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?

• 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(.

Answer 1

import org.apache.commons.io.IOUtils;
String string = IOUtils.toString(reader);

• viking: See @Kiran's answer for a Java 9+ solution that does not use external libraries.

Answer 2

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);

• viking: See @Kiran's answer for a Java 9+ solution that is much simpler.

Answer 3

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.

Answer 4

Or using CharStreams from Googles Guava library:

CharStreams.toString(stringReader);

• viking: See @Kiran's answer for a Java 9+ solution that does not use external libraries.

Answer 5

As per https://www.tutorialspoint.com/java/io/stringwriter_tostring.htm

StringReader sr = new StringReader("hello");
StringWriter sw = new StringWriter();
sr.transferTo(sw);
System.out.println(sw.toString());

• viking: This is the right answer for Java 10+. Note that Reader gained this method in Java 10 and InputStream gained this method in Java 9. Under the hood, this takes advantage of a character buffer of size 8192 bytes in both cases and uses StringBuffer.append in the StringWriter. This version will not have issues with removing line endings.

Answer 6

reader.toString(); will give you the results of calling the generic toString() method from Object class.

You can use the read() method:

int i; 
do {
 i = reader.read();
 char c = (char) i;
 // do whatever you want with the char here...
} while (i != -1); 

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

Answer 7

Calling toString() method will give the object of StringReader class. If yo want it's content then you need to call the read method on StringReader like this:

public class StringReaderExample {
 public static void main(String[] args) {
 String s = "Hello World";
 // create a new StringReader
 StringReader sr = new StringReader(s);
 try {
 // read the first five chars
 for (int i = 0; i < 5; i++) {
 char c = (char) sr.read();
 System.out.print("" + c);
 }
 // close the stream
 sr.close();
 } catch (IOException ex) {
 ex.printStackTrace();
 }
 }
}

For tutorials you can use this link.

Answer 8

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);
}

Answer 9

You're printing out the toString() of the actual StringReader object, NOT the contents of the String that the StringReader is reading.

You need to use the read() and/or the read(char[] cbuf, int off, int len) methods to read the actual chars in the String.

Answer 10

If you use the method toString() in a StringReader object you will print the memory position of the object. You have yo use one of this method:

read() Reads a single character.

read(char[] cbuf, int off, int len) Reads characters into a portion of an array.

Here an example:

 String s = "Hello World";
 // create a new StringReader
 StringReader sr = new StringReader(s);
 try {
 // read the first five chars
 for (int i = 0; i < s.length(); i++) {
 char c = (char) sr.read();
 System.out.print("" + c);
 }
 // close the stream
 sr.close();
 } catch (IOException ex) {
 ex.printStackTrace();
 }