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Note that we again have to deal with JPA in two different environments: in plain Java SE and with EJBs in a Java EE environment. You may be more interested in one or the other when you read this section. We previously approached the subject of conversations with Hibernate by first talking about context propagation and then discussing long conversations. With JPA and EJB 3.0, we ll explore both at the same time, but in separate sections for Java SE and Java EE. We first implement conversations with JPA in a Java SE application without any managed components or container. We re often going to refer to the differences between native Hibernate conversations, so make sure you understood the previous sections of this chapter. Let s discuss the three issues we identified earlier: persistence context propagation, merging of detached instances, and extended persistence contexts.

Controlling the amount of information provided We stated that we want to reduce the amount of information provided when we invoke Ant. Getting rid of the [java] prefix is easy: we run the build file with the -emacs option; this omits the task-name prefix from all lines printed. The option is called -emacs because the output is now in the emacs format for invoked tools, which enables that and other editors to locate the lines on which errors occurred. When calling Ant from any IDE that lacks built-in support, the -emacs option may tighten the integration. For our exercise, we only want to change the presentation from the command line, which is simple enough:

Consider again the controller from listing 11.1. This code relies on DAOs that execute the persistence operations. Here is again the implementation of such a data access object with Hibernate APIs:

[secondbuild]$ ant -emacs execute Buildfile: build.xml init: compile: execute:

public class ItemDAO { public Bid getMaxBid(Long itemId) { Session s = getSessionFactory().getCurrentSession(); return (Bid) s.createQuery("...").uniqueResult(); } ... }

If you try to refactor this with JPA, your only choice seems to be this:

This leaves the next half of the problem, hiding all the output entirely. Three of the Ant options control how much information is output when Ant runs. Two of these (-verbose and -debug) progressively increase the amount. The verbose option is useful when you are curious about how Ant works, or why a build isn t behaving. The debug option includes all the normal and verbose output, and much more low level information, primarily only of interest to Ant developers. The -quiet option reduces the amount of information to a success message or errors:

public class ItemDAO { public Bid getMaxBid(Long itemId) { Bid maxBid; EntityManager em = null; EntityTransaction tx = null; try { em = getEntityManagerFactory().createEntityManager(); tx = em.getTransaction(); tx.begin(); maxBid = (Bid) em.createQuery("...") .getSingleResult(); tx.commit(); } finally { em.close(); } return maxBid; } ... }

This leaves us with no way of telling if the program worked, unless we can infer it from the time to execute. Would adding an <echo> statement in the execute target help Not by default. One of the attributes of echo is the level attribute: error, warning, info, verbose, and debug control the amount of information that appears. The default value info ensures that echoed messages appear in normal builds, or the two levels of even more information, verbose and debug. By inserting an echo statement into our execute target with the level set to warning, we ensure that even when the build is running in quiet mode the output appears. The Ant task declaration

No persistence-context propagation is defined in JPA, if the application handles the EntityManager on its own in Java SE. There is no equivalent to the getCurrentSession() method on the Hibernate SessionFactory. The only way to get an EntityManager in Java SE is through instantiation with the createEntityManager() method on the factory. In other words, all your data access methods use their own EntityManager instance this is the session-peroperation antipattern we identified earlier! Worse, there is no sensible location for transaction demarcation that spans several data access operations. There are three possible solutions for this issue:

Linux has similar capabilities with the davfs file system under development on SourceForge (http://dav.sourceforge.net/), and MacOS X supports DAV out of the box. WebDAV is nice as it runs through firewalls, talks straight to web servers, and, with digest authentication, always keeps your password safe. With HTTPS deployment, your documents are also kept private. One day Ant will support WebDAV out of the box, probably using the Jakarta Slide code, and then we can wave goodbye to <ftp>. When deploying with <copy>, consider setting overwrite="true". This forces Ant to copy the files you are installing over any that exist already, even if they are newer at their destination. If this flag is unset you cannot use Ant to roll back distributions, and some deployment actions (CD-based installation) can fail in obscure circumstances. Setting this flag does, of course, force Ant to overwrite any files that were updated on the server. If you are implementing persistence by saving data to files under your web application, you are already playing a dangerous game; <copy>