c# create and print barcode Merge points in Java

Maker Quick Response Code in Java Merge points

Perhaps a new version of Hibernate is released that defines a new property mapping that XDoclet doesn t support yet. You don t want to handwrite the entire .hbm.xml file just the single property. The most

common solution for this problem is to use XDoclet s built-in merge feature. Since you shouldn t hand-edit actively generated code,6 XDoclet lets you inject handwritten code into the final actively generated file. XDoclet refers to these as merge points. The Hibernate module supports injecting handwritten XML configuration into each hbm.xml file. If you look at the generated Event.hbm.xml file, you should see a helpful comment that looks like this:

<!-- To add non XDoclet property mappings, create a file named hibernate-properties-Event.xml containing the additional properties and place it in your merge dir. -->

This tells you that if you write a file called hibernate-propertiesEvent.xml and put it in the magical merge directory, XDoclet will insert it in the finished Event.hbm.xml file. Suppose, for example, you didn t have access to the Address object. You cannot insert XDoclet tags to nicely generate the component mapping. Instead, you have to include a handwritten component mapping and merge it into the Location.hbm.xml file. Create a directory named /work/calendar/src/xdt. This will be your merge directory, where your handwritten merge files will go. Then create a file called hibernate-properties-Location.xml in the merge directory. One tricky thing is that the directory structure where the merge file is needs to match the package structure of the class. In this case, create a directory structure that looks like /work/calendar/src/xdt/com/ manning/hq/ch09. The hibernate-properties-Location.xml file goes in that directory. Here s what the file should contain:

Actively generated code can be automatically regenerated at any time and therefore should not be hand-edited since changes will be lost. This is opposed to passively generated code, which is generated once, and then modified, edited, and checked into source control like any source file would be. All the examples from this chapter have featured active generation.

<component name="address" class="com.manning.hq.ch09.Address" > <property name="streetAddress" type="java.lang.String" column="street_address" /> <!-- Other properties omitted --> </component>

Next, you need to modify the hibernatedoclet task in Ant so that it knows where the merge directory is. Make the following modification to the build9.xml file:

This tells XDoclet to use the relative directory of src/xdt as the merge directory. Finally, since you do actually have control over the Address source file, you want to modify Location s address property. Otherwise, you would have two properties generated, one by XDoclet and one from the merge file. Modify the getAddress() method and remove the @hibernate.component tag as shown here:

/** * Mapping handled by hibernate-properties-Location.xml */ public Address getAddress() { return address; }

At this point, rerun the generate-hbm task. Inspect the Location.hbm.xml file and you should see that the component fragment has been inserted, and the merge comment will be gone.

The primary way Ant can be customized for different deployment environments is by the use of properties. XDoclet builds on this by allowing the use of Ant properties inside an XDoclet tag. Suppose you want

to customize the key-generation algorithm for different database deployments. In one case, you want to use hilo, and in another, identity. You ll need two targets in your Ant build.xml, one for each environment that sets the property accordingly:

<target name="generate-identity"> <property name="hibernate.id.value" value="identity"/> <antcall target="generate-hbm"/> </target> <target name="generate-hilo"> <property name="hibernate.id.value" value="hilo"/> <antcall target="generate-hbm"/> </target>

Calling one target or the other will set the Ant property for that environment; it then regenerates the mapping files. Next you need to modify the Event class to make the @hibernate.id tag dynamic:

/** * @hibernate.id generator-class="${hibernate.id.value}" * column="uid" */ public Long getId() { return id; }

Here you have basically inserted an Ant property directly into the XDoclet tag. You can do this for any XDoclet property as well, so there are a huge number of possibilities. It lets you move the details out of the Java classes (where some developers may not want to put things such as table or column names) and into Ant, which can be tweaked for different environments. Run the generate-hilo target. If all has gone well, when you inspect the Event.hbm.xml file you should see something like this fragment: