Resolving The Problem

Symptom: Java program that uses JNI Program on IBM i to call a native function from Service Program fails with java.lang.UnsatisfiedLinkError().

The important link between the JVM and the native method being called is the name of the native method. The name exported by your service program must match the name expected by the JVM; otherwise, one of the call-time (as opposed to load-time) UnsatisfiedLinkError is thrown.

The name that is created by the JVM (the caller side) must match the name that is exported from MYSRVPGM (the callee).

To see the name that Java creates, do the following:

Start a QSH session and type

javah -jni fully.qualified.class.name

where the fully.qualified.class.name is the name of your class (without the '.class' on the end.) This creates a file in the current directory called fully_qualified_class_name.h that includes the "name" that the JVM will be using to get to the native method.

Example

     javah -jni java.lang.String

  ...results in the file java_lang_String.h

Then, java.lang.String specifies a native method, "intern()", and the section of this header file describing it looks similar to the following:

     /*
      * Class:     java_lang_String
      * Method:    intern
      * Signature: ()Ljava/lang/String;
      */
     JNIEXPORT jstring JNICALL Java_java_lang_String_intern
       (JNIEnv *, jobject);

The important part is the part after JNICALL -- the Java_java_lang_String_intern. This is the name a native method library (also known as the service program) designed to handle this native method must export to make the connection.

To see the names exported by MYSRVPGM, on the operating system command line type the following:

DSPSRVPGM SRVPGM(MYSRVPGM) DETAIL(*PROCEXP)

Press the Enter key.