Getting Access To Private Fields in JAVA using Reflection:

Getting Access To Private Fields in JAVA using Reflection:



Private fields are... ehem, private, that means that they cannot (should not) be known, inspected or changed... now that inversion of control is common around us, what if a class is keeping a field private to protect it from 'abuse' but I want to access it just to abuse it softly (??? I should check my semantics when talking about code). What if I want Inversion of Control and I do not have an IOC Container? Ok, lets do it the hard (O_O ???) way.

For example, a Business Object is keeping a Data Object in private for it not to be directly used out of the Business Tier, but a Manager class wants to be made responsible for Business Tier's persistence. So the manager takes the Business Object, takes its DataObject, and persists it... but, it cannot! the Data Object was set to... private.

Ok, here is how to change that field access permissions during runtime:

Obtain a private field and play with it:   

        BusinessEntity businessEntity=... //The business object we are working with;
        DatabaseEntity databaseEntity;
        //_databaseEntity is the private field we want to play with.
        Field f = businessEntity.getClass().getDeclaredField("_databaseEntity"); 
        f.setAccessible(true);
        databaseEntity = (DatabaseEntity) f.get(businessEntity); //IllegalAccessException
        f.setAccessible(false);
        getDataTier.persist(databaseEntity);

Use it with caution, it is good it can be done, but may result in awful designs if not handled properly (you risk addicted).


   

Comments

Post a Comment

Popular posts from this blog

Qt Signals and Slots, Connecting and Disconnecting

Image
Slots, slots everywhere... by Ramon Talavera Qt connects widgets by means of a nice designed scheme based on the idea that objectS may send signalS of different typeS to a single object instance: This is a screenshot of the example code running. The main application creates dialogs A and B and then connects the signal from A to the signal slot in B. I cannot believe I have clicked it 100 times to show you that it works... Declaring the signal:  A declares to be able to send signals of type ' somebodyClicked ': class ObjectADialog : public QDialog { Q_OBJECT public: explicit ObjectADialog(QWidget *parent = 0); ~ObjectADialog(); signals:      void somebodyClicked(QString who); protected: void closeEvent(QCloseEvent *event); private slots: void on_pushButton_clicked(); private: Ui::ObjectADialog *ui; }; Declaring the slot: B declares to contain a slot method for signals to connect to:   class ObjectBDialog : public QDialog
Read more

Vaadin 7: Detect Enter Key in a TextField

Vaadin 7: Detect Enter Key in a TextField This can be easily achieved just by adding a shortcutlistener whenever the TextField gets the focus and remove it when it blurs. From an IOC perspective wrapping the TextField would most probably result in less rework than extending the TextField: For example: TextField myTextField = new TextField("A text field"); myTextField.setImmediate(true); OnEnterKeyHandler onEnterHandler=new OnEnterKeyHandler(){             @Override             public void onEnterKeyPressed() {                  Notification.show("V oight Kampff Test ",                     Notification.Type.HUMANIZED_MESSAGE);             }         }; onEnterHandler.installOn(myTextField); ------------------------------------------------------------------- And the code for OnEnterKeyHandler is: import com.vaadin.event.FieldEvents; import com.vaadin.event.ShortcutAction; import com.vaadin.event.ShortcutListener; import com.vaadin.ui.TextField; p
Read more

JAVA JPA WITH HIBERNATE AND H2 Tutorial

Image
JAVA JPA WITH HIBERNATE AND H2 Tutorial Setting the environment: Download and install H2 Database http://www.h2database.com/html/download.html Create a connection to the database, in my case I am using Netbeans. Creation of a new Database Connection can be done from the Services Tab, Databases node: Have in mind that it is not possible to test the connection before the JDBC URL has been written into. Select the PUBLIC schema when asked. And put a name onto it, I decided to name it as "Hibernate 101 on H2" Download Hibernate http://sourceforge.net/projects/hibernate/files/hibernate3/ JPA with Hibernate: For the shake of portability and standarization we will be using JPA. Natively speaking, Hibernate relies onto a context configuration file -  hibernate.cfg -  and a single or many persistence configuration files  - hibernate.hbm.xml - .  On the other hand JPA configuration is based on just one file:  persistence.xml.  Netbeans offe
Read more