idlj - The IDL-to-Java Compiler

idlj generates Java bindings from a given IDL file.

Synopsis

idlj [ options ] idl-file
Options may appear in any order, but must precede the idl-file.

Description

The IDL-to-Java Compiler generates the Java bindings for a given IDL file. For binding details, see the IDL to Java document at the OMG website.

Emitting Client and Server Bindings
To generate Java bindings for an IDL file named My.idl:
idlj My.idl
This generates the client-side bindings and is equivalent to:
idlj -fclient My.idl
The client-side bindings do not include the server-side skeleton. If you want to generate the server-side bindings for the interfaces:
idlj -fserver My.idl
Server-side bindings include the client-side bindings plus the skeleton, all of which are ImplBase (that is, Inheritance model) classes. If you want to generate both client side and server side bindings, use one of the following (equivalent) commands:
idlj -fclient -fserver My.idl
idlj -fall My.idl
The default server-side model is the inheritance model. Given an interface My defined in My.idl, the file _MyImplBase.java is generated. You must provide the implementation for My and it must inherit from _MyImplBase.
There is another server-side model called the Tie Model. This is a delegation model. The following commands generate the bindings for the Tie Model:
idlj -fserverTIE My.idl
idlj -fallTIE My.idl
For the interface My, this will generate My_Tie.java. The constructor to My_Tie takes a My. You must provide the implementation for My, but it does not have to inherit from any other class, only the interface My. But to use it with the ORB, you must wrap your implementation within My_Tie. For instance:
MyImpl myImpl = new MyImpl ();
My_Tie tie = new My_Tie (myImpl);
orb.connect (tie);
You might want to use the Tie model instead of the typical Inheritance model if your implementation must inherit from some other implementation. Java allows any number of interface inheritance, but there is only one slot for class inheritance. If you use the inheritance model, that slot is used up . By using the Tie Model, that slot is freed up for your own use. The drawback is that it introduces a level of indirection: one extra method call occurs when invoking a method.
Specifying Alternate Locations for Emitted Files
If you want to direct the emitted files to a directory other than the current directory, invoke the compiler as:
idlj -td /altdir My.idl
For the interface My, the bindings will be emitted to /altdir/My.java, etc., instead of ./My.java.
Specifying Alternate Locations for Include Files
If My.idl included another idl file, MyOther.idl, the compiler assumes that MyOther.idl resides in the local directory. If it resides in /includes, for example, then you would invoke the compiler with the following command:
idlj -i /includes My.idl
If My.idl also included Another.idl that resided in /moreIncludes, for example, then you would invoke the compiler with the following command:
idlj -i /includes -i /moreIncludes My.idl
Since this form of include can become irritatingly long, another means of indicating to the compiler where to search for included files is provided. This technique is similar to the idea of an environment variable. Create a file named idl.config in a directory that is listed in your CLASSPATH. Inside of idl.config, provide a line with the following form:
includes=/includes;/moreIncludes
The compiler will find this file and read in the includes list. Note that in this example the separator character between the two directories is a semicolon (;). This separator character is platform dependent. On NT it is a semicolon, on AIX it is a colon, etc.
Emitting Bindings for Include Files
By default, only those interfaces, structs, etc, that are defined in the idl file on the command line have Java bindings generated for them. The types defined in included files are not generated. For example, assume the following two idl files:

My.idl

#include <MyOther.idl>
interface My
{
};

MyOther.idl
interface MyOther
{
};

The following command will only generate the java bindings for My:
idlj My.idl
To generate all of the types in My.idl and all of the types in the files that My.idl includes (in this example, MyOther.idl), use the following command:
idlj -emitAll My.idl
There is a caveat to the default rule. #include statements which appear at global scope are treated as described. These #include statements can be thought of as import statements. #include statements which appear within some enclosing scope are treated as true #include statements, meaning that the code within the included file is treated as if it appeared in the original file and, therefore, Java bindings are emitted for it. Here is an example:

My.idl

#include <MyOther.idl>
interface My
{
#include <Embedded.idl>
}; MyOther.idl

interface MyOther
{
}; Embedded.idl

enum E {one, two, three};

Running the following command:
idlj My.idl
will generate the following list of Java files:
./MyHolder.java
./MyHelper.java
./_MyStub.java
./MyPackage
./MyPackage/EHolder.java
./MyPackage/EHelper.java
./MyPackage/E.java
./My.java
Notice that MyOther.java was not generated because it is defined in an import-like #include. But E.java was generated because it was defined in a true #include. Also notice that since Embedded.idl was included within the scope of the interface My, it appears within the scope of My (that is,in MyPackage).
If the -emitAll flag had been used in the previous example, then all types in all included files would be emitted.
Inserting Package Prefixes
Suppose that you work for a company named ABC that has constructed the following IDL file:

