JDO Enhancement
Purpose
The JDO Enhancer does bytecode modifications on Java classes to make them persistence capable prior to loading them in the runtime. During the process of enhancement, the implementation of the javax.jdo.PersistenceCapable interface is added to the classes.
The automatic class enhancement is a convenient way of creating a JDO-aware application without having to implement the PersistenceCapable interface and all its methods manually. All you have to do is to provide the compiled Java classes and the JDO metadata.
Process Flow
The enhancement process is transparent to the application. The JDO enhancer is run before the application classes are loaded in the JVM (graphic 1).
Graphic 1: JDO Enhancement Process
The JDO enhancer applies changes to the classes to make them persistence capable. Among these changes are the following:
· Adding “implements PersistenceCapable” to the class definition;
· Appending the implementations of the methods from the PersistenceCapable interface;
· Adding accessor and mutator methods for the managed fields in the class;
· Declaring additional specific fields required for the classes that implement the interface – for example, a jdoStateManager field is added in the topmost class of the class hierarchy to establish the relation with the StateManager, which manages the values of the persistent fields and the life cycle of the persistent instances.
· Direct accesses to persistent fields are replaced by method calls, and so on.
On the basis of the information from the JDO metadata, the JDO Enhancer defines which fields are to be persistent. By default, all fields that are not declared final, static, or transient in the Java class become persistent, unless they are defined non-persistent in the metadata. For more information about field modifiers, see JDO Metadata.
To start the JDO Enhancer, you have to run its main class. The com.sap.jdo.enhancer.Main class is the implementation class of the JDO Enhancer. It is used as follows:
java com.sap.jdo.enhancer.Main <options> <jdofile> <classfile>
You can also use the following parameters:
JDO Enhancer Options
Option |
Description |
-h, --help |
Prints usage message and exits |
-v, --verbose |
Prints verbose messages |
-q, --quiet |
Supresses warnings |
-s, --sourcepath |
Source path for JDO and class files |
-d, --destdir <dir> |
Destination directory for output files |
-f, --force |
Overwrites output files |
-n, --nowrite |
Never writes output files |
-t, --timing |
Measures timing |
In addition, you can use the JDO Checker – a tool that checks the consistency of the classes to be enhanced.
The com.sap.jdo.sql.util.JDO class is the implementation of the JDO Checker. It is used as follows:
java com.sap.jdo.sql.util.JDO <options> <command> (<classfile>...|<class>...| tables <table>...)
JDO Checker Options
Option |
Description |
-h |
Prints usage message and exits |
-v |
Prints verbose messages |
-p |
Property file |
-c |
Catalog path |
JDO Checker Commands
Syntax |
CHECK <classfile> |
Arguments |
|
<classfile> |
The name of the file to be checked |
Description |
Checks mapping. |
Catalog/Checker Properties
Property |
Value |
com.sap.jdo.sql.mapping.checkCatalog |
TRUE |
com.sap.jdo.sql.mapping.checkConsistency |
TRUE |
com.sap.jdo.sql.mapping.checkConsistencyDeep |
TRUE |
See also:
Running the JDO Enhancer and Checker Tools