For easy understanding of RMI concept, RMI Tutorial is given in Questions and Answers format. Remote method invocation(RMI) allow a java object to invoke method on an object running on another machine. RMI provide remote communication between java program. RMI is used for building distributed application.

Concept of RMI application

Stub and Skeleton

Creating a Simple RMI application involves following steps

1. What is Java RMI?

2. What is remote method?

3. Then what is invocation?

4. Give a practical example, to be more clear in this RMI tutorial?

5. What is distributed communication? Explain for beginners

6. What a distributed application should satisfy?

7. As it given an example of bank transaction, does RMI take care of transaction management also?

8. What protocol RMI uses?

9. What is object communication?

10. What is remote object?

11. What are the features of RMI?

12. What is distributed garbage collection?

13. What is the architecture of RMI?

14. How many layers exists in RMI Architecture?

15. What an RMI application comprises of?

16. What is the process of compilation, execution and distribution (on client and server) of the programs involved in RMI application?

How to create a File in Java

In this tutorial we will see how to create a file in Java using createNewFile() method. This method creates an empty file, if the file doesn’t exist at the specified location and returns true. If the file is already present then this method returns false. It throws:

IOException – If an Input/Output error occurs during file creation.
SecurityException – If a security manager exists and its SecurityManager.checkWrite(java.lang.String) method denies write access to the file.

Complete code:
The below code would create a txt file named “newfile.txt” in C drive. You can change the path in the below code in order to create the file in different directory or in different drive.

package beginnersbook.com;

import java.io.File;

import java.io.IOException;

public class CreateFileDemo

{

   public static void main( String[] args )

   {       

      try {

                 File file = new File("C:\\newfile.txt");

                 /*If file gets created then the createNewFile() 

                  * method would return true or if the file is 

                  * already present it would return false

                  */

             boolean fvar = file.createNewFile();

                 if (fvar){

                      System.out.println("File has been created successfully");

                 }

                 else{

                      System.out.println("File already present at the specified location");

                 }

            } catch (IOException e) {

                        System.out.println("Exception Occurred:");

                    e.printStackTrace();

              }

   }

}

How to read file in Java – BufferedInputStream

In this example we will see how to read a file in Java using FileInputStream and BufferedInputStream. Here are the detailed steps that we have taken in the below code:
1) Created a File instance by providing the full path of the file(which we will read) during File Object creation.
2) Passed the file instance to the FileInputStream which opens a connection to the actual file, the file named by the File object file in the file system.
3) Passed the FileInputStream instance to BufferedInputStream which creates a BufferedInputStream and saves its argument, the input stream in, for later use. An internal buffer array is created and stored in buf using which the read operation gives good performance as the content is readily available in the buffer.
4) Used while loop to read the file. Method available() is used for checking the end of the file as it returns 0 when the pointer reaches to the end of the file. Read the file content using read() method of FileInputStream.

package beginnersbook.com;

import java.io.*;

public class ReadFileDemo {

   public static void main(String[] args) {         

      //Specify the path of the file here

      File file = new File("C://myfile.txt");

      BufferedInputStream bis = null;

      FileInputStream  fis= null;

      try

      {

          //FileInputStream to read the file

          fis = new FileInputStream(file);

          /*Passed the FileInputStream to BufferedInputStream

           *For Fast read using the buffer array.*/

          bis = new BufferedInputStream(fis);

          /*available() method of BufferedInputStream

           * returns 0 when there are no more bytes

           * present in the file to be read*/

          while( bis.available() > 0 ){                    

              System.out.print((char)bis.read());

          }

       }catch(FileNotFoundException fnfe)

        {

            System.out.println("The specified file not found" + fnfe);

        }

        catch(IOException ioe)

        {

            System.out.println("I/O Exception: " + ioe); 

        }

        finally

        {

            try{

               if(bis != null && fis!=null)

               {

                      fis.close();

                  bis.close();

               }      

             }catch(IOException ioe)

              {

                  System.out.println("Error in InputStream close(): " + ioe);

              }         

        }

   }    

}

How to read file in Java using BufferedReader

In this tutorial we will see two ways to read a file using BufferedReader.

