https://github.com/farble1670/boundedlinereader
BufferedReader.readLine() cannot be hardened. There’s no way to restrict the number of characters read per line. If you cannot control the input to your reader, that’s a problem. Here’s a simple Reader implementation that can read lines, bounded by a maximum character length.
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
class BoundedLineReader extends InputStreamReader {
static final String NEWLINE = System.getProperty("line.separator");
private final char[] buffer;
public BoundedLineReader(InputStream in, int maxLineLength) {
super(in);
this.buffer = new char[maxLineLength];
}
public String readLine() throws IOException {
char[] last = new char[NEWLINE.length()];
int c;
int i = 0;
boolean nl = false;
while ((c = read()) != -1 && i < buffer.length) {
shiftIn(last, (char) c);
buffer[i++] = (char) c;
if (equals(NEWLINE, last)) {
nl = true;
break;
}
}
// chomp any newline or newline segment from end of buffer
for (int j = 0; j < NEWLINE.length() && i > 0; j++) {
if (buffer[i - 1] == '\n' || buffer[i - 1] == '\r') {
i--;
}
}
if (i == 0) {
return null;
}
String result = new String(buffer, 0, i);
if (!nl) {
// didn't read newline, consume until we read it
while ((c = read()) != -1) {
shiftIn(last, (char) c);
if (equals(NEWLINE, last)) {
break;
}
}
}
return result;
}
private boolean equals(String s, char[] a) {
if (a.length != s.length()) {
return false;
}
for (int i = 0; i < s.length(); i++) {
if (s.charAt(i) != a[i]) {
return false;
}
}
return true;
}
private void shiftIn(char[] a, char c) {
for (int i = a.length - 1; i >= 1; i--) {
a[i - 1] = a[i];
}
a[a.length - 1] = c;
}
public int skipLines(int num) {
int i = 0;
try {
while (readLine() != null && ++i <= num) {
}
} catch (IOException e) {
}
return i - 1;
}
}
This is not a buffered reader. It reads one character at a time making it inefficient and not suited for production. Here’s a better implementation that’s a copy of Java’s BufferedReader with a few modifications to the readLine() method,
/**
* This class is a copy of java.io.BufferedReader that can bound maximum line length when read using readLine(int).
*
* If the line length exceeds the passed length, the line up to the length is returned.
* Subsequent readLine(int) calls will return the next line with the same restrictions.
*
* This class also provides a skipLines(int) method that will skip past the given number of lines, or less
* if stream contains fewer lines.
*/
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.Reader;
/**
* Wraps an existing {@link Reader} and <em>buffers</em> the input. Expensive
* interaction with the underlying reader is minimized, since most (smaller)
* requests can be satisfied by accessing the buffer alone. The drawback is that
* some extra space is required to hold the buffer and that copying takes place
* when filling that buffer, but this is usually outweighed by the performance
* benefits.
* <p/>
* <p/>A typical application pattern for the class looks like this:<p/>
* <p/>
* <pre>
* BufferedReader buf = new BufferedReader(new FileReader("file.java"));
* </pre>
*
* @see BufferedWriter
* @since 1.1
*/
public class BoundedBufferedReader extends Reader {
private Reader in;
/**
* The characters that can be read and refilled in bulk. We maintain three
* indices into this buffer:<pre>
* { X X X X X X X X X X X X - - }
* ^ ^ ^
* | | |
* mark pos end</pre>
* Pos points to the next readable character. End is one greater than the
* last readable character. When {@code pos == end}, the buffer is empty and
* must be {@link #fillBuf() filled} before characters can be read.
* <p/>
* <p>Mark is the value pos will be set to on calls to {@link #reset}. Its
* value is in the range {@code [0...pos]}. If the mark is {@code -1}, the
* buffer cannot be reset.
* <p/>
* <p>MarkLimit limits the distance between the mark and the pos. When this
* limit is exceeded, {@link #reset} is permitted (but not required) to
* throw an exception. For shorter distances, {@link #reset} shall not throw
* (unless the reader is closed).
