3. Part I: Simple Object Persistence

This part of the project is to be implemented individually.

You will be implementing an object-oriented database: that is, all of the data will be stored as Java objects. As you know, Java objects are not normally persistent: they disappear when the execution environment terminates.

In order to use Java objects as a database, you will have to somehow make them persistent. In this assignment, you will do this in two different ways.

• Part A: Storing and Retrieving Objects from an XML file


One approach to object persistence is to store the objects in some encoded-text form. XML provides a reasonable framework for doing this, with a simple tag-pair and parameter syntax. I have written a Java class that will read in an object description in a simple XML-structured file and return the parsed results in a collection of objects that may be easily traversed to create a new instance of the object described by the XML. I have also written an example program showing how to use the XML parser to reconstruct objects from the parsed descriptions.

Here is a simple object class for storing customer information:

   public class Customer
     {
       public String name;           // Customer name
       public String address;        // Customer address
       public Vector phoneNumbers;   // Contains String objects
     }

We need a place to put all of the customers:

   public class Database
     {
       public Vector customers;    // Contains Customer objects
     }

  Here is the tar file with everything in it. Please use this:

• proj1.tar

  Here is the example code:

• ParseXMLObjs.java
• ParseTest.java

  Here is a test dataset to use with the example code:

• example1.xml

 

1.

For the Java classes given above, implement the method setValuesFromXML() that sets the field values from the parsed XML data structure, for each class.

2.

For the Java classes given above, implement the method writeXML() that writes out the entire object in the XML form that can be read back by ParseXMLObjs.

3.

For the Java classes given above, implement a toString() method that prints out the values of the fields in the object in a reasonable way.

4.

For the following customers, create an XML file encoding the objects that represent these customers. Be sure to create the database object that contains these objects as well! Write a program that reads the and creates the objects from the file. Show that your program works by printing out the objects using the toString() method.

       John Smith; 123 Main St, New Brunswick, NJ; 555-1223, 555-1234
       June Allen; 112 New St, Piscataway, NJ; 555-2212
       Robert Jones; 121 First St, So. Plainfield, NJ; 555-1919, 555-3333, 555-2231
       Julie Patel; 443 Last Rd, Washington, NJ; 555-9233

5.

Modify your program to have it write out the objects to a new XML file. Show that your program works by running it and printing out the resultant XML file.

• Part B: Lightweight Persistence


Java provides a method for storing and retrieving objects using so-called ``lightweight persistence''. Here is an example of this from the Eckel book, chapter 10:

• Worm.java

1.

Modify your program from Part A to read in objects from either an XML file or a file created by writing out the objects with lightweight persistence.

2.

Modify your program from Part A to write out objects to either an XML file or use lightweight persistence to write them to a file.

3.

Demonstrate that your program works by writing and subsequently re-loading the objects from Part A using lightweight persistence.

2002-02-12