Examples of methods for dynamically loading dll files in JavaWeb projects
这篇文章主要介绍了JavaWeb项目中dll文件动态加载方法,步骤详细,在这里分享给大家,需要的朋友可以了解下。
相信很多做Java的朋友都有过用Java调用JNI实现调用C或C++方法的经历,那么Java Web中又如何实现DLL/SO文件的动态加载方法呢。今天就给大家带来一篇JAVA Web项目中DLL/SO文件动态加载方法的文章。
在Java Web项目中,我们经常会用到通过JNI调用dll动态库文件来实现一些JAVA不能实现的功能,或者是一些第三方dll插件。通常的做法是将这些dll文件复制到 %JAVA_HOME%\jre\bin\ 文件夹或者 应用中间件(Tomcat|Weblogic)的bin目录下之后,在程序中才能正常使用。但是这个步骤在项目实施或移植时经常会被忘记,比较麻烦,所以就考虑能否在项目运行过程中动态加载,而不需要再手动复制这些文件。在网上找了很多资料,大部分的说法要么是手动复制,要么就是JAVA项目中的解决方法(不适用于JAVA Web项目),所以整理此资料,以供参考。
第一步 建立一个监听类
建立监听类的作用是在应用中间件启动时自动执行加载程序。
1)创建一个类实现ServletContextListener 接口
2)实现contextInitialized方法
3)在项目的web.xml 文件中配置此监听类
第二步 将dll文件所在的路径添加到系统环境java.library.path 中
添加过程需要使用到反射机制来进行,不能使用System.setProperty()进行设置,设置了也无效。直接看代码:
private void addDirToPath(String s){ try { //获取系统path变量对象 Field field=ClassLoader.class.getDeclaredField("sys_paths"); //设置此变量对象可访问 field.setAccessible(true); //获取此变量对象的值 String[] path=(String[])field.get(null); //创建字符串数组,在原来的数组长度上增加一个,用于存放增加的目录 String[] tem=new String[path.length+1]; //将原来的path变量复制到tem中 System.arraycopy(path,0,tem,0,path.length); //将增加的目录存入新的变量数组中 tem[path.length]=s; //将增加目录后的数组赋给path变量对象 field.set(null,tem); } catch (Exception e) { e.printStackTrace(); } }
第三步 加载dll文件
接下来就可以写上下文初始化的方法了:
public void contextInitialized(ServletContextEvent arg0) { //获取存放dll文件的绝对路径(假设将dll文件放在系统根目录下的WEB-INF文件夹中) String path=arg0.getServletContext().getRealPath("WEB-INF"); //将此目录添加到系统环境变量中 addDirToPath(path); //加载相应的dll文件,注意要将'\'替换为'/' System.load(path.replaceAll("\\\\","/")+"/XXXX.dll"); }
第四步 重启启动应用中间件(Tomcat|Weblogic)
至此就可以在你的java程序中使用dll文件的方法了。
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