com.google.common.io.CharStreams Maven / Gradle / Ivy
/*
* 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 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;
/**
* 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
*/
@Beta
public final class CharStreams {
private static final int BUF_SIZE = 0x800; // 2K chars (4K bytes)
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
*/
public static long copy(Readable from, Appendable to) throws IOException {
checkNotNull(from);
checkNotNull(to);
CharBuffer buf = CharBuffer.allocate(BUF_SIZE);
long total = 0;
while (from.read(buf) != -1) {
buf.flip();
to.append(buf);
total += buf.remaining();
buf.clear();
}
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();
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
*/
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
*/
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();
}
/**
* 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
*/
public static void skipFully(Reader reader, long n) throws IOException {
checkNotNull(reader);
while (n > 0) {
long amt = reader.skip(n);
if (amt == 0) {
// force a blocking read
if (reader.read() == -1) {
throw new EOFException();
}
n--;
} else {
n -= amt;
}
}
}
/**
* Returns a {@link Writer} that simply discards written chars.
*
* @since 15.0
*/
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(CharSequence csq) {
checkNotNull(csq);
return this;
}
@Override
public Writer append(CharSequence csq, int start, int end) {
checkPositionIndexes(start, end, 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
*/
public static Writer asWriter(Appendable target) {
if (target instanceof Writer) {
return (Writer) target;
}
return new AppendableWriter(target);
}
// TODO(user): Remove these once Input/OutputSupplier methods are removed
static Reader asReader(final Readable readable) {
checkNotNull(readable);
if (readable instanceof Reader) {
return (Reader) readable;
}
return new Reader() {
@Override
public int read(char[] cbuf, int off, int len) throws IOException {
return read(CharBuffer.wrap(cbuf, off, len));
}
@Override
public int read(CharBuffer target) throws IOException {
return readable.read(target);
}
@Override
public void close() throws IOException {
if (readable instanceof Closeable) {
((Closeable) readable).close();
}
}
};
}
}