*/
private char[] buf;
private int pos;
private int end;
private int mark = -1;
private int markLimit = -1;
/**
* readLine returns a line as soon as it sees '\n' or '\r'. In the latter
* case, there might be a following '\n' that should be treated as part of
* the same line ending. Both readLine and all read methods are supposed
* to skip the '\n' (and clear this field) but only readLine looks for '\r'
* and sets it.
*/
private boolean lastWasCR;
/**
* We also need to keep the 'lastWasCR' state for the mark position, in case
* we reset to there.
*/
private boolean markedLastWasCR;
/**
* Constructs a new {@code BufferedReader}, providing {@code in} with a buffer
* of 8192 characters.
*
* @param in the {@code Reader} the buffer reads from.
*/
public BoundedBufferedReader(Reader in) {
this(in, 8192);
}
/**
* Constructs a new {@code BufferedReader}, providing {@code in} with {@code size} characters
* of buffer.
*
* @param in the {@code InputStream} the buffer reads from.
* @param size the size of buffer in characters.
* @throws IllegalArgumentException if {@code size <= 0}.
*/
public BoundedBufferedReader(Reader in, int size) {
super(in);
if (size <= 0) {
throw new IllegalArgumentException("size <= 0");
}
this.in = in;
buf = new char[size];
}
/**
* Closes this reader. This implementation closes the buffered source reader
* and releases the buffer. Nothing is done if this reader has already been
* closed.
*
* @throws IOException if an error occurs while closing this reader.
*/
@Override
public void close() throws IOException {
synchronized (lock) {
if (!isClosed()) {
in.close();
buf = null;
}
}
}
/**
* Populates the buffer with data. It is an error to call this method when
* the buffer still contains data; ie. if {@code pos < end}.
*
* @return the number of chars read into the buffer, or -1 if the end of the
* source stream has been reached.
*/
private int fillBuf() throws IOException {
// assert(pos == end);
if (mark == -1 || (pos - mark >= markLimit)) {
/* mark isn't set or has exceeded its limit. use the whole buffer */
int result = in.read(buf, 0, buf.length);
if (result > 0) {
mark = -1;
pos = 0;
end = result;
}
return result;
}
if (mark == 0 && markLimit > buf.length) {
/* the only way to make room when mark=0 is by growing the buffer */
int newLength = buf.length * 2;
if (newLength > markLimit) {
newLength = markLimit;
}
char[] newbuf = new char[newLength];
System.arraycopy(buf, 0, newbuf, 0, buf.length);
buf = newbuf;
} else if (mark > 0) {
/* make room by shifting the buffered data to left mark positions */
System.arraycopy(buf, mark, buf, 0, buf.length - mark);
pos -= mark;
end -= mark;
mark = 0;
}
/* Set the new position and mark position */
int count = in.read(buf, pos, buf.length - pos);
if (count != -1) {
end += count;
}
return count;
}
/**
* Indicates whether or not this reader is closed.
*
* @return {@code true} if this reader is closed, {@code false}
* otherwise.
*/
private boolean isClosed() {
return buf == null;
}
/**
* Sets a mark position in this reader. The parameter {@code markLimit}
* indicates how many characters can be read before the mark is invalidated.
* Calling {@code reset()} will reposition the reader back to the marked
* position if {@code markLimit} has not been surpassed.
*
* @param markLimit the number of characters that can be read before the mark is
* invalidated.
* @throws IllegalArgumentException if {@code markLimit < 0}.
* @throws IOException if an error occurs while setting a mark in this reader.
* @see #markSupported()
* @see #reset()
*/
@Override
public void mark(int markLimit) throws IOException {
if (markLimit < 0) {
throw new IllegalArgumentException("markLimit < 0:" + markLimit);
}
synchronized (lock) {
checkNotClosed();
this.markLimit = markLimit;
this.mark = pos;
this.markedLastWasCR = lastWasCR;
}
}
private void checkNotClosed() throws IOException {
if (isClosed()) {
throw new IOException("BufferedReader is closed");
}
}
/**
* Indicates whether this reader supports the {@code mark()} and
* {@code reset()} methods. This implementation returns {@code true}.
