} characters of data from the reader. This method will block until the full
* amount has been skipped. Does not close the reader.
*
* @param reader the reader to read from
* @param n the number of characters to skip
* @throws EOFException if this stream reaches the end before skipping all the characters
* @throws IOException if an I/O error occurs
*/
@Beta
public static void skipFully(Reader reader, long n) throws IOException {
checkNotNull(reader);
while (n > 0) {
long amt = reader.skip(n);
if (amt == 0) {
throw new EOFException();
}
n -= amt;
}
}
/**
* Returns a {@link Writer} that simply discards written chars.
*
* @since 15.0
*/
@Beta
public static Writer nullWriter() {
return NullWriter.INSTANCE;
}
private static final class NullWriter extends Writer {
private static final NullWriter INSTANCE = new NullWriter();
@Override
public void write(int c) {}
@Override
public void write(char[] cbuf) {
checkNotNull(cbuf);
}
@Override
public void write(char[] cbuf, int off, int len) {
checkPositionIndexes(off, off + len, cbuf.length);
}
@Override
public void write(String str) {
checkNotNull(str);
}
@Override
public void write(String str, int off, int len) {
checkPositionIndexes(off, off + len, str.length());
}
@Override
public Writer append(@Nullable CharSequence csq) {
return this;
}
@Override
public Writer append(@Nullable CharSequence csq, int start, int end) {
checkPositionIndexes(start, end, csq == null ? "null".length() : csq.length());
return this;
}
@Override
public Writer append(char c) {
return this;
}
@Override
public void flush() {}
@Override
public void close() {}
@Override
public String toString() {
return "CharStreams.nullWriter()";
}
}
/**
* Returns a Writer that sends all output to the given {@link Appendable} target. Closing the
* writer will close the target if it is {@link Closeable}, and flushing the writer will flush the
* target if it is {@link java.io.Flushable}.
*
* @param target the object to which output will be sent
* @return a new Writer object, unless target is a Writer, in which case the target is returned
*/
@Beta
public static Writer asWriter(Appendable target) {
if (target instanceof Writer) {
return (Writer) target;
}
return new AppendableWriter(target);
}
}