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ESSENTIAL JNI JAVA NATIVE INTERFACE PDF

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The Java™ Native. Interface. Programmer's Guide and Specification myavr.info Page 1 Thursday, property rights that are essential to practice this specification. Java Native Interface (JNI) is the Java interface to non-Java code. ▻ interoperate .. “STL was designed with four fundamental ideas in mind: ▻ Abstractness. Java Native Interface. JNI is a mechanism that allows. • a Java program to call a function in a C or C++ program. • a C or C++ program to call a method in a Java.


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Java Native Interface. CSx Lecture. Department of Computer Science. Iowa State University. Introduction. What is native method and JNI. Why we use JNI. The Java Native Interface (JNI) is a native programming interface that is part of the other tools essential for the completion of this tutorial. called the Java Native Interface (JNI). Microsoft uses a their own API in their Java interpreter. Native then creating an instance wouldn't be necessary.

The Java run-time environment is specifically designed to limit the harm that a Java application can cause to the system that it is running on. This is especially important with the World Wide Web, where Java applets are downloaded and executed automatically when a user visits a Web page that contains Java applets.

Using the Java Native Interface (JNI) to defeat Java decompilation

Normally one would not want to execute random programs; they might contain viruses, or they might even be potentially malicious themselves and not merely carrying unwelcome code unintentionally. Unless the user specifically allows it by setting the appropriate flags in the user-interface to the JVM , a Java applet cannot read or write to attached storage devices except perhaps to a specific, restricted area , nor can it read or write to memory locations except to a specific, restricted area.

Not only are Java applets designed for downloading over the network, standard Java libraries also specifically support client-server computing. The Java language includes provisions for multi-threading and for network communications.

Compared to other languages such as C , it is much easier to write a pair of programs, one executing locally on the user's computer that is handling the user-interaction, and the other executing remotely on a server, which is performing potentially more sophisticated and processor-intensive work.

While the Java language is designed to be platform-independent and to execute primarily in a secure environment, programmers can extend Java applications through the use of compiled native binary code on the host operating system using C-style calling conventions through the Java Native Interface JNI.

Because of this, Java programs can accomplish tasks that are not normally allowed via the JVM at the cost of being platform-specific. However, with a well-designed architecture, a Java language programmer can cleanly isolate the platform-independent portion, and present a clean, platform-independent object API to other Java components while at the same time accomplishing platform-specific tasks.

However, since JNI exposes a very platform independent and opaque representation of the JVM, its data and services, overheads exist.

Although the pointer is essential to JNI's platform independence, the pointer may also be costly because additional branches and table lookups are performed during a JNI function call.

For example, to access string and array parameters passed from Java to native code, special invocations of JNI functions are required.

These special invocations cause expensive runtime copy operations to avoid touching the JVM's copy of the data.

However, these functions are implemented at the JVM's discretion and the use of these functions places certain restrictions on the programmer's freedom.

For field and method access, JNI function calls are also required to modify objects and access JVM services from the native code. For example, to modify an object's field or call a class's method, a handle to the appropriate data must first be retrieved. This retrieval is typically implemented as a traversal on the JVM's reflective data structures, in addition to expensive string-based signature comparison operations at runtime. This traversal is orders of magnitude slower than direct field accesses in Java.

These JNI functions include functions that instantiate objects, manage references, handle exceptions, support synchronization and reflection, and ones that are in the Java invocation API for embedding JVMs inside native code. Several attempts have been made to minimize the overhead of JNI function calls.

The first of these attempts are programmer-based optimizations in the form of efficient coding techniques when writing native code that uses the JNI API. The JNI specification also provides a set of critical functions that may return direct references to JVM data and objects and suggests ways to avoid calling into JNI API, for example, caching field and method IDs during static initialization of classes. Another attempt involves removing native function related overheads by minimizing dependencies on JNI API functions by restricting the type of functionality that can be offered in native code.

However, this mechanism may only be used for methods that are guaranteed not to require garbage collection, exception handling, synchronization or any type of security support since these are the types of functionality the wrappers provide.

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In yet another attempt to minimize the overhead of JNI function calls, compilers may use proprietary native interfaces that are tightly coupled to the VM, since the interfaces have knowledge of the internals of the VM. An example of such compilers is the Jcc compiler, which is an optimizing compiler that compiles directly to native code using a proprietary native interface reminiscent of the original Native Method Interface NMI , from Sun Microsystems, Inc.

