Arjun V. Bala Page 13

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1 7) What is Rmi? Give the Architecture of RMI and discussion the function of each layer. What is role of rmi Registry? (May-13,Jun-12,Nov-2011) The Java RMI is Java s native scheme for creating and using remote objects. Java RMI provides the following elements: 1. Remote object implementations. 2. Client interfaces, or stubs, to remote objects. 3. A remote object registry for finding objects on the network. A network 4. protocol for communication between remote objects and their client With RMI, you can get a reference to an object that lives in a remote process on remote hosts and invoke methods on it as if it were a local object running within the same Java virtual machine as your code. Each remote object implements a remote interface that specifies which of its methods can be invoked by clients. Arjun V. Bala Page 13

2 Description of the architecture: 1. The client uses the client-side stub to make a request of the remote object. The server object receives this request from a server-side object skeleton. 2. A client initiates an RMI invocation by calling a method on a stub object. 3. Marshaling involves converting local objects into portable form so that they can be transmitted to a remote process. 4. If the marshaling of method arguments succeeds, the client-side remote reference layer receives the remote reference and marshaled arguments from the stub. 5. The remote reference layer converts the client request into low-level RMI transport requests. 6. On the server, the server-side remote reference layer receives the transport-level request and converts it into a request for the server skeleton that matches the referenced object. 7. The skeleton converts the remote request into the appropriate method call on the actual server object. This involves unmarshaling the method arguments into the server environment and passing them to the server object. 8. If the method calls generates a return value or an exception, the skeleton marshals the object for transport back to the client and forwards it through the server reference layer. 9. The result is sent back using the appropriate transport protocol (e.g. Socket API using TCP/IP), where it passes through the client reference layer and stub, is unmarshaled by the stub, and is finally handed back to the client thread that invoked the remote method. RMI Registry The RMI Registry is a naming service. RMI server programs use this service to bind the remote java object with the names. Clients executing on local or remote machines retrieve the remote objects by their name registered with the RMI registry and then execute methods on the objects. RMI creates a remote proxy for that object and sent it to clients. An object proxy contains the reference to an object. Arjun V. Bala Page 14

3 8) what is JNDI? how it can be used for the for accessing various directory service such as LDAP,NIS,DNS?(Jan-13, Nov-11) A naming service assigns a standard name to a given set of data. This allows the application to access the objects remotely with the help of the name assigned to the object. A naming service allows tou to provide user-friendly names to object, such as address, identifiers, or objects typically used by computer programs. There are many directory and naming services available such as LDAP, NIS, DNS etc.. In our application we often need them to interact, but this directory services cannot interact with each other. To overcome this problem standard API, named JNDI is created, which allows to interact naming and directory services Here,are some well known directory : o LDAP (Lightweight Directory Access Protocol): A directory services protocol that enables clients to manage and query a hierarchical repository of entries and attributes. For example, LDAP can be used to locate information pertaining to users (e.g., X.509 certificates) and network resources (e.g., available printers). o NIS (Network Information System): A naming service, formerly known as yp, developed by Sun. It allows users to access systems on other hosts with a single user ID and password. o COS Naming Service: The CORBA naming service that enables CORBA clients to locate CORBA server objects using names. o DNS (Domain Name Service): A distributed naming service that allows users to refer to hosts using easily remembered names (e.g., arjun) instead of IP addresses. o javax.naming.ldap Classes and interfaces for using features that are specific to LDAP v3 that are not already covered by the more generic javax.naming.directory. 9) What is serialization of objects? Why do you need it? Give the example with necessary code. (Jan-13,Jun-12,Nov-11) Serialization is the process of saving an object in a storage medium (such as a file, or a memory buffer) or to transmit it over a network connection in binary form. The serialized objects are JVM independent and can be re-serialized by any JVM. In this case the "in memory" java objects state are converted into a byte stream. This type of the file can not be understood by the user. It is a special types of object i.e. reused by the JVM (Java Virtual Machine). Arjun V. Bala Page 15

