Add feature director:except for improved director exception handling in Java

Closes #91

2 files changed, 239 insertions, 2 deletions

diff --git a/Lib/java/director.swg b/Lib/java/director.swg
index f32fda350..8c7dca294 100644
--- a/Lib/java/director.swg
+++ b/Lib/java/director.swg
@@ -193,6 +193,242 @@ namespace Swig {
   };
 }
 
-#endif /* __cplusplus */
 
+// Default exception handler for all director methods.
+// Can override this for specific methods
+// This just documents the default.  It is not actually attached as a feature
+// for efficiency reasons (and is defined in java.cxx)  It can be overridden
+// as a feature for specific methods or globally.
+
+//%feature("director:except") %{
+//  jthrowable $error = jenv->ExceptionOccurred();
+//  if ($error) {
+//    jenv->ExceptionClear();
+//    $directorthrowshandlers
+//    throw Swig::DirectorException(jenv, $error);
+//  }
+//%}
+
+// Define some utility methods and classes.  Cannot use fragments since
+// these may be used by %features and in directorthrows typemaps
+
+#include <exception>
+
+// Simple holder for exception messages, allowing access to a c-style string
+namespace Swig {
+  struct JavaString {
+    JavaString(JNIEnv * jenv, jstring jstr):jenv_(jenv), jstr_(jstr), cstr_(0) {
+      if (jenv_ && jstr_) {
+	// Get the null-terminated c-string out, and hold it
+	cstr_ = (const char *) jenv_->GetStringUTFChars(jstr_, NULL);
+      }
+    }
+    ~JavaString() {
+      if (jenv_ && jstr_ && cstr_) {
+	jenv_->ReleaseStringUTFChars(jstr_, cstr_);
+      }
+    }
+    const char *cstr() {
+      return cstr_ ? cstr_ : "";
+    }
+
+  private:
+    JNIEnv * jenv_;
+    jstring jstr_;
+    const char * cstr_;
+
+    // non-copyable
+    JavaString(const JavaString &);
+    JavaString & operator=(const JavaString &);
+  };
+
+  struct JavaExceptionMessage {
+    JavaExceptionMessage(JNIEnv * jenv, jthrowable excp) :
+      jstrholder_(jenv,exceptionMsgJstr(jenv,excp)) {
+    }
+    ~JavaExceptionMessage() {
+    }
+    const char *message() {
+      return jstrholder_.cstr();
+    }
+
+  private:
+    JavaString jstrholder_;
+
+    // non-copyable
+    JavaExceptionMessage(const JavaExceptionMessage &);
+    JavaExceptionMessage & operator=(const JavaExceptionMessage &);
+
+    // Static method to initialize jstrholder_
+    static jstring exceptionMsgJstr(JNIEnv * jenv, jthrowable excp) {
+      jstring jmsg = NULL;
+      if (jenv && excp) {
+	jenv->ExceptionClear(); // Cannot invoke methods with pending exception
+	jclass thrwclz = jenv->GetObjectClass(excp);
+	if (thrwclz) {
+	  // if no getMessage() or other exception, no msg available.
+	  jmethodID getThrowableMsgMethodID =
+	      jenv->GetMethodID(thrwclz, "getMessage", "()Ljava/lang/String;");
+	  if (getThrowableMsgMethodID && !jenv->ExceptionCheck()) {
+	    // if problem accessing exception message string, no msg available.
+	    jmsg = (jstring)
+	      jenv->CallObjectMethod(excp, getThrowableMsgMethodID);
+	  }
+	}
+	if (jmsg == NULL && jenv->ExceptionCheck()) {
+	  jenv->ExceptionClear();
+	}
+      }
+      return jmsg;
+    }
+  };
+
+
+  ////////////////////////////////////
+
+  bool ExceptionMatches(JNIEnv * jenv, jthrowable excp,
+			const char *clzname) {
+    jboolean matches = false;
+
+    if (excp && jenv && clzname) {
+      // Have to clear exceptions for correct behavior.  Code around
+      //   ExceptionMatches should restore pending exception if
+      //   desired - already have throwable.
+      jenv->ExceptionClear();
+
+      jclass clz = jenv->FindClass(clzname);
+      if (clz && ! jenv->ExceptionCheck()) {
+	jclass classclz = jenv->GetObjectClass(clz);
+	jmethodID isInstanceMethodID =
+	    jenv->GetMethodID(classclz, "isInstance", "(Ljava/lang/Object;)Z");
+	if (isInstanceMethodID) {
+	  matches = (jboolean)
+	      jenv->CallBooleanMethod(clz, isInstanceMethodID, excp);
+	}
+      }
+      // This may happen if user typemaps or director:except
+      // features call ExceptionMatches incorrectly, typically with
+      // an invalid clzname argument.  Uncommenting the debug lines
+      // may help to diagnose.
+      // As is, this leaves the underlying case as a pending exception
+      // which may not be that clear (e.g. ClassNotFoundException)
+
+      // if (jenv->ExceptionCheck()) {
+      // JavaExceptionMessage jstrmsg(jenv,jenv->ExceptionOccurred());
+      // std::cerr << "Error: ExceptionMatches: class '" <<
+      //   clzname << "' : " << jstrmsg.message() << std::endl;
+      // }
+    }
+    return matches;
+  }
+
+  // Provide the class name to allow reconstruction of the original exception
+  struct DirectorException : std::exception {
+
+    // Construct a DirectorException from a java throwable
+    DirectorException(JNIEnv* jenv,jthrowable excp) : classname_(0), msg_(0) {
+      jstring jstr_classname = NULL;
+      jmethodID mid_getName = NULL;
+      jclass thrwclz;
+      jclass clzclz;
+
+      if (excp) {
+	// Get the exception class, like Exception
+	thrwclz = jenv->GetObjectClass(excp);
+	if (thrwclz) {
+	  // Get the java.lang.Class class
+	  clzclz = jenv->GetObjectClass(thrwclz);
+	  if (clzclz) {
+	    mid_getName = jenv->GetMethodID(clzclz, "getName", "()Ljava/lang/String;");
+	    if (mid_getName) {
+	      // Get the excp class name
+	      jstr_classname = (jstring)(jenv->CallObjectMethod(thrwclz, mid_getName));
+	    }
+	  }
+	}
+      }
+      // Copy strings, since no guarantee jenv will be active when handled
+      // If classname_ is 0, returned as "UnknownException"
+      if (jstr_classname) {
+	JavaString classname(jenv, jstr_classname);
+	classname_ = copypath(classname.cstr());
+      }
+      JavaExceptionMessage exceptionmsg(jenv, excp);
+      msg_ = copystr(exceptionmsg.message());
+    }
+
+    // Throw as a wrapped Runtime Error explicitly.
+    DirectorException(const char * msg) : classname_(0), msg_(0) {
+      classname_ = copypath("java/lang/RuntimeError");
+      msg_ = copystr(msg);
+    }
+
+    ~DirectorException() throw() {
+      delete[] classname_;
+      delete[] msg_;
+    }
+
+    // If there was problem finding classname, keep track of error
+    //  On raiseJavaException will be mapped to a RuntimeException
+    const char* classname() const throw() {
+      return classname_ ? classname_ : "UnknownException";
+    }
+    const char* what() const throw() {
+      return msg_ ? msg_ : "";
+    }
+
+    // Python director code provides static raise() methods
+    // Omitted here: Seems less good than
+    //   throw DirectorException(jenv, excp)
+    // from which compiler can infer a C++ exception is thrown.
+
+    // Reconstruct and raise the Java Exception that caused the DirectorException
+    void raiseJavaException(JNIEnv* jenv) {
+      if (jenv) {
+	jenv->ExceptionClear();
+
+	jmethodID strCtorID = 0;
 
