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jni - gcc

使用GCC构建so; loadLibrary()

xbfLibR.dll generated by Delphi, Error in Ubuntu:

java.lang.UnsatisfiedLinkError: /tmp/xbfLibR1872218867548961332.dll: /tmp/xbfLibR1872218867548961332.dll: 
invalid ELF header (Possible cause: endianness mismatch)
  • JNI Header
  • C++

JNI Header

  • Write a Java Class ReadXbf.java that uses C/C++ Codes
package com.cartionsoft.xbf;

public class ReadXbf {
    static {
      System.loadLibrary("XbfLibR1");  // Load native library XbfLibR1.dll (Windows) or libXbfLibR1.so (Unixes)
                                   //  at runtime
                                   // This library contains a native method called sayHello()
    }
    // Declare an instance native method sayHello() which receives no parameter and returns void
    private native String sayHello(int num, String text);

    // Test Driver
    public static void main(String[] args) {
      ReadXbf rf = new ReadXbf();
      String text = rf.sayHello(1, "world"); // Create an instance and invoke the native method
      System.out.println(text);
    }
}
  • Generate the JNI Header File
javac -h . ReadXbf.java

JNI with C++

XbfLibR1.cpp:

#include <string.h>

#include "com_cartionsoft_xbf_ReadXbf.h" // Generated

JNIEXPORT jstring 
JNICALL 
Java_com_cartionsoft_xbf_ReadXbf_sayHello(
        JNIEnv *env, jobject obj, 
        jint num,
        jstring string) {
    jstring result;
    char msg[60];

    const char *name = env->GetStringUTFChars(string, NULL);//Java String to C Style string

    if (num < 5)
        strcpy(msg, "Hello ");
    else
        strcpy(msg, "NiHao ");
    strcat(msg, name);

    env->ReleaseStringUTFChars(string, name);
    result = env->NewStringUTF(msg); // C style string to Java String
    return result;
}

Generate .so

  • linux
g++ -shared -fPIC -I"$JAVA_HOME/include" -I"$JAVA_HOME/include/linux" XbfLibR1.cpp -o libXbfLibR1.so

!!!Note!!!: System.loadLibrary() is the file name that requires a fixed format

By example, libXXXX.so for linux family, your XbfLibR1.so should rename to libXbfLibR1.so

launch

  • exec
java com.cartionsoft.xbf.ReadXbf
  • temporary exec
java -Djava.library.path=. com.cartionsoft.xbf.ReadXbf

java library

vi ~/.bashrc

add lib path:

export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/home/xb

Effective immediately:

source ~/.bashrc
  • see library
java -XshowSettings:properties

info:

 java.library.path =
        /home/xb
        /usr/java/packages/lib/amd64
        /usr/lib/x86_64-linux-gnu/jni
        /lib/x86_64-linux-gnu
        /usr/lib/x86_64-linux-gnu
        /usr/lib/jni
        /lib
        /usr/lib

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