Java Cookbook

Reading a File into a String

Problem

You need to read the entire contents of a file into a string.

Solution

Use my FileIO.readerToString( ) method.

Discussion

This is not a common activity in Java, but there will be times when you really want to do it. For example, you might want to load a file into a “text area” in a GUI. Or process an entire file looking for multiline regular expressions (as in Section 4.13). Even though there’s nothing in the standard API to do this, it’s still easy to accomplish with the readerToString( ) method in com.darwinsys.util.FileIO. You just say something like the following:

Reader is = new FileReader(theFileName);
String input = FileIO.readerToString(is);

The readerToString( ) method is fairly simple, based on what you’ve already seen:

// Part of com.darwinsys.util/FileIO.java
 
/** Read the entire content of an Reader into a String */
public static String readerToString(Reader is) throws IOException {
        StringBuffer sb = new StringBuffer(  );
        char[] b = new char[BLKSIZ];
        int n;
 
        // Read a block. If it gets any chars, append them.
        while ((n = is.read(b)) > 0) {
                sb.append(b, 0, n);
        }
 
        // Only construct the String object once, here.
        return sb.toString(  );
}
 
/** Read the content of a Stream into a String */
public static String inputStreamToString(InputStream is)
throws IOException {
        return readerToString(new InputStreamReader(is));
}