无法从 src/main/resources Java 项目 Maven 获取文件夹

Question

I try to loop over all files in a certain folder in my resources (I added this folder myself in eclipse by doing new->folder). Whatever I try it keeps giving a null exception on the line where I try to get the folder. As I need to loop over its content getting it as a stream or something won't work. I tried many approaches, but for example these two gave me the error:

File folder = new File(Thread.currentThread().getContextClassLoader().getResource("schematics").getPath());

This wrapped inside a try catch did also not work:

File folder = new File(getClass().getClassLoader().getResource("schematics").toURI());

My file structure (class where I try to access the schematics is HeavenStructureManager's initialiser):

EDIT This project is a minecraft plugin, bundled to a jar by maven and run by the spigotmc minecraft jar. Their api provides a function getResource() but that gives a InputStream. As I would like to dynamically get all files inside a folder that does not work for me. I unpacked my jar file to check where the schematic is, and it looked like this:

Answer 1

Try using an absolute path:

getClass().getClassLoader().getResource("/schematics")

When you use the getResource method, getResource will try to find the resource relative to the class package. Therefore, when you use the path ("schematics"), in reality, you are referring to the file at the location [resources]/com/ericdebouwer/heaven/schematics. By using a leading / getResource treats it as an absolute path.

Answer 2

Below is a code example to iterate through the contents of a jar file, list them and write the contents to a new file.

Current run directory: .

Jar file directory: ./plugins/org.alloytools.alloy.dist.jar

Output directory: ./unzipped

package com.serge;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.jar.JarEntry;
import java.util.jar.JarInputStream;

public class JarFileReader {
    public static void main(String[] args) {

        try {
            File file = new File("plugins/org.alloytools.alloy.dist.jar");
            FileInputStream fileInputStream = new FileInputStream(file);
            JarInputStream jarInputStream = new JarInputStream(fileInputStream);
            FileOutputStream outputStream = null;

            File unzippedDir = new File("unziped");

            while(jarInputStream.getNextEntry() != null) {
                JarEntry entry = jarInputStream.getNextJarEntry();

                // list the contents of the jar file 
                System.out.println(entry.toString());

                // write contents of a file within the jar file to a new file
                if("help/Nav.html".equals(entry.getName())) {
                    new File(unzippedDir + "/" + entry.getName().substring(0, entry.getName().indexOf("/"))).mkdir();
                    File unzippedFile = new File(unzippedDir + "/" + entry.getName());
                    unzippedFile.createNewFile();
                    outputStream = new FileOutputStream(unzippedFile);

                    byte[] bytes = new byte[1024];

                    int length = 0;

                    while((length = jarInputStream.read(bytes)) > 0) {
                        outputStream.write(bytes, 0, length);   
                    }
                }
            }

            outputStream.close();
            jarInputStream.close();
            fileInputStream.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}