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 com.google.common.annotations.Beta;
import com.google.common.base.Charsets;
import com.google.common.base.Preconditions;
import java.io.Closeable;
import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Reader;
import java.io.StringReader;
import java.io.Writer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.Arrays;
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
* @since 1.0
*/
@Beta
public final class CharStreams {
private static final int BUF_SIZE = 0x800; // 2K chars (4K bytes)
private CharStreams() {}
/**
* Returns a factory that will supply instances of {@link StringReader} that
* read a string value.
*
* @param value the string to read
* @return the factory
*/
public static InputSupplier newReaderSupplier(
final String value) {
Preconditions.checkNotNull(value);
return new InputSupplier() {
@Override
public StringReader getInput() {
return new StringReader(value);
}
};
}
/**
* Returns a factory that will supply instances of {@link InputStreamReader},
* using the given {@link InputStream} factory and character set.
*
* @param in the factory that will be used to open input streams
* @param charset the charset used to decode the input stream; see {@link
* Charsets} for helpful predefined constants
* @return the factory
*/
public static InputSupplier newReaderSupplier(
final InputSupplier in, final Charset charset) {
Preconditions.checkNotNull(in);
Preconditions.checkNotNull(charset);
return new InputSupplier() {
@Override
public InputStreamReader getInput() throws IOException {
return new InputStreamReader(in.getInput(), charset);
}
};
}
/**
* Returns a factory that will supply instances of {@link OutputStreamWriter},
* using the given {@link OutputStream} factory and character set.
*
* @param out the factory that will be used to open output streams
* @param charset the charset used to encode the output stream; see {@link
* Charsets} for helpful predefined constants
* @return the factory
*/
public static OutputSupplier newWriterSupplier(
final OutputSupplier out, final Charset charset) {
Preconditions.checkNotNull(out);
Preconditions.checkNotNull(charset);
return new OutputSupplier() {
@Override
public OutputStreamWriter getOutput() throws IOException {
return new OutputStreamWriter(out.getOutput(), charset);
}
};
}
/**
* Writes a character sequence (such as a string) to an appendable
* object from the given supplier.
*
* @param from the character sequence to write
* @param to the output supplier
* @throws IOException if an I/O error occurs
*/
public static void write(CharSequence from,
OutputSupplier to) throws IOException {
Preconditions.checkNotNull(from);
boolean threw = true;
W out = to.getOutput();
try {
out.append(from);
threw = false;
} finally {
Closeables.close(out, threw);
}
}
/**
* Opens {@link Readable} and {@link Appendable} objects from the
* given factories, copies all characters between the two, and closes
* them.
*
* @param from the input factory
* @param to the output factory
* @return the number of characters copied
* @throws IOException if an I/O error occurs
*/
public static long copy(InputSupplier from,
OutputSupplier to) throws IOException {
int successfulOps = 0;
R in = from.getInput();
try {
W out = to.getOutput();
try {
long count = copy(in, out);
successfulOps++;
return count;
} finally {
Closeables.close(out, successfulOps < 1);
successfulOps++;
}
} finally {
Closeables.close(in, successfulOps < 2);
}
}
/**
* Opens a {@link Readable} object from the supplier, copies all characters
* to the {@link Appendable} object, and closes the input. Does not close
* or flush the output.
*
* @param from the input factory
* @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(
InputSupplier from, Appendable to) throws IOException {
boolean threw = true;
R in = from.getInput();
try {
long count = copy(in, to);
threw = false;
return count;
} finally {
Closeables.close(in, threw);
}
}
/**
* 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 {
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();
}
/**
* Returns the characters from a {@link Readable} & {@link Closeable} object
* supplied by a factory as a {@link String}.
*
* @param supplier the factory to read from
* @return a string containing all the characters
* @throws IOException if an I/O error occurs
*/
public static String toString(
InputSupplier supplier) throws IOException {
return toStringBuilder(supplier).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;
}
/**
* Returns the characters from a {@link Readable} & {@link Closeable} object
* supplied by a factory as a new {@link StringBuilder} instance.
*
* @param supplier the factory to read from
* @throws IOException if an I/O error occurs
*/
private static StringBuilder toStringBuilder(
InputSupplier supplier) throws IOException {
boolean threw = true;
R r = supplier.getInput();
try {
StringBuilder result = toStringBuilder(r);
threw = false;
return result;
} finally {
Closeables.close(r, threw);
}
}
/**
* Reads the first line from a {@link Readable} & {@link Closeable} object
* supplied by a factory. The line does not include line-termination
* characters, but does include other leading and trailing whitespace.
*
* @param supplier the factory to read from
* @return the first line, or null if the reader is empty
* @throws IOException if an I/O error occurs
*/
public static String readFirstLine(
InputSupplier supplier) throws IOException {
boolean threw = true;
R r = supplier.getInput();
try {
String line = new LineReader(r).readLine();
threw = false;
return line;
} finally {
Closeables.close(r, threw);
}
}
/**
* Reads all of the lines from a {@link Readable} & {@link Closeable} object
* supplied by a factory. The lines do not include line-termination
* characters, but do include other leading and trailing whitespace.
*
* @param supplier the factory to read from
* @return a mutable {@link List} containing all the lines
* @throws IOException if an I/O error occurs
*/
public static List readLines(
InputSupplier supplier) throws IOException {
boolean threw = true;
R r = supplier.getInput();
try {
List result = readLines(r);
threw = false;
return result;
} finally {
Closeables.close(r, threw);
}
}
/**
* 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} and {@link Closeable} object
* supplied by a factory, stopping when our callback returns false, or we
* have read all of the lines.
*
* @param supplier the factory to read from
* @param callback the LineProcessor to use to handle the lines
* @return the output of processing the lines
* @throws IOException if an I/O error occurs
*/
public static T readLines(
InputSupplier supplier, LineProcessor callback) throws IOException {
boolean threw = true;
R r = supplier.getInput();
try {
LineReader lineReader = new LineReader(r);
String line;
while ((line = lineReader.readLine()) != null) {
if (!callback.processLine(line)) {
break;
}
}
threw = false;
} finally {
Closeables.close(r, threw);
}
return callback.getResult();
}
/**
* Joins multiple {@link Reader} suppliers into a single supplier.
* Reader returned from the supplier will contain the concatenated data
* from the readers of the underlying suppliers.
*
* Reading from the joined reader will throw a {@link NullPointerException}
* if any of the suppliers are null or return null.
*
*
Only one underlying reader will be open at a time. Closing the
* joined reader will close the open underlying reader.
*
* @param suppliers the suppliers to concatenate
* @return a supplier that will return a reader containing the concatenated
* data
*/
public static InputSupplier join(
final Iterable> suppliers) {
return new InputSupplier() {
@Override public Reader getInput() throws IOException {
return new MultiReader(suppliers.iterator());
}
};
}
/** Varargs form of {@link #join(Iterable)}. */
public static InputSupplier join(
InputSupplier... suppliers) {
return join(Arrays.asList(suppliers));
}
/**
* 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 bytes
* @throws IOException if an I/O error occurs
*/
public static void skipFully(Reader reader, long n) throws IOException {
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 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);
}
}