With this example we are going to demonstrate how to count the frequency of words in a file. In short, to count the frequency of words in a file you should:
- Create a new FileInputStream with a given String path by opening a connection to a file.
- Get the FileChannel object associated with the FileInputStream, with
getChannel()API method of FileInputStream. - Get the current size of this channel’s file, using
size()API method of FileChannel. - Create a MappedByteBuffer, using
map(MapMode mode, long position, long size)API method of FileChannel that maps a region of this channel’s file directly into memory. - Convert the byte buffer to character buffer. Create a new Charset for a specified charset name, using
forName(String charsetName)API method of Charset and then a new CharsetDecoder, usingnewDecoder()API method of Charset. Then usedecode(ByteBuffer in)API method of CharBuffer to decode the remaining content of a single input byte buffer into a newly-allocated character buffer. - Create a new word pattern and a new line pattern, by compiling given String regular expressions to a Pattern, using
compile(string regex)API method of Pattern. - Match the line pattern to the buffer, using
matcher(CharSequence input)API method of Pattern. - For each line get the line and the array of words in the line, using
find()andgroup()API methods of Matcher, for the matcher created for the line pattern. - Then for each word get the word and add it in a TreeMap.
Let’s take a look at the code snippet that follows:
package com.javacodegeeks.snippets.core;
import java.io.FileInputStream;
import java.nio.CharBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.util.Map;
import java.util.TreeMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class WordFreq {
public static void main(String args[]) throws Exception {
String filePath = "C:/Users/nikos7/Desktop/file.odt";
// Map File from filename to byte buffer
FileInputStream in = new FileInputStream(filePath);
FileChannel filech = in.getChannel();
int fileLen = (int) filech.size();
MappedByteBuffer buf = filech.map(FileChannel.MapMode.READ_ONLY, 0,
fileLen);
// Convert to character buffer
Charset chars = Charset.forName("ISO-8859-1");
CharsetDecoder dec = chars.newDecoder();
CharBuffer charBuf = dec.decode(buf);
// Create line pattern
Pattern linePatt = Pattern.compile(".*$", Pattern.MULTILINE);
// Create word pattern
Pattern wordBrkPatt = Pattern.compile("[\\p{Punct}\s}]");
// Match line pattern to buffer
Matcher lineM = linePatt.matcher(charBuf);
Map m = new TreeMap();
Integer one = new Integer(1);
// For each line
while (lineM.find()) {
// Get line
CharSequence lineSeq = lineM.group();
// Get array of words on line
String words[] = wordBrkPatt.split(lineSeq);
// For each word
for (int i = 0, n = words.length; i < n; i++) {
if (words[i].length() > 0) {
Integer frequency = (Integer) m.get(words[i]);
if (frequency == null) {
frequency = one;
} else {
int value = frequency.intValue();
frequency = new Integer(value + 1);
}
m.put(words[i], frequency);
}
}
}
System.out.println(m);
}
}
Output:
WordPress=2, Working=1, Your=3, You’ll=1, a=136, able=1, about=8, above=2, absolutely=1, absurd=1, accept=.....
This was an example of how to count the frequency of words in a file in Java.
