On Dec 22, 2008, at 1:56 AM, Ilan Kirsh wrote:
Resource names and class names are not the same.
Right. What the enhancer operates on is the byte code representation
of files, not the classes as loaded by a class loader. With that
distinction in mind, what the enhancer needs access to is either the
file name from which it can open a file, or the resource name which it
can ask the class loader to open as a stream.
Is class name supported?
That's an open question in my mind. How would you propose that the
enhancer find the file corresponding to the class?
1. The class loader might not want to give you access to the file,
especially for example if it was loaded from a jar. In that case, what
you need is the path to the jar or the resource name of the jar.
2. As far as I know, there's no reverse translation of class loader +
class name to file name.
(myPackage.* might also be supported).
Right; keeping in mind that the shell might resolve the "*" wild card,
you may have to quote it.
Craig
----- Original Message ----- From: "Craig L Russell" <[email protected]
>
To: "JDO Expert Group" <[email protected]>; "Apache JDO
project" <[email protected]>
Sent: Monday, December 22, 2008 1:41 AM
Subject: Enhancer specification text for discussion
I thought at this point it would be useful to discuss the
specification, which should resolve the remaining API issues. I
still need to add the enhancer API itself but want to wait until
we all agree on the description of the utility.
<proposed>
Add to 23.1 Overview:
A command line tool to invoke a byte code enhancer is standard
with JDO 2.3. The tool is distributed as part of the specification
jar. The tool analyzes command line arguments and passes control
to an implementation-provided class to perform the enhancement of
classes. The tool locates the implementation-provided class using
the services locator architecture.
Add to 23.2 Goals:
Support for static enhancement of classes by a tool run after
compilation but before execution
Support for dynamic enhancement of static (compiled with javac) and
dynamic (created at runtime) classes by user- or implementation-
written class loader
Support for build tools such as maven plugins, eclipse plugins,
and ant plugins
Insert before 23.3 Enhancement: Architecture:
23.3 Standard Enhancement
The enhancement process consists of two distinct functions:
analyzing user input as to how and what to enhance; and performing
the enhancement of the persistent classes. A Java main program is
distributed as part of the java specification jar. Plugins for
Interactive Development Environments are expected by the
architecture but not provided by the JDO specification jar itself.
Enhancing the persistent classes is the function of a JDO
implementation, and in particular, the Reference Implementation.
The Enhancer main program calls a standard enhancer by using the
services locator architecture. Thus, the Enhancer main program can
call any enhancer provided by a JDO implementation and made
available on the class path.
The enhancer operates on the byte code representation of persistent
classes, and creates new byte code representations of the classes.
The input byte code representations can come from four sources:
a byte array such as might be created by a dynamic class generator;
a file that contains the byte codes as generated by the javac
compiler;
a jar file containing multiple classes and metadata files;
a resource loaded from a class loader that contains the byte codes
as generated by the javac compiler
The output byte code representations can be written to one of three
destinations:
the same file as was provided as input;
the same jar file as was provided as input, in which case all
contents of the jar file that are not enhanced are preserved intact;
a directory that contains package names as directory names with
identical semantics to the javac compiler's output directive.
Restrictions: if a resource is used as input, then the only output
possible is a directory. If a class file or jar file is used as
input, the file must be read/write. If a byte array is used as
input, then the enhanced byte array is available via a separate
method call and is not written to output.
23.3.1 Enhancer Main
The Enhancer main class is intended to be run from an interactive
shell (command line). It analyzes arguments and delegates to an
implementation. The implementation must be identified via an entry
in the class loader's resource file META-INF/services/
javax.jdo.JDOEnhancer. If multiple such files exist, the Enhancer
main uses the first file containing the name of a class that can
be loaded by the Class.forName method, containing a public no-args
constructor, that returns an instance that implements
javax.jdo.JDOEnhancer.
The enhancer is invoked with the following command line:
java -cp <classpath> javax.jdo.Enhancer <options> <directory, file,
or resource names>
<classpath> must contain the jdo specification jar, the
implementation jar and any implementation dependencies, the
statically-compiled classes, and the jdo metadata files loadable
as resources
<options> include:
-pu <persistence-unit-name> : the name of a persistence unit
-d <target directory> : write the enhanced classes to the specified
directory
-checkonly : just check the classes for enhancement status
-v : verbose output
-r : recurse through directories to find all classes and metadata
files to enhance
-cp <enhancer class loader path> : if not already included in the
java class loader, this parameter must contain the statically-
compiled classes, and the jdo metadata files loadable as resources
<directory, file, or resource names>
each entry following the options must be a directory, a file, or a
resource name.
The enhancer main program processes the command line and passes the
parameters to the enhancer found via services lookup.
Parameters are processed until the first non-option parameter is
found. All subsequent parameters are treated as directory, file,
or resource names. Parameters beginning with "-" are considered to
be options. If an option is not a standard option, it is added to
the non- standard options list. If a non-standard option is not
recognized, it is [[[expert group choice here: ignore it or throw
an exception]]].
Parameters are processed as follows:
-cp <enhancer class loader path>: If this option is present, a new
class loader is constructed, parented with the context class
loader, to which the urls in the <enhancer class loader path> are
added. The format of <enhancer class loader path> is the same as
the -cp option of the java command. The class loader is passed to
the enhancer via the setClassLoader method.
-pu <persistence-unit-name>: If this option is present, each
persistence-unit-name is passed to the enhancer via the
addPersistenceUnit method.
-d <target directory>: If this option is present, the target
directory is passed to the enhancer via the setOutputDirectory
method.
-v: If this option is present, the verbose flag is set via the
setVerbose method.
-r: If this option is present, the recurse flag is set via the
setRecurse method.
-checkonly: If this option is present, the files are not enhanced,
but verified via the validate method. If this option is absent, the
files are enhanced via the enhance method.
-<option>: If a parameter begins with a "-" is found, it is added
to the other options list via the addOptions method.
Parameters that follow the last option are passed to the enhancer
via the setFiles method. The enhancer handles the files as follows:
For a directory, the contents of the directory are analyzed
for .class, .jdo, and .orm files which are then treated as if they
were passed directly, as directory/*.class directory/*.jdo
directory/ *.orm. If the -r option is specified, each subdirectory
of the directory is treated as if it were itself the directory
parameter. Thus, every .class file, .jdo file, and .orm file in
the directory are included as files for enhancement.
For a .class file, the file must contain the byte codes of a
persistent class consistent with the file name. Metadata is found
using the algorithm detailed in Chapter 18, using the path
specified for the .class file and recursing through parent
directories in the file system.
For a .jdo or .orm file, the file must be a valid metadata file
and the classes described in the file are treated as described
(persistence-capable, persistence-aware, or not persistent).
Metadata is found using the algorithm detailed in Chapter 18.
For a .jar file, the file must contain .class files and the
corresponding .jdo and .orm metadata files.
If the parameter is not able to be resolved as a directory or file,
it is assumed to be a resource name that is loadable via the class
loader constructed using the enhancer -cp parameter. If there is no
-cp parameter then the context class loader is used. The resource
name names a .class file, a .jdo file, or .orm file, and the
treatment of these resources is the same as if they were files
found in the file system.
</proposed>
Craig L Russell
Architect, Sun Java Enterprise System http://db.apache.org/jdo
408 276-5638 mailto:[email protected]
P.S. A good JDO? O, Gasp!
Craig L Russell
Architect, Sun Java Enterprise System http://db.apache.org/jdo
408 276-5638 mailto:[email protected]
P.S. A good JDO? O, Gasp!