4 This process of serializing an object is also called deflating or marshalling an object. The given example shows the implementation of serialization to an object. This program takes a file name that is machine understandable and then serializes the object. The object to be serialized must implement java.io.serializable class. class ObjectOutputStream extends java.io.outputstream implements ObjectOutput ObjectOutput interface extends the DataOutput interface and adds methods for serializing objects and writing bytes to the file. The ObjectOutputStream extends java.io.outputstream and implements ObjectOutput interface. It serializes objects, arrays, and other values to a stream. Thus the constructor of ObjectOutputStream is written as: ObjectOutput ObjOut = new ObjectOutputStream(new FileOutputStream(f)); Above code has been used to create the instance of the Object Output class with the ObjectOutputStream( ) constructor which takes the instance of the FileOuputStream as a parameter. Example: import java.io.*; public class serializedemo public static void main(string args[]) throws Exception myclass m=new myclass("parth",10); System.out.println("The object is: "+m); ObjectOutputStream o; o =new ObjectOutputStream(new FileOutputStream("d:\\1.txt")); o.writeobject(m); o.flush(); o.close(); ObjectInputStream i; i =new ObjectInputStream(new FileInputStream("D:\\1.txt")); myclass newobject=(myclass)(i.readobject()); i.close(); System.out.println("you have stored: "+newobject); static class myclass implements Serializable String name; int rollno; public myclass(string n,int r) this.name=n; this.rollno=r; public String tostring() return "name="+name +" and RollNo= "+rollno; Arjun V. Bala Page 16

5 10) Explain internationalization and its use using java (Jan-13,Nov-11) Internationalization is the process of designing an application so that it can be adapted to various languages and regions without engineering changes. Sometimes the term internationalization is abbreviated as i18n, because there are 18 letters between the first "i" and the last "n." An internationalized program has the following characteristics: 1. With the addition of localized data, the same executable can run worldwide. 2. Textual elements, such as status messages and the GUI component labels are not hardcoded in the program. Instead they are stored outside the source code and retrieved dynamically. 3. Support for new languages does not require recompilation. 4. Culturally-dependent data, such as dates and currencies, appear in formats that conform to the end user's region and language. 5. It can be localized quickly. Localization is the process of adapting software for a specific region or language by adding locale-specific components and translating text. The term localization is often abbreviated as l10n, because there are 10 letters between the "l" and the "n." The primary task of localization is translating the user interface elements and documentation. Localization involves not only changing the language interaction, but also other relevant changes such as display of numbers, dates, currency, and so on. Other types of data, such as sounds and images, may require localization if they are culturally sensitive. The better internationalized an application is, the easier it is to localize it for a particular language and character encoding scheme. Process of internationalizing the sample program: 1. Create the property files In the example the properties files store the translatable text of the messages to be displayed. Before the program was internationalized, the English version of this text was hardcoded in the System.out.println statements. The default properties file, which is called MessagesBundle.properties, contains the following lines: greetings = Hello farewell = Goodbye inquiry = How are you? Now that the messages are in a properties file, they can be translated into various languages. No changes to the source code are required. The French translator has created a properties file called MessagesBundle_fr_FR.properties, which contains these lines: greetings = Bonjour. farewell = Au revoir. inquiry = Comment allez-vous? 2. Define the Locale The Locale object identifies a particular language and country. The following statement defines a Locale for which the language is English and the country is the United States: alocale = new Locale("en","US"); The next example creates Locale objects for the French language in Canada and Arjun V. Bala Page 17

6 in France: calocale = new Locale("fr","CA"); frlocale = new Locale("fr","FR"); 3. Create a ResourceBundle ResourceBundle objects contain locale-specific objects. You use ResourceBundle objects to isolate locale-sensitive data, such as translatable text. In the sample program the ResourceBundle is backed by the properties files that contain the message text we want to display. The ResourceBundle is created as follows: messages = ResourceBundle.getBundle("MessagesBundle", currentlocale); The arguments passed to the getbundle method identify which properties file will be accessed. The first argument, MessagesBundle, refers to this family of properties files: MessagesBundle_en_US.properties MessagesBundle_fr_FR.properties MessagesBundle_de_DE.properties The Locale, which is the second argument of getbundle, specifies which of the MessagesBundle files is chosen. When the Locale was created, the language code and the country code were passed to its constructor. 4. Fetch the Text from the ResourceBundle The properties files contain key-value pairs. The values consist of the translated text that the program will display. You specify the keys when fetching the translated messages from the ResourceBundle with the getstring method. For example, to retrieve the message identified by the greetings key, you invoke getstring as follows: String msg1 = messages.getstring("greetings"); Arjun V. Bala Page 18