com.google.common.io.LineReader 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.io.CharStreams.createBuffer;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtIncompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.io.IOException;
import java.io.Reader;
import java.nio.CharBuffer;
import java.util.LinkedList;
import java.util.Queue;
import org.checkerframework.checker.nullness.compatqual.NullableDecl;
/**
* A class for reading lines of text. Provides the same functionality as {@link
* java.io.BufferedReader#readLine()} but for all {@link Readable} objects, not just instances of
* {@link Reader}.
*
* @author Chris Nokleberg
* @since 1.0
*/
@Beta
@GwtIncompatible
public final class LineReader {
private final Readable readable;
@NullableDecl private final Reader reader;
private final CharBuffer cbuf = createBuffer();
private final char[] buf = cbuf.array();
private final Queue lines = new LinkedList<>();
private final LineBuffer lineBuf =
new LineBuffer() {
@Override
protected void handleLine(String line, String end) {
lines.add(line);
}
};
/** Creates a new instance that will read lines from the given {@code Readable} object. */
public LineReader(Readable readable) {
this.readable = checkNotNull(readable);
this.reader = (readable instanceof Reader) ? (Reader) readable : null;
}
/**
* Reads a line of text. A line is considered to be terminated by any one of a line feed ({@code
* '\n'}), a carriage return ({@code '\r'}), or a carriage return followed immediately by a
* linefeed ({@code "\r\n"}).
*
* @return a {@code String} containing the contents of the line, not including any
* line-termination characters, or {@code null} if the end of the stream has been reached.
* @throws IOException if an I/O error occurs
*/
@CanIgnoreReturnValue // to skip a line
public String readLine() throws IOException {
while (lines.peek() == null) {
cbuf.clear();
// The default implementation of Reader#read(CharBuffer) allocates a
// temporary char[], so we call Reader#read(char[], int, int) instead.
int read = (reader != null) ? reader.read(buf, 0, buf.length) : readable.read(cbuf);
if (read == -1) {
lineBuf.finish();
break;
}
lineBuf.add(buf, 0, read);
}
return lines.poll();
}
}