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Processing Large Files in Java, Variation 7
package com.example.readFile.readFileJava;
import java.io.BufferedReader;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.time.Duration;
import java.time.Instant;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.regex.Pattern;
import static java.util.stream.Collectors.counting;
import static java.util.stream.Collectors.groupingBy;
public class ReadFileJavaApplicationBufferedReader7 {
static final String FILENAME = "itcont.txt";
// returns the time between startTime and now in milliseconds
static long between(Instant startTime) {
return Duration.between(startTime, Instant.now()).toMillis();
}
public static void main(String[] args) throws IOException {
Instant startTime = Instant.now();
try (BufferedReader b = Files.newBufferedReader(Path.of(FILENAME))) {
int[] indexes = {0, 432, 43243};
List<String> names = new ArrayList<>();
List<String> dates = new ArrayList<>();
List<String> firstNames = new ArrayList<>();
var namePat = Pattern.compile(", \\s*([^, ]+)");
char[] chars = new char[6];
StringBuilder sb = new StringBuilder(7);
System.out.println("Reading file using " + Caller.getName());
String readLine;
while ((readLine = b.readLine()) != null) {
// get all the names
String array1[] = readLine.split("\\|", 9);
String name = array1[7].strip();
names.add(name);
// extract first names
var matcher = namePat.matcher(name);
if (matcher.find()) {
firstNames.add(matcher.group(1));
}
// extract dates
String rawDate = array1[4].strip();
rawDate.getChars(0, 6, chars, 0);
sb.setLength(0);
sb.append(chars, 0, 4)
.append('-')
.append(chars, 4, 2);
dates.add(sb.toString());
}
for (int i : indexes) {
System.out.println("Name: " + names.get(i) + " at index: " + i);
}
System.out.println("Name time: " + between(startTime) + "ms");
System.out.println("Total file line count: " + names.size());
System.out.println("Line count time: " + between(startTime) + "ms");
Map<String, Long> dateMap = dates.stream()
.collect(groupingBy(date -> date, counting()));
dateMap.forEach((date, count)
-> System.out.println("Donations per month and year: " + date + " and donation count: " + count));
System.out.println("Donations time: " + between(startTime) + "ms");
Map<String, Long> nameMap = firstNames.stream()
.collect(groupingBy(name -> name, counting()));
Entry<String, Long> common = Collections.max(nameMap.entrySet(), Entry.comparingByValue());
System.out.println("The most common first name is: " + common.getKey() + " and it occurs: " + common.getValue() + " times.");
System.out.println("Most common name time: " + between(startTime) + "ms");
}
}
}
class Caller {
// gets the simple name of the caller's class
public static String getName() {
return StackWalker.getInstance()
.walk(s -> s.skip(1)
.findFirst()
.map(StackWalker.StackFrame::getClassName)
.map(name -> name.replaceFirst("^.*\\.", ""))
.orElse(""));
}
}
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