Storing state in Java

Question

Broad discussion question. Are there any libraries already which allow me to store the state of execution of my application in Java?

E.g I have an application which processes files, now the application may be forced to shutdown suddenly at some point.I want to store the information on what all files have been processed and what all have not been, and what stage the processing was on for the ongoing processes.

Are there already any libraries which abstract this functionality or I would have to implement it from scratch?

Answer 1

It seems like what you are looking for is serialization which can be performed with the Java Serialization API.

You can write even less code if you decide to use known libraries such as Apache Commons Lang, and its SerializationUtils class which itself is built on top the Java Serialization API.

Using the latest, serializing/deserializing your application state into a file is done in a few lines.

The only thing you have to do is create a class holding your application state, let's call it... ApplicationState :-) It can look like that:

class ApplicationState {

 enum ProcessState {
  READ_DONE,
  PROCESSING_STARTED,
  PROCESSING_ENDED,
  ANOTHER_STATE;
 }

 private List<String> filesDone, filesToDo;
 private String currentlyProcessingFile;
 private ProcessState currentProcessState;
}

With such a structure, and using SerializationUtils, serializing is done the following way:

try {
      ApplicationState state = new ApplicationState();
      ...
      // File to serialize object to
      String fileName = "applicationState.ser";

      // New file output stream for the file
      FileOutputStream fos = new FileOutputStream(fileName);

      // Serialize String
      SerializationUtils.serialize(state, fos);
      fos.close();

      // Open FileInputStream to the file
      FileInputStream fis = new FileInputStream(fileName);

      // Deserialize and cast into String
      String ser = (String) SerializationUtils.deserialize(fis);
      System.out.println(ser);
      fis.close();
    } catch (Exception e) {
      e.printStackTrace();
    }