Convert JarEntry to File

问题

I'm using a library which wants a File() as an argument.

The file I want to pass it is one I want to package with my app, as part of the .jar

Is there any way to convert the JarEntry that I get from within my .jar to a File object I can pass?

If not and I have to copy the resource to disk temporarily, where's the best place to put the temporary file?

Thanks.

回答1:

You cannot get a path to a file within a JARFile, only a stream, so you should extract it to the temporary directory and then pass that extracted file. Here's a function I wrote to do this when I provided a db with a jar previously.

/**
*  This method is responsible for extracting resource files from within the .jar to the temporary directory.
*  @param filePath The filepath relative to the 'Resources/' directory within the .jar from which to extract the file.
*  @return A file object to the extracted file
**/
public File extract(String filePath)
{
    try
    {
        File f = File.createTempFile(filePath, null);
        FileOutputStream resourceOS = new FileOutputStream(f);
        byte[] byteArray = new byte[1024];
        int i;
        InputStream classIS = getClass().getClassLoader().getResourceAsStream("Resources/"+filePath);
//While the input stream has bytes
        while ((i = classIS.read(byteArray)) > 0) 
        {
//Write the bytes to the output stream
            resourceOS.write(byteArray, 0, i);
        }
//Close streams to prevent errors
        classIS.close();
        resourceOS.close();
        return f;
    }
    catch (Exception e)
    {
        System.out.println("An error has occurred while extracting the database. This may mean the program is unable to have any database interaction, please contact the developer.\nError Description:\n"+e.getMessage());
        return null;
    }
}

回答2:

A File represents a real entry in the filesystem; a JarEntry doesn't exist on the file system. The mapping won't be there unless you extract the JAR entry to an actual file.

You can create a temp file using File.createTempFile. More details are available at this SO answer.

来源：https://stackoverflow.com/questions/17902795/convert-jarentry-to-file

标签

java

jar

executable-jar