fixed Issue #263

src/main/javassist/util/proxy/ProxyFactory.java

 import javassist.bytecode.FieldInfo;
 import javassist.bytecode.MethodInfo;
 import javassist.bytecode.Opcode;
+import javassist.bytecode.SignatureAttribute;
 import javassist.bytecode.StackMapTable;
 
 /*
     private String basename;
     private String superName;
     private Class<?> thisClass;
+    private String genericSignature;
+
     /**
      * per factory setting initialised from current setting for useCache but able to be reset before each create call
      */
         signatureMethods = null;
         hasGetHandler = false;
         thisClass = null;
+        genericSignature = null;
         writeDirectory = null;
         factoryUseCache = useCache;
         factoryWriteReplace = useWriteReplace;
         signature = null;
     }
 
+    /**
+     * Sets the generic signature for the proxy class.
+     * <p>For example,
+     *
+     * <pre>class NullPtr&lt;T&gt; {
+     *     T get() { return null; }
+     * }
+     * </pre>
+     *
+     * <p>The following code makes a proxy for <code>NullPtr&lt;String&gt;</code>:
+     *
+     * <pre>ProxyFactory factory = new ProxyFactory();
+     * factory.setSuperclass(NullPtr.class);
+     * factory.setGenericSignature("LNullPtr&lt;Ljava/lang/String;&gt;;");
+     * NullPtr&lt;?&gt; np = (NullPtr&lt;?&gt;)factory.create(null, null);
+     *java.lang.reflect.Type[] x = ((java.lang.reflect.ParameterizedType)np.getClass().getGenericSuperclass())
+     *                                                                     .getActualTypeArguments();
+     * // x[0] == String.class
+     * </pre>
+     * 
+     * @param sig   a generic signature.
+     * @see javassist.CtClass#setGenericSignature(String)
+     * @since 3.26
+     */
+    public void setGenericSignature(String sig) {
+        genericSignature = sig;
+    }
+
     /**
      * Generates a proxy class using the current filter.
      * The module or package where a proxy class is created
         finfo4.setAccessFlags(AccessFlag.PUBLIC | AccessFlag.STATIC| AccessFlag.FINAL);
         cf.addField(finfo4);
 
+        if (genericSignature != null) {
+            SignatureAttribute sa = new SignatureAttribute(pool, genericSignature);
+            cf.addAttribute(sa);
+        }
+
         // HashMap allMethods = getMethods(superClass, interfaces);
         // int size = allMethods.size();
         makeConstructors(classname, cf, pool, classname);

src/test/Test.java

 
         final CtClass ctClass = classPool.get(INVALID_STACK_MAP_FRAME);
         final CtMethod method = ctClass.getDeclaredMethod("bytecodeVerifyError");
-        method.addLocalVariable("test_localVariable", CtClass.intType);
-        method.insertBefore("{ test_localVariable = 1; }");
-        ctClass.debugWriteFile();
+        // method.addLocalVariable("test_localVariable", CtClass.intType);
+        method.insertBefore("{ java.math.BigDecimal d = null; d.divide(d); }");
+        //ctClass.debugWriteFile();
+        System.out.println("ok");
+        ctClass.writeFile();
         Class<?> cc = ctClass.toClass();
         System.out.println(cc.getName());
         InvalidStackMapFrame obj = (InvalidStackMapFrame)cc.getDeclaredConstructor().newInstance();

src/test/javassist/proxyfactory/GenSig.java

+package javassist.proxyfactory;
+
+class GenSig<T> {
+}

src/test/javassist/proxyfactory/ProxyFactoryTest.java

             }
         });
     }
+
+    // Issue #263
+    public void testGenericSignature() throws Exception {
+        ProxyFactory factory = new ProxyFactory();
+        factory.setSuperclass(GenSig.class);
+        factory.setGenericSignature("Ljavassist/proxyfactory/GenSig<Ljava/lang/Integer;>;");
+        GenSig gs = (GenSig)factory.create(null, null);
+        java.lang.reflect.Type[] x = ((java.lang.reflect.ParameterizedType)gs.getClass().getGenericSuperclass())
+                                                                             .getActualTypeArguments();
+        assertEquals(Integer.class, x[0]);
+    }
 }