Java StringWriter Tutorial with Examples

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StringWriter
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1- StringWriter

StringWriter is a subclass of Writer that manages a StringBuffer object. The characters written to the StringWriter will be appended to the StringBuffer object it manages.

Java String, StringBuffer and StringBuilder

The StringWriter class does not use I/O or Network operations so you can use it without closing it.

StringWriter constructor


StringWriter()    

StringWriter(int initialSize)

Besides those methods inherited from its parent class, StringWriter also has a few more notable methods of its own, including:

String toString()	Returns the String of the buffer.
StringBuffer getBuffer()	Returns the StringBuffer object that StringWriter is currently managing.
StringWriter append( char c)	Append a character to the buffer, the same as calling StringWriter.write(char) method, but this method returns the current StringWriter object, this allows calling another method of StringWriter instead of terminating with a semicolon (;)
StringWriter append( CharSequence csq)	Similar to the StringWriter.write(CharSequence) method, but returns the current StringWriter object.
StringWriter append( CharSequence csq, int start, int end)	Similar to the StringWriter.write(CharSequence,int,int) method, but returns the current StringWriter object.

2- Examples

StringWriterEx1.java


package org.o7planning.stringwriter.ex;

import java.io.StringWriter;

public class StringWriterEx1 {

    public static void main(String[] args) {
        StringWriter sw = new StringWriter();
        
        sw.write("Java Tutorial");
        sw.append("\n").append("C# Tutorial").append("\n").append("Python Tutorial");
        
        String s = sw.toString();
        
        System.out.println(s);
    }
}

Output:


Java Tutorial
C# Tutorial
Python Tutorial

Usually when an exception occurs, you often see "Stack Trace" information printed on the Console screen, how to get this content as a String?

StringWriterEx3.java


package org.o7planning.stringwriter.ex;

import java.io.PrintWriter;
import java.io.StringWriter;

public class StringWriterEx3 {

    public static void main(String[] args) {
        try {
            int a = 100/0; // Exception occur here
        } catch(Exception e)  {
            String s = getStackTrace(e);
            System.err.println(s);
        }
    }
    
    public static String getStackTrace(Throwable t)  {
        StringWriter writer = new StringWriter();
        
        // Create PrintWriter via PrintWriter(Writer) constructor.
        PrintWriter pw = new PrintWriter(writer);
        
        // Call method: Throwable.printStackTrace(PrintWriter)
        t.printStackTrace(pw);
        pw.close();
        
        String s = writer.getBuffer().toString();
        return s;
    }
}

Output:


java.lang.ArithmeticException: / by zero
    at org.o7planning.stringwriter.ex.StringWriterEx5.main(StringWriterEx5.java:10)

Java PrintWriter

GetStackTraceEx.java


package org.o7planning.printwriter.ex;

import java.io.PrintWriter;
import java.io.StringWriter;

public class GetStackTraceEx {

    public static void main(String[] args) {
        try {
            int a = 100/0; // Exception occur here
        } catch(Exception e)  {
            String s = getStackTrace(e);
            System.err.println(s);
        }
    }
     
    public static String getStackTrace(Throwable t)  {
        StringWriter stringWriter = new StringWriter();
         
        // Create PrintWriter via PrintWriter(Writer) constructor.
        PrintWriter pw = new PrintWriter(stringWriter);
         
        // Call method: Throwable.printStackTrace(PrintWriter)
        t.printStackTrace(pw);
        pw.close();
         
        String s = stringWriter.getBuffer().toString();
        return s;
    }
}

Output:


java.lang.ArithmeticException: / by zero
    at org.o7planning.printwriter.ex.GetStackTraceEx.main(GetStackTraceEx.java:10)

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