1. Write a Java file, declare the native method, and load the dynamic link library through the static statement block. The example Prompt.java code is as follows:
class Prompt { private native String getLine(String prompt); public static void main(String args[]) { Prompt p = new Prompt(); String input = p.getLine("Type a line: "); System.out.println("User typed: " + input); } static { System.loadLibrary("Prompt"); }} 2. Call the javac command to generate the Prompt.class file;
javac Prompt.java
3. Call the javah command to generate the Prompt.h header file for reference by C program:
javah -jni Prompt
The automatically generated header file is as follows:
/* DO NOT EDIT THIS FILE - it is machine generated */#include <jni.h>/* Header for class Prompt */#ifndef _Included_Prompt#define _Included_Prompt#ifdef __cplusplusextern "C" {#endif/* * Class: Prompt * Method: getLine * Signature: (Ljava/lang/String;)Ljava/lang/String; */JNIEXPORT jstring JNICALL Java_Prompt_getLine (JNIEnv *, jobject, jstring);#ifdef __cplusplus}#endif#endif 4. Write Prompt.c file to implement specific functions:
#include <jni.h>#include <stdio.h>#include "Prompt.h"JNIEXPORT void JNICALLJava_Prompt_getLine(JNIEnv *env, jobject obj, jstring prompt) { char buf[128]; const jbyte *str; str = (*env)->GetStringUTFChars(env, prompt, NULL); if(str == NULL) { return NULL; } printf("%s", str); (*env)->ReleaseStringUTFChars(env, prompt, str); scanf("%s", buf); return (*env)->NewStringUTF(env, buf);} 5. Compile the dynamic library libPrompt.so;
gcc -shared -fpic -I/usr/lib/jvm/java-6-sun-1.6.0.26/include -I/usr/lib/jvm/java-6-sun-1.6.0.26/include/linux Prompt.c -o libPrompt.so
6. Run.
java Prompt
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