In this way, Jcc may inline short assembly segment to speed up native calls. While the above attempts minimizes some of the overhead associated with JNI function calls, there is no existing mechanism that does not restrict the type of functionality implemented in native code, as mentioned in the second attempt, or does not couple to a specific VM implementation, as mentioned in the third attempt. Therefore, it would be advantageous to have a method, an apparatus, and computer instructions for use by a Just in Time JIT compiler transforming JNI function calls to constants, internal compiler operations or a simpler intermediate representation, such that performance of native codes accessing JVM data and services may be improved without coupling to a specific VM implementation or sacrificing type safety of the JNI.

After compiling a program to generate a list of shapes for a plurality of Java Native Interface JNI function calls, an inliner is provided to identify a list of native interface function or JNI calls made in native code for transformation. Subsequently, a JIT call transformer is provided to transform a portion of the list of native interface function calls into constants, internal just-in-time compiler operations or simpler intermediate representation using results of the definition and use analysis.

During inlining of native functions calls, the just-in-time inliner determines, for each native interface call occurring in the inlined code, if the native interface environment variable used in the call is in the same position as it appears in a list of pre-defined shapes representing all known native interface calls.

The shape of a JNI call includes 1 the means represented in the intermediate representation to access the actual target native interface or JNI function 2 the treatment again in the intermediate representation each actual argument receives. The shape of a representative JNI call as created when building the list of shapes uniquely determines the actual JNI routine. If the native interface environment variable used in a call is in the same position as in one of the shapes in the list of pre-defined shapes representing native interface calls, the inliner determines if a match exists between the shape and the intermediate representation of the JNI call made by an inlined native function.

If a match exists between the shape and the intermediate representation of the JNI function call, the inliner adds the JNI call to a list of JNI function calls for the currently inlined native method, wherein the list of calls is sorted in an order of appearance in the intermediate representation of the plurality of JNI calls.

After performing definition and use analysis, the just-in-time call transformer determines, for each native interface function call in the list of native interface function calls, the type of the native interface function calls, and attempts to replace each native interface function call with a constant value, internal just-in-time compiler operation or a simpler intermediate representation depending on the type of JNI function call.

Since the newly generated constants, internal just-in-time compiler operations or simpler intermediate representation perform without using the JNI, they in turn provide direct and faster access to the services and data of the Java virtual machine.

The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: FIG. A computer is depicted which includes system unit , video display terminal , keyboard , storage devices , which may include floppy drives and other types of permanent and removable storage media, and mouse Additional input devices may be included with personal computer , such as, for example, a joystick, touchpad, touch screen, trackball, microphone, and the like.

Although the depicted representation shows a computer, other embodiments of the present invention may be implemented in other types of data processing systems, such as a network computer.

Computer also preferably includes a graphical user interface GUI that may be implemented by means of systems software residing in computer readable media in operation within computer With reference now to FIG.

Data processing system is an example of a computer, such as computer in FIG. Data processing system employs a peripheral component interconnect PCI local bus architecture. PCI bridge also may include an integrated memory controller and cache memory for processor Additional connections to PCI local bus may be made through direct component interconnection or through add-in connectors.

In the depicted example, local area network LAN adapter , small computer system interface SCSI host bus adapter , and expansion bus interface are connected to PCI local bus by direct component connection. Expansion bus interface provides a connection for a keyboard and mouse adapter , modem , and additional memory An operating system runs on processor and is used to coordinate and provide control of various components within data processing system in FIG.

The operating system may be a commercially available operating system such as Windows XP, which is available from Microsoft Corporation. An object oriented programming system such as Java may run in conjunction with the operating system and provides calls to the operating system from Java programs or applications executing on the data processing system Instructions for the operating system, the object-oriented programming system, and applications or programs are located on storage devices, such as hard disk drive , and may be loaded into main memory for execution by processor Those of ordinary skill in the art will appreciate that the hardware in FIG.

Other internal hardware or peripheral devices, such as flash read-only memory ROM , equivalent nonvolatile memory, or optical disk drives and the like, may be used in addition to or in place of the hardware depicted in FIG.

Also, the processes of the present invention may be applied to a multiprocessor data processing system.

