CODEWITHSUNDEEP
java
user840930
user840930

Reputation: 5578

how to make object accessible to another object deep in the code?

in java, I am reading from a property file into a Properties object:

  static Properties fileProp = null;  // holds file properties
  public static void main( final String[] args ) throws IOException 
  {
     ...
    //load a properties file
    InputStream is = LearnButtonPressHttpHandler.class.getResourceAsStream("/rsrc/file.properties");

    fileProp.load(is);
    ...

    // more objects are created

  }

later, deeper into the code, several layers deeper, I need to access this properties object but find that I don't have access to this fileProp object. I don't want to pass this object as a parameter down the many layers to where I need it. It would solve the problem but does not seem to be such an elegant solution. Is there a better way?

Upvotes: 3

Views: 98

Answers (4)

Satheesh Cheveri
Satheesh Cheveri

Reputation: 3679

Create Singleton class which performs the property loading( I prefer Singleton rather than static class). Then you can access properties from any where.

public class Singleton {
    private static  Singleton INSTANCE = null;
    Properties props = new Properties();
    public static final Singleton getInstance() throws IOException {
         if (INSTANCE == null) {
             synchronized (Singleton.class) {
                 if (INSTANCE == null) {
                     INSTANCE = new Singleton();
                     INSTANCE.loadProperties();
                 }
             }
         }
        return INSTANCE;
    }
    private  void  loadProperties() throws IOException{
          InputStream is = Singleton.class.getResourceAsStream("/rsrc/file.properties");
          props.load(is);
    }
    public Object getData(String key){
        return props.get(key);
    }
}

Upvotes: 1

amphibient
amphibient

Reputation: 31238

The simplest way in plain Java is to use the Singleton pattern, load your properties singleton at application startup or have a getProperties method in that class that returns the properties if they have been loaded and load them if not.

For example:

public class MySingleton {
   private static MySingleton instance = null;
   protected MySingleton() {
      // Exists only to defeat instantiation.
   }
   public static MySingleton getInstance() {
      if(instance == null) {
         instance = new MySingleton();
         instance.loadData()
      }
      return instance;
   }

   private void loadData(){
      //doSomething
   }
}

In this case, you can call MySingleton.getInstance(), and that will get you the data object that you want and not reload it if it was previously loaded. If it is the first time, it will load it lazily.

If you are using a framework or an application server, there is a multitude of ways depending on what your stack offers. E.g. in Spring, singleton is the default bean type.

Upvotes: 1

Rob
Rob

Reputation: 11733

This is one of the major things dependency injection does. For instance, in Spring there is a PropertyPlaceholderConfigurer that is used to inject properties from one place into beans as they are being constructed (cf. the Prototype Pattern in Gang of Four).

Many frameworks just do static property management, e.g. Play. Then you are basically implementing a Singleton.

Upvotes: 0

Mad Physicist
Mad Physicist

Reputation: 114320

Create a static getter for the fileProp reference:

public static Properties getFileProp()
{
    return fileProp;
}

This way, any other piece of code that needs it, can access it.

Upvotes: 1

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