How to make sure that I am calling a certain method only whenever there is any change in the database?

Question

What's the best way to accomplish this problem? I want to call a particular method for the first time when I am running my application but second time it should be called only whenever there is any change. If there is no change then I don't want to call that method.

I want to call process method for the first time when I am running my application and it should print out like this- I don't want to use TestingFramework entry in process method call.

{Answer-A=1.0.0, Answer-B=1.0.0}

But after that I have a background thread running which will call getAttributesFromDatabase method again so now I want to print out only the information that got changed but if there is no change then I don't want to call process method again.

Suppose any value got changed for either Animal-A or Animal-B, then it should print out only the change information only..

Let's take an example- Suppose second time when my background thread is running, and map entry is like this without any change-

TestingFramework 1.0.0
Answer-A         1.0.0
Asnwer-B         1.0.0

then I don't want to call process method again as there was no change. But somehow supposed the value entry got changed for Answer-A or Answer-B, then at that time, I want to call process method with the entry that got changed.

I hope the question is clear enough.

public static Map<String, String> frameworkInfo = new LinkedHashMap<String, String>();
public static Map<String, String> bundleList = new LinkedHashMap<String, String>();
public static Map<String, String> newBundleList = new LinkedHashMap<String, String>();
private static Map<String, String> oldBundleList = new LinkedHashMap<String, String>();

public static void main(String[] args) {

    getAttributesFromDatabase();

    loggingAfterEveryXMilliseconds();

}

private static void getAttributesFromDatabase() {

    Map<String, String> bundleInformation = new LinkedHashMap<String, String>();

    bundleInformation = getFromDatabase();

    if(TestingFrameworkInfo.get("TestingFramework") != (bundleInformation.get("TestingFramework"))) {
        TestingFrameworkInfo.put("TestingFramework", bundleInformation.get("TestingFramework"));    
        String version = TestingFrameworkInfo.get("TestingFramework");
        printTestingFrameworkBundle("TestingFramework", version);
    }

    bundleInformation.remove("TestingFramework");

    if(!bundleInformation.isEmpty()) {
        oldBundleList = bundleList;
        bundleList = bundleInformation;
    }

    final Map<String, MapDifference.ValueDifference<String>> entriesDiffering = Maps.difference(oldBundleList, bundleList).entriesDiffering();
    if (!entriesDiffering.isEmpty()) {
        for (String key : entriesDiffering.keySet()) {
            newBundleList.put(key, bundleList.get(key));
            System.out.println("{" + key + "=" + bundleList.get(key) + "}");
        } 

        process(newBundleList);
    }
    process(bundleList);
}


private static void process(final Map<String, String> test) {
    System.out.println(test);
}


private static Map<String, String> getFromDatabase() {

    Map<String, String> hello = new LinkedHashMap<String, String>();

    String version0 = "1.0.0";
    String version1 = "1.0.0";
    String version2 = "1.0.0";

    hello.put("TestingFramework", version0);
    hello.put("Answer-A", version1);
    hello.put("Answer-B", version2);

    return hello;
}

private static void loggingAfterEveryXMilliseconds() {
    new Thread() {
        public void run() {
            while (true) {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException ex) {

                }
                getAttributesFromDatabase();

            }
        }
    }.start();
}

With the below code, I have, it will call the process method for the first time and second time when there is no change then again it calls the process method which I don't want at all. Can anybody help me with this?

I am pretty much sure, I am missing one key thing here, and then it will start working I guess.

Updated:-

I am still working on this. Can anybody help me with this?

Answer 1

If your database is an RDBMS, you could put the logic to detect a change there, i.e. use a trigger to update a last modified column that your application would poll and call your process method when it changes.