CODEWITHSUNDEEP
javafileunicodeencoding
nybon
nybon

Reputation: 9631

Java FileReader encoding issue

I tried to use java.io.FileReader to read some text files and convert them into a string, but I found the result is wrongly encoded and not readable at all.

Here's my environment:

My files are UTF-8 encoded or CP1252 encoded, and some of them (UTF-8 encoded files) may contain Chinese (non-Latin) characters.

I use the following code to do my work:

   private static String readFileAsString(String filePath)
    throws java.io.IOException{
        StringBuffer fileData = new StringBuffer(1000);
        FileReader reader = new FileReader(filePath);
        //System.out.println(reader.getEncoding());
        BufferedReader reader = new BufferedReader(reader);
        char[] buf = new char[1024];
        int numRead=0;
        while((numRead=reader.read(buf)) != -1){
            String readData = String.valueOf(buf, 0, numRead);
            fileData.append(readData);
            buf = new char[1024];
        }
        reader.close();
        return fileData.toString();
    }

The above code doesn't work. I found the FileReader's encoding is CP1252 even if the text is UTF-8 encoded. But the JavaDoc of java.io.FileReader says that:

The constructors of this class assume that the default character encoding and the default byte-buffer size are appropriate.

Does this mean that I am not required to set character encoding by myself if I am using FileReader? But I did get wrongly encoded data currently, what's the correct way to deal with my situtaion? Thanks.

Upvotes: 138

Views: 215174

Answers (6)

Joachim Sauer
Joachim Sauer

Reputation: 308159

Yes, you need to specify the encoding of the file you want to read.

Yes, this means that you have to know the encoding of the file you want to read.

No, there is no general way to guess the encoding of any given "plain text" file.

The one-arguments constructors of FileReader always use the platform default encoding which is generally a bad idea.

Since Java 11 FileReader has also gained constructors that accept an encoding: new FileReader(file, charset) and new FileReader(fileName, charset).

In earlier versions of java, you need to use new InputStreamReader(new FileInputStream(pathToFile), <encoding>).

Upvotes: 272

Iefimenko Ievgen
Iefimenko Ievgen

Reputation: 401

For another as Latin languages for example Cyrillic you can use something like this:

FileReader fr = new FileReader("src/text.txt", StandardCharsets.UTF_8);

and be sure that your .txt file is saved with UTF-8 (but not as default ANSI) format. Cheers!

Upvotes: 0

Guangtong Shen
Guangtong Shen

Reputation: 1422

FileInputStream with InputStreamReader is better than directly using FileReader, because the latter doesn't allow you to specify encoding charset.

Here is an example using BufferedReader, FileInputStream and InputStreamReader together, so that you could read lines from a file. 

List<String> words = new ArrayList<>();
List<String> meanings = new ArrayList<>();
public void readAll( ) throws IOException{
    String fileName = "College_Grade4.txt";
    String charset = "UTF-8";
    BufferedReader reader = new BufferedReader(
        new InputStreamReader(
            new FileInputStream(fileName), charset)); 

    String line; 
    while ((line = reader.readLine()) != null) { 
        line = line.trim();
        if( line.length() == 0 ) continue;
        int idx = line.indexOf("\t");
        words.add( line.substring(0, idx ));
        meanings.add( line.substring(idx+1));
    } 
    reader.close();
}

Upvotes: 1

Andreas Gelever
Andreas Gelever

Reputation: 2026

For Java 7+ doc you can use this:

BufferedReader reader = Files.newBufferedReader(path, StandardCharsets.UTF_8);

Here are all Charsets doc

For example if your file is in CP1252, use this method

Charset.forName("windows-1252");

Here is other canonical names for Java encodings both for IO and NIO doc

If you do not know with exactly encoding you have got in a file, you may use some third-party libs like this tool from Google this which works fairly neat.

Upvotes: 15

Radoslav Ivanov
Radoslav Ivanov

Reputation: 1072

Since Java 11 you may use that:

public FileReader(String fileName, Charset charset) throws IOException;

Upvotes: 8

Michael Borgwardt
Michael Borgwardt

Reputation: 346457

FileReader uses Java's platform default encoding, which depends on the system settings of the computer it's running on and is generally the most popular encoding among users in that locale.

If this "best guess" is not correct then you have to specify the encoding explicitly. Unfortunately, FileReader does not allow this (major oversight in the API). Instead, you have to use new InputStreamReader(new FileInputStream(filePath), encoding) and ideally get the encoding from metadata about the file.

Upvotes: 80

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