Determining & reading external linked files in java

[mwilliam]

Hello,
As my understanding using the “-e” option of the “ln” command from Unix System Services creates a link from a HFS file name to an external MVS data set. As such, this is usually used by Unix System Services as a mechanism of loading executable modules from PDSE data sets.

However, I have noticed that while using ls command shows the external linked MVS resource name, but any attempt to read to this read this link results in occurring a file not find error.

I am wondering, is there a way (in Java) to determine the actual MVS dataset pointed to by such a link and using jZos to read the dataset contents?

[dovetail]

The JZOS toolkit doesn't really have any classes that deal with HFS files. If you use the SDK's java.io classes, I'm not aware of any mechanism for resolving externally linked files. The only option that I can think of, which is not pretty, is to use Runtime.exec() (or JZOS's Exec class) to launch a z/OS Unix shell command that returns that information.

[mwilliam]

Ok, thanks.

I believe I found a different approach, from a little experiment.
I have discovered, some differences on symbolic links and external links in USS.

Using the java class: java.io.File, though both types of links appear as files, symbolic links are resolvable while external links are not. For a symbolic link, either of the following methods from File class: isFile(), isDirectory() would return the value true, depending on how the link is resolved. As such, from the File class, the method: getPath() returns the name of the link itself, while the method: getCanonicalPath() returns the path name referenced in the symbolic link. Though, on the other hand to test for a external link, both methods of File class: isFile() & isDirectory() all return false.

However, I also discovered from z/OS C/C++ runtime library is the function: readlink() returns the name referenced in the external link.
As with the sample C++ code below, I’ve ran a test using the function:

Code: Select all

Using namespace std;
#include <unistd.h>
#include <cstdio>
#include <cstdlib>

  // I used the follow declaration to resolve compile errors
extern “C” {
  int readlink(const char *, char *, size_t);
}

   // supply path name of symbolic/external link 
int main(int argc, char *argv[])
{
   char buf[256];
   int len;

   if (argc < 2) {
     printf(“usage: %s filename\n”,argv[0]);
   }
   
   if ( (len = readlink(argv[1], buf, sizeof(buf))) < 0)
     perror(“readlink() error”);
   else
     printf(“readlink() returned ‘%s’ for ‘%s’\n”, buf, argv[1]);

   return 0;
}

Next, all I have to do is to write a JNI (wrapper) around this function
Once, I receive the name of the MVS file in java, I then have the option to examine/edit it and pass it on to the appropriate java class to open this file.