Method 1: Using readLine() method of BufferedReader class.

public String readLine() throws IOException

It reads a line of text.

Method 2: Using read() method

public int read() throws IOException

It reads a character of text. Since it returns an integer value, it needs to be explicitly cast as char for reading the content of file.

Complete example

Here I have two txt files myfile.txt and myfile2.txt. In order to demonstrate both the ways to read file. I’m reading first file using readLine() method while the second file is being read using read()method.

package beginnersbook.com;

import java.io.BufferedReader;

import java.io.FileReader;

import java.io.IOException;

public class ReadFileDemo {

   public static void main(String[] args) {

       BufferedReader br = null;

       BufferedReader br2 = null;

       try{           

           br = new BufferedReader(new FileReader("B:\\myfile.txt"));                  

           //One way of reading the file

               System.out.println("Reading the file using readLine() method:");

               String contentLine = br.readLine();

               while (contentLine != null) {

                  System.out.println(contentLine);

                  contentLine = br.readLine();

               }

               br2 = new BufferedReader(new FileReader("B:\\myfile2.txt"));

               //Second way of reading the file

               System.out.println("Reading the file using read() method:");

               int num=0;

               char ch;

               while((num=br2.read()) != -1)

               {       

               ch=(char)num;

                   System.out.print(ch);

               }

       } 

       catch (IOException ioe) 

       {

               ioe.printStackTrace();

       } 

       finally 

       {

               try {

                  if (br != null)

                         br.close();

                  if (br2 != null)

                         br2.close();

               } 

               catch (IOException ioe) 

           {

                        System.out.println("Error in closing the BufferedReader");

               }

            }

   }

}

How to write to a file in java using FileOutputStream

Earlier we saw how to create a file in Java. In this tutorial we will see how to write to a file in java using FileOutputStream. We would be using write() method of FileOutputStream to write the content to the specified file. Here is the signature of write() method.

public void write(byte[] b) throws IOException

It writes b.length bytes from the specified byte array to this file output stream. As you can see this method needs array of bytes in order to write them into a file. Hence we would need to convert our content into array of bytes before writing it into the file.

Complete Code: Writing to a File

In the below example we are writing a String to a file. To convert the String into an array of bytes, we are using getBytes() method of String class.

import java.io.File;

import java.io.FileOutputStream;

import java.io.IOException;

public class WriteFileDemo {

   public static void main(String[] args) {

      FileOutputStream fos = null;

      File file;

      String mycontent = "This is my Data which needs" +

                 " to be written into the file";

      try {

          //Specify the file path here

              file = new File("C:/myfile.txt");

              fos = new FileOutputStream(file);

          /* This logic will check whether the file

               * exists or not. If the file is not found

               * at the specified location it would create

               * a new file*/

              if (!file.exists()) {

                 file.createNewFile();

              }

              /*String content cannot be directly written into

               * a file. It needs to be converted into bytes

               */

              byte[] bytesArray = mycontent.getBytes();

              fos.write(bytesArray);

              fos.flush();

              System.out.println("File Written Successfully");

       } 

       catch (IOException ioe) {

              ioe.printStackTrace();

       } 

       finally {

              try {

                 if (fos != null) 

                 {

                         fos.close();

                 }

          } 

              catch (IOException ioe) {

                 System.out.println("Error in closing the Stream");

              }

       }

   }

}

Output:

File Written Successfully

How to write to file in Java using BufferedWriter

Earlier we discussed how to write to a file using FileOutputStream. In this tutorial we will see how to write to a file using BufferedWriter. We will be using write() method of BufferedWriter to write the text into a file. The advantage of using BufferedWriter is that it writes text to a character-output stream, buffering characters so as to provide for the efficient writing (better performance) of single characters, arrays, and strings.

