java - Javassist: creating an interface that extends another interface with generics -

i using javassist in project , need create following interface @ runtime:

package com.example;  import org.springframework.data.repository.crudrepository; import com.example.cat;  public interface catrepository extends crudrepository<cat, long> {} 

while had no problem creating interface catrepository extending crudrepository, not understand (from docs , looking @ source code), how specify com.example.cat , java.lang.long generics types super-interface.

please note that:

• com.example.cat: created @ runtime using javassist (no problems that, have tested , works
• org.springframework.data.repository.crudrepository: existent class library.

if 1 great!

thanks! luca

short answer

the generic information can manipulated in javassist using signatureattribute.

long answer (with code)

the code have this:

 classpool defaultclasspool = classpool.getdefault();  ctclass superinterface = defaultclasspool.getctclass(crudrepository.class             .getname());  ctclass catrepositoryinterface = defaultclasspool.makeinterface("catrepository", ctclass);  // missing here :-(   catrepositoryinterface.toclass() 

but, said not add information generics. in order achieve same bytecode compiling source code, need following comment is:

signatureattribute signatureattribute = new signatureattribute(             classfile.getconstpool(),      "ljava/lang/object;lorg/springframework/data/repository/crudrepository<lorg/example/cat;ljava/lang/long;>;"); classfile metainformation = catrepositoryinterface.getclassfile(); classfile.addattribute(signatureattribute); 

let's break down signature string in order understand what's happening there:

• you see several l[type], it? l standard notation in bytecode define object class, can read more if you're interested in jvm specification regarding descriptors

• ';' being used separator between several definitions. let's @ each 1 of them:

  • ljava/lang/object
  • lorg/springframework/data/repository/crudrepository<lorg/example/cat;ljava/lang/long;>

the first definition has there because in java language extends java.lang.object (doesn't matter if class or interface).

but interesting 1 second one, there have type full classname , generic types definitions, using l notation. that's missing :-)

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note

keep in mind if want extend more 1 interface, have add them in list example, following signature make interface not extend crudrepository serializable:

ljava/lang/object;lorg/springframework/data/repository/crudrepository<lorg/example/cat;ljava/lang/long;>;**ljava/io/serializable;**