Widgets.idl
module Widgets
{
interface W1 {...};
interface W2 {...};
};

Running this file through the IDL-to-Java compiler will place the Java bindings for W1 and W2 within the package Widgets. But there is an industry convention that states that a company's packages should reside within a package named com.<company name>. The Widgets package is not good enough. To follow convention, it should be com.abc.Widgets. To place this package prefix onto the Widgets module, execute the following:
idlj -pkgPrefix Widgets com.abc Widgets.idl
If you have an IDL file which includes Widgets.idl, the -pkgPrefix flag must appear in that command also. If it does not, then your IDL file will be looking for a Widgets package rather than a com.abc.Widgets package.
If you have a number of these packages that require prefixes, it might be easier to place them into the idl.config file described above. Each package prefix line should be of the form:
PkgPrefix.<type>=<prefix>
So the line for the above example would be:
PkgPrefix.Widgets=com.abc

Defining Symbols Before Compilation
You may need to define a symbol for compilation that is not defined within the IDL file, perhaps to include debugging code in the bindings. The command
idlj -d MYDEF My.idl
is the equivalent of putting the line #define MYDEF inside My.idl.
Preserving Pre-Existing Bindings
If the Java binding files already exist, the -keep flag will keep the compiler from overwriting them. The default is to generate all files without considering if they already exist. If you've customized those files (which you should not do unless you are very comfortable with their contents), then the -keep option is very useful. The command
idlj -keep My.idl
emit all client-side bindings that do not already exist.
Viewing Progres of Compilation
The Idl-to-Java compiler will generate status messages as it progresses through its phases of execution. Use the -v option to activate this "verbose" mode:
idlj -v My.idl
By default the compiler does not operate in verbose mode.
Displaying Version Information

To display the build version of the IDL-to-Java compiler, specify the -version option on the command-line:
idlj -version
Version information also appears within the bindings generated by the compiler. Any additional options appearing on the command-line are ignored.

Options

-d symbol

This is equivalent to the following line in an IDL file:
#define symbol
-emitAll

Emit all types, including those found in #include files.

-fside

Defines what bindings to emit. side is one of client, server, serverTIE, all, or allTIE. Assumes -fclient if the flag is not specified.

-i include-path

By default, the current directory is scanned for included files. This option adds another directory.

-keep

If a file to be generated already exists, do not overwrite it. By default it is overwritten.

-pkgPrefix type prefix

Wherever type is encountered at file scope, prefix the computed Java package name with prefix for all files generated for that type. type is the simple name of either a top-level module, or an IDL type defined outside of any module.

-td dir

Use dir for the output directory instead of the current directory.

-nowarn, -verbose

Verbose mode.

-version

Display version information and terminate.

-Joption
Pass option to the Java virtual machine, where option is one of the options described on the reference page for the java application launcher. For example, -J-Xms48m sets the startup memory to 48 megabytes.
See the Description section for more option information.

Restrictions:

Escaped identifiers in the global scope may not have the same spelling as IDL primitive types, Object, or ValueBase. This is because the symbol table is pre-loaded with these identifiers; allowing them to be redefined would overwrite their original definitions. (Possible permanent restriction).

No local stubs, and no copy semantics when passing values locally (awaiting POA implementation).

The fixed IDL type is not supported.

The generated stubs do not support Serialization, due to IDL/Java mapping specification 1998-08-22 section 25.3.1.3 failing to specify what's required.

Constants of type octet cannot be declared.

Known Problems:

The Java bindings for IDL valuetypes produced by the IDL compiler are not fully compliant with the latest OMG revision of the Objects By Value specification. Fully compliant bindings will be supported in a future release of the compiler.

In some cases, the Java class generated by the compiler from an IDL valuetype definition may not contain a no-argument constructor. If this occurs, edit the generated code to add an empty public or protected no-argument constructor.

The compiler may complete the compilation process without errors but fail to generate output. If this happens, specify the -emitAll option.

The compiler does not recognize the deprecated CORBA::Principal type.

Declaration of a constant and method or attribute having the same name in the same scope does not cause an error. The following IDL should cause an error but doesn't:

      interface t {
        const long foo = 1;
        attribute long foo;
      };

The following IDL results in an error for "S is an undeclared type" in interface B. It shouldn't.

      interface A { struct S { short s; }; };
      interface B:A { typedef S new_S;
                      exception ex {S f1;}; // Error for "S" here
      };

If a union defines another union in its default clause, the resulting Java class gets compilation errors. The work-around is to define the nested union outside of the containing union.