Complete example: Write to file using BufferedWriter

In this example we have a String mycontent and a file myfile.txt in C drive. We are writing the String to the File with the help of FileWriter and BufferedWriter.

package beginnersbook.com;

import java.io.BufferedWriter;

import java.io.File;

import java.io.FileWriter;

import java.io.IOException;

public class WriteFileDemo {

   public static void main(String[] args) {

      BufferedWriter bw = null;

      try {

             String mycontent = "This String would be written" +

                " to the specified File";

         //Specify the file name and path here

             File file = new File("C:/myfile.txt");

             /* This logic will make sure that the file 

              * gets created if it is not present at the

              * specified location*/

              if (!file.exists()) {

                 file.createNewFile();

              }

              FileWriter fw = new FileWriter(file);

              bw = new BufferedWriter(fw);

              bw.write(mycontent);

          System.out.println("File written Successfully");

      } catch (IOException ioe) {

               ioe.printStackTrace();

            }

            finally

            { 

               try{

                  if(bw!=null)

                         bw.close();

               }catch(Exception ex){

                   System.out.println("Error in closing the BufferedWriter"+ex);

                }

            }

   }

}

Output:

File written Successfully

Append to a file in java using BufferedWriter, PrintWriter, FileWriter

In this tutorial we will learn how to append content to a file in Java. There are two ways to append:

1) Using FileWriter and BufferedWriter: In this approach we will be having the content in one of more Strings and we will be appending those Strings to the file. The file can be appended using FileWriteralone however using BufferedWriter improves the performance as it maintains a buffer.
2) Using PrintWriter: This is one of best way to append content to a file. Whatever you write using PrintWriter object would be appended to the File.

1) Append content to File using FileWriter and BufferedWriter

import java.io.File;

import java.io.FileWriter;

import java.io.BufferedWriter;

import java.io.IOException;

class AppendFileDemo

{

   public static void main( String[] args )

   {       

      try{

            String content = "This is my content which would be appended " +

            "at the end of the specified file";

        //Specify the file name and path here

            File file =new File("C://myfile.txt");

            /* This logic is to create the file if the

             * file is not already present

             */

            if(!file.exists()){

               file.createNewFile();

            }

            //Here true is to append the content to file

            FileWriter fw = new FileWriter(file,true);

            //BufferedWriter writer give better performance

            BufferedWriter bw = new BufferedWriter(fw);

            bw.write(content);

            //Closing BufferedWriter Stream

            bw.close();

            System.out.println("Data successfully appended at the end of file");

      }catch(IOException ioe){

         System.out.println("Exception occurred:");

             ioe.printStackTrace();

       }

   }

}

Output:

Data successfully appended at the end of file

Lets say myfile.txt content was:

This is the already present content of my file

After running the above program the content would be:

This is the already present content of my fileThis is my content which 

would be appended at the end of the specified file

2) Append content to File using PrintWriter

PrintWriter gives you more flexibility. Using this you can easily format the content which is to be appended to the File.

import java.io.File;

import java.io.FileWriter;

import java.io.PrintWriter;

import java.io.BufferedWriter;

import java.io.IOException;

class AppendFileDemo2

{

   public static void main( String[] args )

   {       

      try{

          File file =new File("C://myfile.txt");

              if(!file.exists()){

                        file.createNewFile();

              }

              FileWriter fw = new FileWriter(file,true);

              BufferedWriter bw = new BufferedWriter(fw);

              PrintWriter pw = new PrintWriter(bw);

          //This will add a new line to the file content

              pw.println("");

          /* Below three statements would add three 

           * mentioned Strings to the file in new lines.

           */

              pw.println("This is first line");

              pw.println("This is the second line");

              pw.println("This is third line");

              pw.close();

              System.out.println("Data successfully appended at the end of file");

       }catch(IOException ioe){

               System.out.println("Exception occurred:");

               ioe.printStackTrace();

      }

   }

}

Output:

Data successfully appended at the end of file

Lets say myfile.txt content was:

This is the already present content of my file

After running the above program the content would be:

This is the already present content of my file

This is first line

This is the second line

This is third line

Delete/Rename File

File compression

Misc