For example, data processing system , if optionally configured as a network computer, may not include SCSI host bus adapter , hard disk drive , tape drive , and CD-ROM In that case, the computer, to be properly called a client computer, includes some type of network communication interface, such as LAN adapter , modem , or the like. As another example, data processing system may be a stand-alone system configured to be bootable without relying on some type of network communication interface, whether or not data processing system comprises some type of network communication interface.

The depicted example in FIG.

For example, data processing system also may be a notebook computer or hand held computer in addition to taking the form of a PDA. Data processing system also may be a kiosk or a Web appliance. The processes of the present invention are performed by processor using computer implemented instructions, which may be located in a memory such as, for example, main memory , memory , or in one or more peripheral devices Java-based system contains platform specific operating system that provides hardware and system support to software executing on a specific hardware platform.

JVM is one software application that may execute in conjunction with the operating system. JVM provides a Java run-time environment with the ability to execute a Java application or applet , which is a program, servlet, or software component written in the Java programming language.

The computer system in which JVM operates may be similar to data processing system or computer described above. However, JVM may be implemented in dedicated hardware on a so-called Java chip, Java-on-silicon, or Java processor with an embedded picoJava core.

At the center of a Java run-time environment is the JVM, which supports all aspects of Java's environment, including its architecture, security features, mobility across networks, and platform independence. Note: MRJ 2. This problem has been fixed in MRJ 2. The library file needs to be on the CFM search path. Basically, this means that it needs to be: Inside the application itself In the same folder as the application In the Extensions folder In a folder directly contained in the Extensions folder, e.

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This is not recursive -- sub-folders of MRJ Libraries will not be searched. A common mistake is to put the library in the MRJClasses folder. Note that if you're running your code directly from JBindery without saving the settings as an app, then "the application" means JBindery itself. If your native code is being used by a specific application, then the usual place to put the library is into the same folder as the app.

Embedding the code fragment within the application itself is tempting, especially since -- if combined with a Virtual File System -- you can boil your whole app down to a single file. Since the data fork is already in use by the VFS, the best place to put the code fragment is into a resource.

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You'll have to tell the linker to generate a code resource, then copy the resource into the app and add a new entry to the app's 'cfrg' resource to point to your code fragment. Back to top Debugging The Loading Process If you have a pesky native library that just flat-out refuses to load even after you've used all the previous information to troubleshoot it, here's a way to debug some of the loading process.

You must have MacsBug installed to do this. Before your app tries to load the native library, break into MacsBug by holding down the Command cloverleaf key and pressing the Power key.

Enter the command: tvb GetSharedLibrary ';dm r3 pstring' then enter "g" to continue. At the next point where MRJ tries to load a native library, you will hit the breakpoint and drop into MacsBug.

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MRJ loads a lot of libraries when it starts up, so this may not be the library you're looking for. If not, enter "g" to continue and go back to step 3. This is a very simple approach but incredibly expressive. Our design will pass keyword-value pairs as the argument for the native execute method. The return values will also be a series of keyword-value pairs. Our native method then is a method that takes a string and returns a string. Therefore, instead of trying to capture the string manipulation logic in NativeCommand, we will have a base class called NativeMessage.

The first issue is efficiency. By creating a signature that only deals with strings you are forced to spend processing time converting to and from textual representations. Fortunately for us efficiency is not an issue for most GUI designs since most of the time they are being driven at human speeds and the computation time for parsing becomes trivial. The second issue is type safety. By forcing everything into a string we lose valuable type information. This concern can be minimized by hiding most of the string manipulation logic in low-level base classes that are not used directly by anyone.

In the derived classes our data will be strongly typed and the fact that it gets converted to strings before it is used will be transparent. The last issue is runtime errors vs. I have to admit this one bothers me. Derived classes will have to put arguments into commands via keywords and get return values from commands via keywords.

If the keyword is not present, we can throw an exception. We have traded compile time errors for runtime errors by generalizing the signature. This is true of many Java package interfaces.Each argument is represented by a set of possible objects depending on the flow of control from the start of the inlined native method to the invocation of the JNI function.

An example of such compilers is the Jcc compiler, which is an optimizing compiler that compiles directly to native code using a proprietary native interface reminiscent of the original Native Method Interface NMI , from Sun Microsystems, Inc. The native keyword transforms our method into a sort of abstract method: If it is your library, double-check that the spelling of the library name is exactly as you specified it to the IDE or linker.

Security The Spring Security guides. I'll start with a quick introduction to JNA and the software required to run the examples in this article.

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