Guava: Files class

Files class provides number of utility methods to work with Files. By using Files class you can do following functions effectively.

Copying files

Files class provides copy method to copy contents of a file to another file.

Method	Description
public static void copy(File from, OutputStream to) throws IOException	Copy contents of a file to output stream.
public static void copy(File src, File destination) throws IOException	Copy contents of src file to destination file. If destination file already exists, then contents of destination file are overwritten.
public static void copy(File from, Charset charset, Appendable to)	Copies contents of a file to an appendable object,using the given character set.

Copy source file to destination

import java.io.File;
import java.io.IOException;

import com.google.common.io.Files;

public class FilesEx {
  public static void main(String args[]) throws IOException {
    String src = "/Users/harikrishna_gurram/emp.txt";
    String destination = "/Users/harikrishna_gurram/emp_new.txt";

    System.out.println("Copying file from " + src + " to destination "
        + destination);
    Files.copy(new File(src), new File(destination));
    System.out.println("File copying done");
  }
}

Copy file data to console

import java.io.File;
import java.io.IOException;

import com.google.common.io.Files;

public class FilesEx {
  public static void main(String args[]) throws IOException {
    String src = "/Users/harikrishna_gurram/emp.txt";

    System.out.println(src + " contents are");
    Files.copy(new File(src), System.out);
  }
}

Move file from one location to another

Files class provides move method to move file from one location to another.

public static void move(File from, File to) throws IOException

import java.io.File;
import java.io.IOException;

import com.google.common.io.Files;

public class FilesEx {
  public static void main(String args[]) throws IOException {
    String src = "/Users/harikrishna_gurram/emp.txt";
    String destination = "/Users/harikrishna_gurram/emp_new.txt";

    Files.move(new File(src), new File(destination));

  }
}

Read file data as list of strings

Files class provides following methods to read file data as list of string. Each element in list represents a line of file.

Method	Description
public static String readFirstLine(File file, Charset charset)	Reads the first line from a file, charset used to decode the input stream.
public static List<String> readLines(File file, Charset charset)	Read all the lines from a file.
public static <T> T readLines(File file, Charset charset,LineProcessor<T> callback)	Streams lines from a File, stopping when our callback returns false, or we have read all of the lines. Returns the output of processing the lines

Read first line of file

import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;

import com.google.common.io.Files;

public class FilesEx {
  public static void main(String args[]) throws IOException {
    String src = "/Users/harikrishna_gurram/emp.txt";

    String firstLine = Files.readFirstLine(new File(src),
        Charset.defaultCharset());

    System.out.println(firstLine);

  }
}

Read all the lines from a file

import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;
import java.util.List;

import com.google.common.io.Files;

public class FilesEx {
  public static void main(String args[]) throws IOException {
    String src = "/Users/harikrishna_gurram/emp.txt";

    List<String> data = Files.readLines(new File(src),
        Charset.defaultCharset());

    for (String line : data) {
      System.out.println(line);
    }

  }
}

Read specific content from file as list of strings

Let’s say I had following csv file, which contains author name, title and price. I want to extract all the titles from csv file.

Harper Lee, To Kill a Mockingbird, 250

J.K. Rowling, Harry Potter and the Deathly Hallows, 450

Suzanne Collins, The Hunger Games, 325

Orson Scott Card, Ender's Game, 876

Jane Austen, Pride and Prejudice, 234

Markus Zusak, The Book Thief, 345

J.K. Rowling, Harry Potter and the Sorcerer's Stone, 546

First column contains author name, second column contains book title and third column contains price.

import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;
import java.util.List;

import com.google.common.base.Splitter;
import com.google.common.collect.Iterables;
import com.google.common.collect.Lists;
import com.google.common.io.Files;
import com.google.common.io.LineProcessor;

public class FilesEx {

  public static class TitlesExtractor implements LineProcessor<List<String>> {
    Splitter splitter = Splitter.on(",");
    List<String> authors = Lists.newArrayList();

    @Override
    public boolean processLine(String line) throws IOException {
      Iterable<String> columns = splitter.split(line);
      String author = Iterables.get(columns, 1);
      authors.add(author);
      return true;
    }

    @Override
    public List<String> getResult() {
      return authors;
    }

  }

  public static void main(String args[]) throws IOException {
    String src = "/Users/harikrishna_gurram/books.csv";

    List<String> titles = Files.readLines(new File(src),
        Charset.defaultCharset(), new TitlesExtractor());

    for (String line : titles) {
      System.out.println(line);
    }

  }
}

Output

To Kill a Mockingbird
 Harry Potter and the Deathly Hallows
 The Hunger Games
 Ender's Game
 Pride and Prejudice
 The Book Thief
 Harry Potter and the Sorcerer's Stone

Get Hash value for a file

You can compute the hash value for a file using hash function.

public static HashCode hash(File file, HashFunction hashFunction)

import java.io.File;
import java.io.IOException;

import com.google.common.hash.HashCode;
import com.google.common.hash.Hashing;
import com.google.common.io.Files;

public class FilesEx {

  public static void main(String args[]) throws IOException {
    String src = "/Users/harikrishna_gurram/books.csv";
    HashCode hashCode = Files.hash(new File(src), Hashing.sha256());

    System.out.println("Hash code for given file is ");
    System.out.println(hashCode);
  }
}

Writing data to files

Files class provides write method to write data to file.

public static void write(CharSequence from, File to, Charset charset)

Writes a character sequence to a file using the given character set.

import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;

import com.google.common.io.Files;

public class FilesEx {

  public static void main(String args[]) throws IOException {
    String to = "/Users/harikrishna_gurram/sample.txt";
    File file = new File(to);

    String data = "Hello, Welcome to Guava package\nHope you are enjoying tutorial";

    Files.write(data, file, Charset.defaultCharset());
  }
}

Append data to file

Files class provides append method to append data to a file.

public static void append(CharSequence from, File to, Charset charset)

Appends a character sequence to a file using the given character set.

import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;

import com.google.common.io.Files;

public class FilesEx {

  public static void main(String args[]) throws IOException {
    String to = "/Users/harikrishna_gurram/sample.txt";
    File file = new File(to);

    for (int i = 0; i < 20; i++) {
      Files.append("line " + i + "\n", file, Charset.defaultCharset());
    }
  }
}

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