OAuthCore.java

public class OAuthCore {

  private AccessTokenInfo accessTokenInfo;
  private AtomicBoolean asyncRetrievalInProgress = new AtomicBoolean(false);
  private AtomicBoolean logout = new AtomicBoolean(false);

  private String getAccessToken(){
    return this.accessTokenInfo.accessToken;
  }

  public void reset() {
    // clear all tracking vars including logout.
  }

  // caller is expected to check if expired before calling this method, bcoz, this will take a
  // lock and wait for any other threads that are executing.
  public synchronized String retrieveAccessToken(){
    if(!accessTokenInfo.isExpired()){ // do we need to check for log out here.
      return accessTokenInfo.accessToken;
    } else if(!logout.get()){
      // fetch access token in blocking manner.
      // after fetching if log out -> set log out.
      // figure out how to convey the info to caller.
    } else{
      // already log out set. convey the info to caller.
    }
  }

  public void mayBeRetrieveTokenIfExpiringWithinDeltaTime(){
    if(asyncRetrievalInProgress.get()) {
      return;
    } else if(accessTokenInfo.isExpiringInDeltaTime(30000)) {
      // retrieve token async via thread and update value of accessTokenInfo.
    }
  }

  // within a thread.
  // can async call result in log out ? can we override the existing token.
  // if single thread pool, then don't need synchronous
  private synchronized void retrieveTokenAsync(){
    if(accessTokenInfo.isExpiringInDeltaTime(30000)) {
      asyncRetrievalInProgress.set(true);
      // fetch token and update.
      asyncRetrievalInProgress.set(false);
    }
  }

  class AccessTokenInfo {
    String accessToken;
    long expirationTimeMs;

    AccessTokenInfo(String accessToken, long expirationTimeMs){
      this.expirationTimeMs = expirationTimeMs;
      this.accessToken = accessToken;
    }

    public boolean isExpired() {
      return System.currentTimeMillis() > expirationTimeMs;
    }

    public boolean isExpiringInDeltaTime(long deltaTimeMs) {
      return (expirationTimeMs - deltaTimeMs) <= System.currentTimeMillis();
    }
  }
}