How do I convert a StringReader to a String?

Question

I'm trying to convert my StringReader back to a regular String, as shown:

String string = reader.toString();

But when I try to read this string out, like this:

System.out.println("string: "+string);

All I get is a pointer value, like this:

java.io.StringReader@2c552c55

Am I doing something wrong in reading the string back?

Solution 1

The StringReader's toString method does not return the StringReader internal buffers.

You'll need to read from the StringReader to get this.

I recommend using the overload of read which accepts a character array. Bulk reads are faster than single character reads.

ie.

//use string builder to avoid unnecessary string creation.
StringBuilder builder = new StringBuilder();
int charsRead = -1;
char[] chars = new char[100];
do{
    charsRead = reader.read(chars,0,chars.length);
    //if we have valid chars, append them to end of string.
    if(charsRead>0)
        builder.append(chars,0,charsRead);
}while(charsRead>0);
String stringReadFromReader = builder.toString();
System.out.println("String read = "+stringReadFromReader);

Solution 2

import org.apache.commons.io.IOUtils;

String string = IOUtils.toString(reader);

Solution 3

Or using CharStreams from Googles Guava library:

CharStreams.toString(stringReader);

Solution 4

If you prefer not to use external libraries:

 Scanner scanner = new Scanner(reader).useDelimiter("\\A");
 String str = scanner.hasNext() ? scanner.next() : "";

The reason for the hasNext() check is that next() explodes with a NoSuchElementException if the reader wraps a blank (zero-length) string.

Solution 5

Another native (Java 8+) solution could be to pass the StringReader object to a BufferedReader and stream trough the lines:

try (BufferedReader br = new BufferedReader(stringReader)) {
  br.lines().forEach(System.out::println);
}

View more solutions

Comments

[Matt Ball]

Clearly, you are. docs.oracle.com/javase/7/docs/api/java/io/StringReader.html

[nanofarad]

You can't get the string back from a stringreader without using read(.

[William Morrison]

A bulk read with an array will be faster than reading a single character at a time.