+	jclass excpclz = jenv->FindClass(classname());
+
+	if (excpclz) {
+	  strCtorID = jenv->GetMethodID(excpclz,"<init>","(Ljava/lang/String;)V");
+	}
+
+	if (strCtorID) {
+	  // If exception has a string constructor, throw an instance
+	  jenv->ThrowNew(excpclz, what());
+	} else {
+	  // Else, throw a runtime
+	  SWIG_JavaThrowException(jenv, SWIG_JavaRuntimeException, what() );
+	}
+      }
+    }
+
+  private:
+    const char * classname_;
+    const char * msg_;
+
+    static const char * copypath(const char * srcmsg) {
+      return copystr(srcmsg, 1);
+    }
+    static const char * copystr(const char * srcmsg, int pathrepl=0) {
+      char * target = 0;
+      if (srcmsg) {
+	int msglen = 1+strlen(srcmsg); //+1 for null terminator
+	target = new char[msglen];
+	strncpy(target, srcmsg, msglen);
+      }
+      // If pathrepl, replace any '.' with '/'
+      if (pathrepl) {
+	for(char *c=target; *c; ++c) {
+	  if ('.' == *c) *c = '/';
+	}
+      }
+      return target;
+    }
+  };
+
+}
+
+#endif /* __cplusplus */
diff --git a/Lib/java/std_string.i b/Lib/java/std_string.i
index f178e6d43..6b9cb90a4 100644
--- a/Lib/java/std_string.i
+++ b/Lib/java/std_string.i
@@ -38,7 +38,8 @@ class string;
 
 %typemap(directorout) string 
 %{ if(!$input) {
-     SWIG_JavaThrowException(jenv, SWIG_JavaNullPointerException, "null string");
+     if (!jenv->ExceptionCheck())
+       SWIG_JavaThrowException(jenv, SWIG_JavaNullPointerException, "null string");
      return $null;
    } 
    const char *$1_pstr = (const char *)jenv->GetStringUTFChars($input, 0);