CS 185C/286 - Lecture 17

Cay S. Horstmann

Lecture 17 Quiz 1

No quiz. But I'll check the reading in the final exam.

Today's Lecture/Lab

• Server-side programming
• Java EE in 15 minutes

Java EE for Elvis

• Standard Java approach for web applications
• Greatly simplified in EE5, EE6
• Robust, scalable server technology (transactions, clustering, etc. without additional programming)
• Why Elvis? Google for Mort Elvis Einstein

Java EE Architecture

• User interface: JSF pages, HTML 5, mobile device
• Business logic: Session beans
• Persistence: Entity beans
• Bean = class with default constructor and properties (getters/setters)

Java Persistence Architecture (JPA)

• Stores Java entity classes in SQL databases
• Annotate class with @Entity
• Supply ID field and annotate with @Id @GeneratedValue
• Annotate relationships with @OneToMany etc.

  import javax.persistence.*;
  @Entity public class Question implements Serializable {
      @Id @GeneratedValue private int id;
      private String text;
      @OneToMany private Set<Choice> choices;
      public Question() {} // No-arg constructor is required          
      ...
  }

• Stored in a table with columns id, text
• CHOICE table has foreign key for quiz ID

Entity Manager

• Persistence context = set of managed entities
• Entity manager = object that manages persistence context (has methods persist, find, createQuery, ...)
• JPQL = object-oriented persistence query language

  EntityManager em = ...; // see next slide
  Query q = em.createQuery("SELECT x FROM Quiz x WHERE x.id = :id")
      .setParameter("id", id);
  Quiz p = (Quiz) q.getSingleResult(); // Also fetches questions (maybe lazily)

• Here are more sample JPA queries

Session Beans

• Entity manager can only be accessed by “session beans”
• Stateless session bean has “do and forget” methods; similar to a class with only static methods
• Methods are automatically transactional (serialized, roll back on errors)
• Entity manager injected into session bean

  @Stateless
  public class UserSB {
      @PersistenceContext private EntityManager em;
      ...
  }

• “injected” means that the field is set by the container when the bean is constructed

Reading Before Next Class

• Chapter 4 in the Java EE Pocket Guide

Lab

The Entities

• A quiz has questions. Questions have choices.
• 
• Basic Java classes:

  public class Choice { 
     private String text; 
  
     public Choice(String text) { this.text = text; }   
     public String getText() { return text; } 
  }
  
  public class Question { 
     private String text; 
     private Set<Choice> choices = new HashSet<>(); 
     private String answer; 
     
     public Question(String text) { this.text = text; }
  
     public String getText() { return text; } 
     public String getAnswer() { return answer; } 
     public void setAnswer(String answer) { this.answer = answer; } 
     public Collection<Choice> getChoices() { return choices; } 
  }
  
  public class Quiz {
     private Set<Question> questions = new HashSet<>();
  	
     public Set<Question> getQuestions() { return questions; }
  }         
  

• Turn these into entity classes.

Initializing the Data

• Normally, this part is done differently. Here, we just do it ad-hoc and in a rather un-RESTful way.
• Start GlassFish and run

  ~/glassfish-3.1.2.2/bin/asadmin start-database

• Build a WAR file testbank.war with
  • this file
  • Your entity classes
  • The (suitably modified) AppConfig from last lab
  • This file in WEB-INF/classes/META-INF/persistence.xml
• After compiling and deploying, point your browser to http://localhost:8080/testbank/rest/quiz/init
• What happens?
• Write down that number. You'll need it later.

Spying on the Database

• Make a file ij.properties with this contents:

  ij.driver=org.apache.derby.jdbc.ClientDriver
  ij.protocol=jdbc:derby://localhost:1527/
  ij.database=sun-appserv-samples;create=true

  Run the command

  java -jar ~/glassfish-3.1.2.2/javadb/lib/derbyrun.jar ij -p ij.properties

  Then run the commands

  select * from quiz;
  select * from question;
  select * from quiz_question;

  Explain the role of the quiz_question table.
• exit; gets you out of ij.

Client Queries

• Declare a JAX-RS method that lets us query for all questions in a quiz with a given ID as http://localhost:8080/testbank/rest/quiz/question/129, where the last part is the quiz id, revealed by the /init command. What is the method header?
• The query that you need to make is

  Query query = em.createQuery(
     "SELECT q FROM Quiz z, IN(z.questions) q WHERE z.id = :id")
     .setParameter("id", id);
  @SuppressWarnings("unchecked")
  List<Question> questions = query.getResultList();
  

  You get a list of matching questions. Generate a string that contains, for each question, the question ID and a newline.
• What is the significance of the SuppressWarnings annotation? (Try compiling without it.)
• Compile and deploy, then point your browser to the URL given above, where you use the ID number of the quiz that you got from two slides ago.
• What happens?
• Enhance your output and add the question text after each ID. How did you do that?
• Now implement a query that lists all choice texts for a given question ID. For example, http://localhost:8080/testbank/rest/quiz/question/105 might yield

  run anywhere
  debug everywhere
  run many times
  read anywhere

  How did you do that?