使用java.library.path和LD_LIBRARY_PATH的区别

Question

-Djava.library.path=/path 

export LD_LIBRARY_PATH=/path 

Answer 1

第一种形式

-Djava.library.path=/path

将在java字节码级别处理，system.loadLibrary将调用runtime.loadlibary，然后调用java/lang/classloader.loadLibrary。在函数callclassloader.loadLibrary中，将检查系统属性java.library.path以获取库的完整路径，并将此完整路径传递给本机代码以调用系统apidlopen/dlsym，最终加载库。您可以从OpenJDK存储库中浏览源代码。下面的代码段是我从链接中复制的段。

这种表单的优点是，如果库路径有问题，您将在Java代码中得到错误、警告或异常。

// Invoked in the java.lang.Runtime class to implement load and loadLibrary.
static void loadLibrary(Class fromClass, String name,
                        boolean isAbsolute) {
    ClassLoader loader =
        (fromClass == null) ? null : fromClass.getClassLoader();
    if (sys_paths == null) {
        usr_paths = initializePath("java.library.path");
        sys_paths = initializePath("sun.boot.library.path");
    }
    if (isAbsolute) {
        if (loadLibrary0(fromClass, new File(name))) {
            return;
        }
        throw new UnsatisfiedLinkError("Can't load library: " + name);
    }
// ....

export LD_LIBRARY_PATH=/path

 dlopen()
   The function dlopen() loads the dynamic library file named by the null-terminated string filename and returns an opaque  "handle"  for  the
   dynamic  library.   If  filename is NULL, then the returned handle is for the main program.  If filename contains a slash ("/"), then it is
   interpreted as a (relative or absolute) pathname.  Otherwise, the dynamic linker searches for the library as follows (see ld.so(8) for fur‐
   ther details):

   o   (ELF  only)  If  the  executable  file for the calling program contains a DT_RPATH tag, and does not contain a DT_RUNPATH tag, then the
       directories listed in the DT_RPATH tag are searched.

   o   If, at the time that the program was started, the environment variable LD_LIBRARY_PATH was defined to contain a colon-separated list of
       directories, then these are searched.  (As a security measure this variable is ignored for set-user-ID and set-group-ID programs.)