+import java.io.BufferedReader;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.StringReader;
+
+/**
+ * A file reader that concatenates lines
+ *
+ * @author gmcarstairs
+ *
+ */
+public class BufferedLineReader
+{
+ interface LineCleaner
+ {
+ String cleanLine(String l);
+ }
+
+ /*
+ * a reader for the file being read
+ */
+ private BufferedReader br;
+
+ /*
+ * optional handler to post-process each line as it is read
+ */
+ private LineCleaner cleaner;
+
+ /*
+ * current buffer of <bufferSize> post-processed input lines
+ */
+ private String[] buffer;
+
+ private boolean atEof;
+
+ /**
+ * Constructor
+ *
+ * @param reader
+ * @param bufferSize
+ * the number of lines to concatenate at a time while reading
+ * @param tidier
+ * an optional callback handler to post-process each line after
+ * reading
+ * @throws FileNotFoundException
+ */
+ public BufferedLineReader(BufferedReader reader, int bufferSize,
+ LineCleaner tidier)
+ throws IOException
+ {
+ br = reader;
+ buffer = new String[bufferSize];
+ cleaner = tidier;
+
+ /*
+ * load up the buffer with N-1 lines, ready for the first read
+ */
+ for (int i = 1; i < bufferSize; i++)
+ {
+ readLine();
+ }
+
+ }
+
+ /**
+ * Reads the next line from file, invokes the post-processor if one was
+ * provided, and returns the 'cleaned' line, or null at end of file.
+ *
+ * @return
+ */
+ private String readLine() // throws IOException
+ {
+ if (atEof)
+ {
+ return null;
+ }
+
+ String line = null;
+ try
+ {
+ line = br.readLine();
+ } catch (IOException e)
+ {
+ e.printStackTrace();
+ }
+ if (line == null)
+ {
+ atEof = true;
+ return null;
+ }
+ if (cleaner != null)
+ {
+ line = cleaner.cleanLine(line);
+ }
+
+ /*
+ * shuffle down the lines buffer and add the new line
+ * in the last position
+ */
+ for (int i = 1; i < buffer.length; i++)
+ {
+ buffer[i - 1] = buffer[i];
+ }
+ buffer[buffer.length - 1] = line;
+ return line;
+ }
+
+ /**
+ * Returns a number of concatenated lines from the file, or null at end of
+ * file.
+ *
+ * @return
+ */
+ public String read()
+ {
+ if (readLine() == null)
+ {
+ return null;
+ }
+ StringBuilder result = new StringBuilder(100 * buffer.length);
+ for (String line : buffer)
+ {
+ if (line != null)
+ {
+ result.append(line);
+ }
+ }
+ return result.toString();
+ }
+
+ /**
+ * A main 'test' method!
+ *
+ * @throws IOException
+ */
+ public static void main(String[] args) throws IOException
+ {
+ String data = "Now is the winter\n" + "Of our discontent\n"
+ + "Made glorious summer\n" + "By this sun of York\n";
+ BufferedReader br = new BufferedReader(new StringReader(data));
+ BufferedLineReader reader = new BufferedLineReader(br, 3,
+ new LineCleaner()
+ {
+ @Override
+ public String cleanLine(String l)
+ {
+ return l.toUpperCase();
+ }
+ });
+ String line = reader.read();
+ String expect = "NOW IS THE WINTEROF OUR DISCONTENTMADE GLORIOUS SUMMER";
+ if (!line.equals(expect))
+ {
+ System.err.println("Fail: expected '" + expect + "', found '" + line
+ + ";");
+ }
+ else
+ {
+ System.out.println("Line one ok!");
+ }
+ line = reader.read();
+ expect = "OF OUR DISCONTENTMADE GLORIOUS SUMMERBY THIS SUN OF YORK";
+ if (!line.equals(expect))
+ {
+ System.err.println("Fail: expected '" + expect + "', found '" + line
+ + "'");
+ }
+ else
+ {
+ System.out.println("Line two ok!!");
+ }
+ line = reader.read();
+ if (line != null)
+ {
+ System.err.println("Fail: expected null at eof, got '" + line + "'");
+ }
+ else
+ {
+ System.out.println("EOF ok!!!");
+ }
+ }
+}