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Busque en un archivo una Cadena y devuelva esa Cadena si la encuentra

Question

¿Cómo se puede buscar a través de un archivo txt una cadena que el usuario ingresa y luego devolver esa cadena a la consola? He escrito un código que no funciona a continuación, pero espero que pueda ilustrar mi punto ...

public static void main(String[] args) {
searchforName();
}
private static void searchForName() throws FileNotFoundException {
File file = new File("leaders.txt");
Scanner kb = new Scanner(System.in);
Scanner input = new Scanner(file);
System.out.println("Please enter the name you would like to search for: ");
String name = kb.nextLine();
while(input.hasNextLine()) {
System.out.println(input.next(name));
}
}

El archivo "leaders.txt" contiene una lista de nombres.

Answer 1

El escáner es demasiado lento. Ejecute el siguiente código y vea las diferencias. Se buscó en un archivo de 750 MB y BufferedReader es 10 veces más rápido que el escáner en promedio.

package uk.co.planetbeyond.service.test;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.Date;
import java.util.HashSet;
import java.util.Scanner;
public class SearchTextInFile
{
public static void main(String[] args) throws IOException
{
// First write a file, with large number of entries
writeFile("/home/aqeel/temp/subscribers_files.csv");
long scannerSearchMillis = 0;
long brSearchMillis = 0;
int iterations = 5;
// Now search random strings five times, and see the time taken
for (int i = 0; i < iterations; i++)
{
String msisdn = String.valueOf(923000000000l + ((long) (Math.random() * 40000000)));
System.out.println("ITERATION " + i);
System.out.print("Search " + msisdn + " using scanner");
Date d1 = new Date();
searchUsingScanner("/home/aqeel/temp/subscribers_files.csv", msisdn);
Date d2 = new Date();
long millis = (d2.getTime() - d1.getTime());
scannerSearchMillis += millis;
System.out.println(" | " + (millis / 1000) + " Seconds");
System.out.println("==================================================================");
System.out.print("Search " + msisdn + " using buffered reader");
d1 = new Date();
searchUsingBufferedReader("/home/aqeel/temp/subscribers_files.csv", msisdn);
d2 = new Date();
millis = d2.getTime() - d1.getTime();
brSearchMillis += millis;
System.out.println(" | " + (millis / 1000) + " Seconds");
System.out.println("==================================================================");
System.out.println("==================================================================");
System.out.println("==================================================================");
System.out.println("==================================================================");
}
System.out.println("Average Search time using Scanner " + (scannerSearchMillis / (iterations * 1000.0)) + " Seconds");
System.out.println("Average Search time using BufferedReader " + (brSearchMillis / (iterations * 1000.0)) + " Seconds");
}
public static void writeFile(String path)
{
BufferedWriter csvWriter = null;
HashSet<Integer> additions = new HashSet<Integer>();
try
{
csvWriter = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(path)));
for (int i = 0; i < 40000000; i++)
{
int addition = (int) (Math.random() * 40000000);
additions.add(addition);
if (i % 20000 == 0)
{
System.out.println("Entries written : " + i + " ------ Unique Entries: " + additions.size());
csvWriter.flush();
}
long msisdn = 923000000000l + addition;
csvWriter.write(String.valueOf(msisdn) + "|" + String.valueOf((int) (Math.random() * 131)) + "/r/n");
}
csvWriter.flush();
System.out.println("Unique Entries written : " + additions.size());
}
catch (Exception e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
finally
{
if (csvWriter != null)
{
try
{
csvWriter.close();
}
catch (IOException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
public static String searchUsingScanner(String filePath, String searchQuery) throws FileNotFoundException
{
searchQuery = searchQuery.trim();
Scanner scanner = null;
try
{
scanner = new Scanner(new File(filePath));
while (scanner.hasNextLine())
{
String line = scanner.nextLine();
if (line.contains(searchQuery))
{
return line;
}
else
{
}
}
}
finally
{
try
{
if (scanner != null)
scanner.close();
}
catch (Exception e)
{
System.err.println("Exception while closing scanner " + e.toString());
}
}
return null;
}
public static String searchUsingBufferedReader(String filePath, String searchQuery) throws IOException
{
searchQuery = searchQuery.trim();
BufferedReader br = null;
try
{
br = new BufferedReader(new InputStreamReader(new FileInputStream(filePath)));
String line;
while ((line = br.readLine()) != null)
{
if (line.contains(searchQuery))
{
return line;
}
else
{
}
}
}
finally
{
try
{
if (br != null)
br.close();
}
catch (Exception e)
{
System.err.println("Exception while closing bufferedreader " + e.toString());
}
}
return null;
}
}

Answer 2

Puede crear un Scanner separado para leer el archivo línea por línea y hacer una coincidencia de esa manera ...

final Scanner scanner = new Scanner(file);
while (scanner.hasNextLine()) {
final String lineFromFile = scanner.nextLine();
if(lineFromFile.contains(name)) {
// a match!
System.out.println("I found " +name+ " in file " +file.getName());
break;
}
}

Con respecto a si debe usar un Scanner o un BufferedReader para leer el archivo, lea esta respuesta .