*
* @return {@code true} for {@code BufferedReader}.
* @see #mark(int)
* @see #reset()
*/
@Override
public boolean markSupported() {
return true;
}
/**
* Reads a single character from this reader and returns it with the two
* higher-order bytes set to 0. If possible, BufferedReader returns a
* character from the buffer. If there are no characters available in the
* buffer, it fills the buffer and then returns a character. It returns -1
* if there are no more characters in the source reader.
*
* @return the character read or -1 if the end of the source reader has been
* reached.
* @throws IOException if this reader is closed or some other I/O error occurs.
*/
@Override
public int read() throws IOException {
synchronized (lock) {
checkNotClosed();
int ch = readChar();
if (lastWasCR && ch == '\n') {
ch = readChar();
}
lastWasCR = false;
return ch;
}
}
private int readChar() throws IOException {
if (pos < end || fillBuf() != -1) {
return buf[pos++];
}
return -1;
}
/**
* Reads up to {@code length} characters from this reader and stores them
* at {@code offset} in the character array {@code buffer}. Returns the
* number of characters actually read or -1 if the end of the source reader
* has been reached. If all the buffered characters have been used, a mark
* has not been set and the requested number of characters is larger than
* this readers buffer size, BufferedReader bypasses the buffer and simply
* places the results directly into {@code buffer}.
*
* @throws IndexOutOfBoundsException if {@code offset < 0 || length < 0 || offset + length > buffer.length}.
* @throws IOException if this reader is closed or some other I/O error occurs.
*/
@Override
public int read(char[] buffer, int offset, int length) throws IOException {
synchronized (lock) {
checkNotClosed();
checkOffsetAndCount(buffer.length, offset, length);
if (length == 0) {
return 0;
}
maybeSwallowLF();
int outstanding = length;
while (outstanding > 0) {
// If there are chars in the buffer, grab those first.
int available = end - pos;
if (available > 0) {
int count = available >= outstanding ? outstanding : available;
System.arraycopy(buf, pos, buffer, offset, count);
pos += count;
offset += count;
outstanding -= count;
}
/*
* Before attempting to read from the underlying stream, make
* sure we really, really want to. We won't bother if we're
* done, or if we've already got some chars and reading from the
* underlying stream would block.
*/
if (outstanding == 0 || (outstanding < length && !in.ready())) {
break;
}
// assert(pos == end);
/*
* If we're unmarked and the requested size is greater than our
* buffer, read the chars directly into the caller's buffer. We
* don't read into smaller buffers because that could result in
* a many reads.
*/
if ((mark == -1 || (pos - mark >= markLimit)) && outstanding >= buf.length) {
int count = in.read(buffer, offset, outstanding);
if (count > 0) {
outstanding -= count;
mark = -1;
}
break; // assume the source stream gave us all that it could
}
if (fillBuf() == -1) {
break; // source is exhausted
}
}
int count = length - outstanding;
if (count > 0) {
return count;
}
return -1;
}
}
/**
* Peeks at the next input character, refilling the buffer if necessary. If
* this character is a newline character ("\n"), it is discarded.
*/
final void chompNewline() throws IOException {
if ((pos != end || fillBuf() != -1) && buf[pos] == '\n') {
++pos;
}
}
// If the last character was CR and the next character is LF, skip it.
private void maybeSwallowLF() throws IOException {
if (lastWasCR) {
chompNewline();
lastWasCR = false;
}
}
/**
* Returns the next line of text available from this reader. A line is
* represented by zero or more characters followed by {@code '\n'},
* {@code '\r'}, {@code "\r\n"} or the end of the reader. The string does
* not include the newline sequence.
*
* @param maxLen The maximum String length to return.
*
* @return the contents of the line or {@code null} if no characters were
* read before the end of the reader has been reached.
* @throws IOException if this reader is closed or some other I/O error occurs.
