The HashMap class in Java implements the Serializable interface so that its objects can be written or serialized to a file using the ObjectOutputStream. However, the output file it produces is not in the human-readable format and may contain junk characters.
Serialization: It is a process of writing an Object into a file along with its attributes and content. It internally converts the object into a stream of bytes.
De-Serialization: It is a process of reading the Object and its properties from a file along with the Object’s content.
If we want to write a HashMap object to a plain text file, we need a simple and understandable code to write on the HashMap and then insert the Map into the Text File. We can write the code in the form of key-Value Pair of a map Object to a File and each line File will contain the Key-Value Pair
Approach
- In the below class we are storing the HashMap content in a hashmap.ser serialized file.
- Once when we run the below code it would produce a hashmap.ser file. This file would be used in the next class for de-serialization.
- The hashmap.ser serialised file can be Stored to any Location with describing it’s Location Like Below
- So we need the Location to write the HashMap in it.
- So for that need to Provide the External Location to Store the HashMapÂ
final static String outputFilePath = "F:/Serialisation/write.txt";
Create the HashMap of String Key and String Value Pair
HashMap<String, String> map = new HashMap<String, String>();
Create the File Object:
File file = new File(outputFilePath);
Using the file object we will write the HashMap input using the function BufferedWriter(File_Path)
bf = new BufferedWriter( new FileWriter(file));
and then at last close the FileÂ
bf.close();
Writing to FileÂ
Java
// Java program to write HashMap to a file  import java.io.*;import java.util.*;  class GFG {      final static String outputFilePath        = "F:/Serialisation/write.txt";      public static void main(String[] args)    {          // create new HashMap        HashMap<String, String> map            = new HashMap<String, String>();          // key-value pairs        map.put("rohit", "one");        map.put("Sam", "two");        map.put("jainie", "three");          // new file object        File file = new File(outputFilePath);          BufferedWriter bf = null;          try {              // create new BufferedWriter for the output file            bf = new BufferedWriter(new FileWriter(file));              // iterate map entries            for (Map.Entry<String, String> entry :                 map.entrySet()) {                  // put key and value separated by a colon                bf.write(entry.getKey() + ":"                         + entry.getValue());                  // new line                bf.newLine();            }              bf.flush();        }        catch (IOException e) {            e.printStackTrace();        }        finally {              try {                  // always close the writer                bf.close();            }            catch (Exception e) {            }        }    }} |
Output:
