Reading properties from a file with example

Reading properties from file, find list of files in a directory and find a year is leap year or not. These all example present in this post.

Read properties from file:
          Reading properties from properties(.properties) file is the major requirement in real-time applications. Here, we will come to know, how to read properties from file with an example explanation.

          We will create one .properties file with the name of javaex.properties under src package and we will declare roleId's as key-value pairs. Like below,

application.id.roleIds = '53','121','63','46','43','71','45','36','64'

          Here, application.id.roleIds is the Key to get the values, which  we will use in java class. The below program explains you how to read data from the properties file by using the key which you have declared in properties file.

package com.javatbrains.practice;

import java.io.FileNotFoundException;
import java.io.InputStream;
import java.util.Properties;

public class CommaSeparated {
     public static void main(String[] args) throws Exception {
          try {
              InputStream stream = CommaSeparated.class.getClassLoader()
                        .getResourceAsStream("javaex.properties");
              Properties prop = new Properties();
              prop.load(stream);
              String roleIds = prop.getProperty("application.id.roleIds");
              String[] roleId = roleIds.split(",");
              for (int i = 0; i <= roleId.length - 1; i++) {
                   System.out.println("Role id is = " + roleId[i]);
              }
          } catch (FileNotFoundException e) {
              e.printStackTrace();
          }
     }
}
OutPut:
     Role id is = '53'
     Role id is = '121'
     Role id is = '63'
     Role id is = '46'
     Role id is = '43'
     Role id is = '71'
     Role id is = '45'
     Role id is = '36'
     Role id is = '64'

Steps:
            •  getClassLoader().getResourceAsStream() method to loads the entire .properties file and stores into  InputStream
           •  Create an object for Properties class, and loads input stream instance into Properties class by using load method.
           •  By passing the .properties file key into getProperty method we will get matching value of passing key and assigned to String.
           • Deviding the String value where all comma(,) is matching, and processing the results by using the for loop.

List of files in a directory:
          Here is the one more real-time scenario, like how to get list of file names in passing input directory. The below example will explains you to how to get list of files and sub-directories name in you C:\ drive. If you want to get some other directory files list, you can change passing input directory to your directory. Also it will print total no.of files in the console.

package com.javatbrains.practice;

import java.io.File;

public class ListOfFiles {
     public static void main(String[] args) {
          File f = null;
          String[] paths;
          try {
              f = new File("C:/");
              paths = f.list();
              for (String path : paths) {
                   System.out.println(f + "\\" + path);
              }
              System.out.println("Total no.of files : " + paths.length);
          } catch (Exception e) {
              e.printStackTrace();
          }
     }
}

Steps:
            •  First we need to create File object and passing input directory into File("C:/") constructor only.
            • list() method is used for getting list of files in your passing input directory, and store into String[] array.
            •  Finally process the results by using the for loop and show all the files path on console.

Find passing year is a leap year or not:
          Finding an year is a leap year or not is not a big challenge of the programmer in java. It is two steps process to find an year is leap or not. Let us write a program to test whether a given year is leap or not. The following logic used for doing so:

            • If year is representing the beginning of a new century like 1900,2000 etc. It should be divisible by 400. Then it is called leap year. To know whether the given year is leap century year or not, we should divide it by 100. If it is divisible by 100, then it is a century year.
           •  If the year is not century year like 1998,2007,2010, etc. It should be divisible by 4. Then it becomes leap year.
           • If any of the above two cases are satisfied, then that year is called leap year, otherwise it is not a leap year.
          Here, is the program to find passing year is leap or not.

package com.javatbrains.practice;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Leap {
     public static void main(String[] args) throws NumberFormatException,
              IOException {

          // accept year
          BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
          System.out.print("Enter year no: ");
          int year = Integer.parseInt(br.readLine());

          // If it is century year and divisible by 400
          if (year % 100 == 0 || year % 400 == 0) {
              System.out.println("It is leap year");

              // if it is not a century year and divisible by 4
          } else if (year % 4 == 0 || year % 100 == 0) {
              System.out.println("It is leap");
          } else {
              System.out.println("It is not leap");
          }
     }
}

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