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Exceptions in JNI in Java Render PDF 417 in Java Exceptions in JNI

22.10 Exceptions in JNI use tomcat pdf-417 2d barcode creation toinsert pdf417 with java .NET Framework 3.5 If you want only to check servlet barcode pdf417 on the existence of a pending exception without creating a local reference to the jthrowable exception object, the ExceptionCheck() function may be used. It returns JNI-TRUE if an exception is pending and JNI-FALSE if not. Often, after detecting an exception in native code, what you really want to do is handle the exception in Java code by throwing your own exception, perhaps with a bit more description about what went wrong.

Or sometimes, by careful coding, you might detect an error condition in your own native code even before calling a JNI function that would raise an exception. In these cases, you need to throw your own exceptions back to Java, the subject of the next section..

22.10.2 Throwing exceptions in native code Suppose we determine, eith pdf417 2d barcode for Java er by detecting an exception thrown by a JNI function we called, or by our own error checking of the arguments received from the Java side, that some of the arguments are invalid. In that case we might want to throw a java.lang.

IllegalArgumentException back to the Java code. On the Java side, throwing an IllegalArgumentException is simple:. throw new IllegalArgumentE xception ("...

");. Throwing an exception on t spring framework pdf417 2d barcode he native side is only slightly more complicated. The ThrowNew() function is used to throw an exception from native code to Java. This function takes a jclass specifying the exception class to be thrown and a string message to include with the exception.

Therefore we must rst nd the jclass representing the IllegalArgumentException. We can nd that jclass using FindClass(), just like nding any other class:. jclass iae-cls = jenv-> FindClass ("java/lang/IllegalArgumentException"); if (iae-cls == NULL) // just give up if we can t even find the // IllegalArgumentException class return;. With the desired exception PDF417 for Java jclass in hand, we throw it as follows:. jenv->ThrowNew (iae-cls , "illegal argument detected in native code");. The second parameter to Th PDF417 for Java rowNew() is the message to be used when constructing the java.lang.Exception or java.

lang.Throwable object. On the Java side, J2SE 1.

4 added the ability to chain exceptions by specifying a Throwable as a cause parameter to the Exception and Throwable constructors. As of this writing, there is no simple way to provide a Throwable cause. The Java Native Interface (JNI). from native code. (The not spring framework PDF417 -so-simple way is to explicitly construct a Throwable object and provide it a cause. Then use the JNI Throw() function.

) For special needs, you can de ne custom Exception classes in Java that extend java.lang.Exception.

If a custom exception can be found in the CLASSPATH, then FindClass() can nd it and native code can throw the custom exception just as well as the standard Java library exceptions.. 22.11 Local and global references The JVM must keep track of j2ee barcode pdf417 references to all Java objects passed to native code, primarily so the Java garbage collector does not arbitrarily free an object while it is in use in the native code. There are two basic types of references to objects used by native code: local and global references. Local references are valid only during the duration of the native method call.

They are freed automatically upon return from native code to Java. Global references exist even after the native method goes out of scope. Global references must be freed explicitly by the programmer when no longer needed.

All objects are passed to native code as local references, and all objects created within the native code by JNI functions such as NewStringUTF() are created as local references. This arrangement is normal and expected. When the native method returns, the local references are deleted, permitting the garbage collector to free the memory associated with those objects if needed (and, of course, if there are no outstanding references still in use on the Java side).

For special needs, JNI permits you to create global references from local references with the NewGlobalRef() function. If a global reference is created, then it is vital that DeleteGlobalRef() be called when the global reference is no longer needed. Otherwise, a memory leak and/or heap fragmentation can occur as the Java garbage collector is never able to free or move the memory associated with the global reference.

A tempting but mistaken tactic is to attempt to cache a jclass across native method invocations in order to save the cost of the call to GetObjectClass() or FindClass(). Under normal circumstances, the jclass is a local reference and so it becomes no longer valid after the rst native method returns. An attempt to use the cached value on a subsequent call to the native method produces unpredicatable results, possibly including a JVM crash.

A related mistake is to attempt to cache method or eld IDs, probably in an attempt to save the cost of calling GetMethodID() or GetFieldID(). It turns out that method and eld IDs are valid only as long as the class from which the ID is derived is not unloaded. After a native method returns to Java code, the Java garbage collector could possibly unload the class to which the IDs refer.

If so, then subsequent use of the cached IDs can result in unpredictable behavior. To solve the latter problem it is safest to re-compute the eld or method IDs when needed again. Another solution is to create a global reference to the jclass that remains valid even after the native method goes out of scope.

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