Tag: javaee6

I recently posted a screencast showing how a simple JavaEE 6 web application can take advantage of Java 7’s new language features (aka project coin). Here are more details on the code for the three Java 7 new language features shown. The full code is available here.

The first Project Coin feature shown (Java 7 refactorings start at 7:37 into the screencast) is Strings in switch statements. This is rather straightforward (a number of folks thought this was already supported) and if probably a good candidate to use with web frameworks which take user input as Strings.


String name = request.getParameter("name");
if ("duke".equals(name)) {
    vip = true;
    name = name.toUpperCase(); // let's visually recognize DUKE
} else if ("sparky".equals(name)) {
    vip = true;         // another VIP
}


becomes :


String name = request.getParameter("name");
switch (name) {
    case "duke":
        vip = true;
        name = name.toUpperCase(); // let's visually recognize DUKE
        break;
    case "sparky":
        vip = true;         // another VIP
        break;
}


Of course you can also have a default: section equivalent to an else statement.

The second feature is try-with-resources and is shown here in the initializing sequence of a stateless EJB. It uses JDBC to ping a well-known system table. The code specifically relies on the fact that multiple classes in JDBC 4.1 (Connection, Statement and ResultSet) now implement the new Java 7 java.lang.AutoCloseable interface. This is what allows for the following code requiring proper closing of resources :


@PostConstruct
public void pingDB(){
    try {
        Connection c = ds.getConnection();
        Statement stmt = c.createStatement();
        ResultSet rs = stmt.executeQuery("SELECT * from SYS.SYSTABLES");
        while (rs.next()) {
            System.out.println("***** SYSTEM TABLES" + rs.getString("TABLENAME"));
        }
        stmt.close();
        c.close();
    } catch (SQLException ex) {
        ex.printStackTrace();
    }
}


… to be rewritten as follows (resources initialized in a single statement, no closing required as the compiler takes care of it when they go out of scope) :


@PostConstruct
public void pingDB() {
    try (Connection c = ds.getConnection(); Statement stmt = c.createStatement()) {
        ResultSet rs = stmt.executeQuery("SELECT * from SYS.SYSTABLES");
        while (rs.next()) {
            System.out.println("***** SYSTEM TABLES" + rs.getString("TABLENAME"));
        }
    } catch (SQLException ex) {
        ex.printStackTrace();
    }
}


As you can see in the source code, the DataSource is actually created using a @DataSourceDefinition annotation which is a new feature in Java EE 6.

The third and final part of the demonstration uses a somewhat convoluted piece of JPA code to illustrate the multi-catch feature. For the purpose of the demo, the JPA query (also in the above EJB) uses a LockModeType.PESSIMISTIC_WRITE (new in JPA 2.0) when building the JP-QL query and adds two catch blocs for PessimisticLockException and LockTimeoutException :


try {
    List customers = em.createNamedQuery("findAllCustomersWithName")
        .setParameter("custName", name)
        .setLockMode(LockModeType.PESSIMISTIC_WRITE)
        .getResultList();
    if (customers.isEmpty()) {
        doesExist = false;
        Customer c = new Customer();
        c.setName(name);
        em.persist(c);
    } else {
        doesExist = true;
    } catch (final PessimisticLockException ple) {
        System.out.println("Something lock-related went wrong: " + ple.getMessage());
    } catch (final LockTimeoutException lte) {
        System.out.println("Something lock-related went wrong: " + lte.getMessage());
    }

}


Which can be refactored to this equivalent code using multi-catch :


try {
    List customers = em.createNamedQuery("findAllCustomersWithName")
        .setParameter("custName", name)
        .setLockMode(LockModeType.PESSIMISTIC_WRITE)
        .getResultList();
    if (customers.isEmpty()) {
        doesExist = false;
        Customer c = new Customer();
        c.setName(name);
        em.persist(c);
    } else {
        doesExist = true;
    } catch (final PessimisticLockException | LockTimeoutException ple) {
        System.out.println("Something lock-related went wrong: " + ple.getMessage());
    }


}


This new language feature is *very* useful for reflection or java.io File manipulation, not quite the most common Java EE code out there.

Of course all of the above only works with JDK 7 at runtime and if running NetBeans 7.0.1 you’ll also need to set the source level to Java 7 for the quick fixes to light up. I’ve also successfully executed this under Mac OS X using the OpenJDK Mac OS binary port.

Some resources :

• Full Source code.
• Screencast showing this “in action”.
• String in switch statements.
• try-with-resources.
• Multi-catch and precise rethrow.