is there an Ant task to check if a symlink is dangling or not?

Question

I have some symlinks in my build system that point to jars which I need to build if the jars don't exist. ie if the symlinks are dangling. Is there an Ant task or workaround to check that?

As to why I can't include a proper Ant dependency to those jars, the reason is that their build process is lengthy, involving on-the-fly Internet downloads from ftp repositories that take too long and is out of my control.

Answer 1

Ok, so in the end I implemented a custom Ant task (code at the end), that can be used from Ant like this:

<file-pronouncer filePath="path/to/file" retProperty="prop-holding-type-of-that-file"/>

It can then be read with:

<echo message="the file-pronouncer task for file 'path/to/file' returned: ${prop-holding-type-of-that-file}"/>

With the following possible outcomes:

 [echo] the file-pronouncer task for file 'a' returned: regular-file
 [echo] the file-pronouncer task for file 'b' returned: symlink-ok
 [echo] the file-pronouncer task for file 'c' returned: symlink-dangling
 [echo] the file-pronouncer task for file 'd' returned: not-exists

code for the FilePronouncer custom Ant task

import java.io.IOException;
import org.apache.tools.ant.Project;
import org.apache.tools.ant.Task;
import java.nio.file.Path;
import java.nio.file.Files;
import java.nio.file.FileSystems;
import java.nio.file.LinkOption;
import java.nio.file.attribute.BasicFileAttributes;
import org.apache.tools.ant.BuildException;

public class FilePronouncer extends Task {

    private String filePath    = null;
    private String retProperty = null;

    public String getFilePath() {  
        return filePath;  
    }  

    public void setFilePath(String filePath) {  
        this.filePath = filePath;
    }

    public String getRetProperty() {  
        return retProperty;  
    }  

    public void setRetProperty(String property) {  
        this.retProperty = property;  
    }

    public void execute() {
        try {
        Path path = FileSystems.getDefault().getPath(filePath);
        boolean fileExists           = Files.exists(path, LinkOption.NOFOLLOW_LINKS);
        Boolean isSymlink            = null;
        Boolean filePointedToExists  = null;
        if (fileExists) {
            BasicFileAttributes attrs = Files.readAttributes(path, BasicFileAttributes.class, LinkOption.NOFOLLOW_LINKS);
            isSymlink = attrs.isSymbolicLink();
            if (isSymlink)
                filePointedToExists = Files.exists(path);
        }
        Project project = getProject();  
        String rv = null;
        if (!fileExists)
            rv = "not-exists";
        else {
            if (!isSymlink)
                rv = "regular-file";
            else {
                if (filePointedToExists)
                    rv = "symlink-ok";
                else
                    rv = "symlink-dangling";
            }
        }
        project.setProperty(retProperty, rv);
        } catch (IOException e) {
            throw new BuildException(e);
        }
    }
}