What is simplest way to read a file into String? [duplicate]

Question

Yes, you can do this in one line (though for robust IOException handling you wouldn't want to).

String content = new Scanner(new File("filename")).useDelimiter("\\Z").next();
System.out.println(content);

This uses a java.util.Scanner, telling it to delimit the input with \Z, which is the end of the string anchor. This ultimately makes the input have one actual token, which is the entire file, so it can be read with one call to next().

There is a constructor that takes a File and a String charSetName (among many other overloads). These two constructor may throw FileNotFoundException, but like all Scanner methods, no IOException can be thrown beyond these constructors.

You can query the Scanner itself through the ioException() method if an IOException occurred or not. You may also want to explicitly close() the Scanner after you read the content, so perhaps storing the Scanner reference in a local variable is best.

See also

• Java Tutorials - I/O Essentials - Scanning and formatting

Related questions

• Validating input using java.util.Scanner - has many examples of more typical usage

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Third-party library options

For completeness, these are some really good options if you have these very reputable and highly useful third party libraries:

Guava

com.google.common.io.Files contains many useful methods. The pertinent ones here are:

• String toString(File, Charset)
  • Using the given character set, reads all characters from a file into a String
• List<String> readLines(File, Charset)
  • ... reads all of the lines from a file into a List<String>, one entry per line

Apache Commons/IO

org.apache.commons.io.IOUtils also offer similar functionality:

• String toString(InputStream, String encoding)
  • Using the specified character encoding, gets the contents of an InputStream as a String
• List readLines(InputStream, String encoding)
  • ... as a (raw) List of String, one entry per line

Related questions

• Most useful free third party Java libraries (deleted)?

From Java 7 (API Description) onwards you can do:

new String(Files.readAllBytes(Paths.get(filePath)), StandardCharsets.UTF_8);

Where filePath is a String representing the file you want to load.

You can use apache commons IO..

FileInputStream fisTargetFile = new FileInputStream(new File("test.txt"));

String targetFileStr = IOUtils.toString(fisTargetFile, "UTF-8");

This should work for you:

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;

public static void main(String[] args) throws IOException {
    String content = new String(Files.readAllBytes(Paths.get("abc.java")));
}

Using Apache Commons IO.

import org.apache.commons.io.FileUtils;

//...

String contents = FileUtils.readFileToString(new File("/path/to/the/file"), "UTF-8")

You can see de javadoc for the method for details.

Don't write your own util class to do this - I would recommend using Guava, which is full of all kinds of goodness. In this case you'd want either the Files class (if you're really just reading a file) or CharStreams for more general purpose reading. It has methods to read the data into a list of strings (readLines) or totally (toString).

It has similar useful methods for binary data too. And then there's the rest of the library...

I agree it's annoying that there's nothing similar in the standard libraries. Heck, just being able to supply a CharSet to a FileReader would make life a little simpler...

Another alternative approach is:

How do I create a Java string from the contents of a file?

Other option is to use utilities provided open source libraries
http://commons.apache.org/io/api-1.4/index.html?org/apache/commons/io/IOUtils.html

Why java doesn't provide such a common util API ?
a) to keep the APIs generic so that encoding, buffering etc is handled by the programmer.
b) make programmers do some work and write/share opensource util libraries :D ;-)