*/
public String readLine(int maxLen) throws IOException {
synchronized (lock) {
checkNotClosed();
maybeSwallowLF();
// Do we have a whole line in the buffer?
for (int i = pos; i < end; ++i) {
char ch = buf[i];
if (ch == '\n' || ch == '\r') {
String line = new String(buf, pos, Math.min(i - pos, maxLen));
pos = i + 1;
lastWasCR = (ch == '\r');
return line;
}
}
// Accumulate buffers in a StringBuilder until we've read a whole line.
StringBuilder result = new StringBuilder(end - pos + 80);
result.append(buf, pos, Math.min(end - pos, maxLen - result.length()));
while (true) {
pos = end;
if (fillBuf() == -1) {
// If there's no more input, return what we've read so far, if anything.
return (result.length() > 0) ? result.toString() : null;
}
// Do we have a whole line in the buffer now?
for (int i = pos; i < end; ++i) {
char ch = buf[i];
if (ch == '\n' || ch == '\r') {
result.append(buf, pos, Math.min(i - pos, maxLen - result.length()));
pos = i + 1;
lastWasCR = (ch == '\r');
return result.toString();
}
}
// Add this whole buffer to the line-in-progress and try again...
result.append(buf, pos, Math.min(end - pos, maxLen - result.length()));
}
}
}
/**
* Indicates whether this reader is ready to be read without blocking.
*
* @return {@code true} if this reader will not block when {@code read} is
* called, {@code false} if unknown or blocking will occur.
* @throws IOException if this reader is closed or some other I/O error occurs.
* @see #read()
* @see #read(char[], int, int)
* @see #readLine()
*/
@Override
public boolean ready() throws IOException {
synchronized (lock) {
checkNotClosed();
return ((end - pos) > 0) || in.ready();
}
}
/**
* Resets this reader's position to the last {@code mark()} location.
* Invocations of {@code read()} and {@code skip()} will occur from this new
* location.
*
* @throws IOException if this reader is closed or no mark has been set.
* @see #mark(int)
* @see #markSupported()
*/
@Override
public void reset() throws IOException {
synchronized (lock) {
checkNotClosed();
if (mark == -1) {
throw new IOException("Invalid mark");
}
this.pos = mark;
this.lastWasCR = this.markedLastWasCR;
}
}
/**
* Skips at most {@code charCount} chars in this stream. Subsequent calls to
* {@code read} will not return these chars unless {@code reset} is
* used.
* <p/>
* <p>Skipping characters may invalidate a mark if {@code markLimit}
* is surpassed.
*
* @return the number of characters actually skipped.
* @throws IllegalArgumentException if {@code charCount < 0}.
* @throws IOException if this reader is closed or some other I/O error occurs.
*/
@Override
public long skip(long charCount) throws IOException {
if (charCount < 0) {
throw new IllegalArgumentException("charCount < 0: " + charCount);
}
synchronized (lock) {
checkNotClosed();
if (end - pos >= charCount) {
pos += charCount;
return charCount;
}
long read = end - pos;
pos = end;
while (read < charCount) {
if (fillBuf() == -1) {
return read;
}
if (end - pos >= charCount - read) {
pos += charCount - read;
return charCount;
}
// Couldn't get all the characters, skip what we read
read += (end - pos);
pos = end;
}
return charCount;
}
}
private static void checkOffsetAndCount(int arrayLength, int offset, int count) {
if ((offset | count) < 0 || offset > arrayLength || arrayLength - offset < count) {
throw new ArrayIndexOutOfBoundsException(String.format("length: %s, offset: %d, count: %d", arrayLength, offset, count));
}
}
/**
* Skip (read past) the given number of lines.
*/
public int skipLines(int num) {
if (num == 0) {
return 0;
}
int i = 0;
try {
while (readLine(0) != null) {
if (++i >= num) {
break;
}
}
} catch (IOException e) {
}
return i;
}
}
Posted by Jeffrey Blattman 
Zero Credibility 