从Java调用C函数库

实验环境：CentOS 6.7

1. 安装JDK
参考：

2. 编写C函数库

/* File : example.c */

double  My_variable = 3.0;

/* Compute factorial of n */
int fact(int n) {
  if (n <= 1) return 1;
  else return n*fact(n-1);
}

/* Compute n mod m */
int my_mod(int n, int m) {
  return(n % m);
}

3. 编写SWIG接口文件

/* File : example.i */
%module example
%{
  /* Put headers and other declarations here */
  extern double My_variable;
  extern int fact(int);
  extern int my_mod(int n, int m);
  %}

extern double My_variable;
extern int fact(int);
extern int my_mod(int n, int m);

4. 生成包装文件，并构建C函数库和包装文件，生成共享库

root [ ~/example ]# swig -java example.i
root [ ~/example ]# gcc -fPIC -c example_wrap.c -I/usr/java/jdk1.8.0_60/include -I/usr/java/jdk1.8.0_60/include/linux
root [ ~/example ]# gcc -fPIC -c example.c
root [ ~/example ]# ld -G example_wrap.o example.o -o libexample.so

5. 编写Java程序调用C函数库

// runme.java

public class runme {
  static {
    System.loadLibrary("example");
  }

  public static void main(String argv[]) {
    System.out.println("fact(4) = " + example.fact(4));
    System.out.println("my_mod(7, 2) = " + example.my_mod(7, 2));
  }
}

6. 编译所有Java源文件并运行

root [ ~/example ]# javac *.java
root [ ~/example ]# java runme
fact(4) = 24
my_mod(7, 2) = 1