Can't open an existing file in Java

Question

I'm trying to make the Google Drive Java Quickstart work, but I'm stuck with a NullPointerException when trying to use the InputStream.

Google's quickstart code

InputStream in =
            Quickstart.class.getResourceAsStream("client_secret.json");
        GoogleClientSecrets clientSecrets =
            GoogleClientSecrets.load(JSON_FACTORY, new InputStreamReader(in));

According to one SO question, the getResourceAsStream looks for the file in the same directory as the class calling it, so I put my client_secret.json with my class:

|src/main/java
|---quickstart
|------Quickstart.java
|------client_secret.json

I still have the NullPointerException, so I tried to create the InputStream from a File instead of using getResourceAsStream:

java.io.File initialFile = new java.io.File("A:/Documents/client_secret.json");
//   java.io.File initialFile = new java.io.File("client_secret.json");
if (initialFile.canRead()) {
    System.out.println("it works!");
} else {
    System.out.println("that's a fail");
}
System.out.println(initialFile.getAbsolutePath() + " " + initialFile.exists() + " " + initialFile.getAbsoluteFile().exists());
InputStream in = new FileInputStream(initialFile);

which results in:

that's a fail
A:\Documents\client_secret.json false false
Exception in thread "main" java.io.FileNotFoundException: A:\Documents\client_secret.json (Le fichier spécifié est introuvable)
    at java.io.FileInputStream.open(Native Method)
    at java.io.FileInputStream.<init>(FileInputStream.java:138)
    at quickstart.Quickstart.authorize(Quickstart.java:76)
    at quickstart.Quickstart.getDriveService(Quickstart.java:102)
    at quickstart.Quickstart.main(Quickstart.java:111)

I can find the files when I use the path in my explorer.

I've tried different ways to open the file (absolute path, relative path, using "parent" constructor, ...), but always the same result. This code works when I execute it on online java compilers though (like tutorialspoint's one).

My OS is Windows 10, I'm working with Eclipse IDE.

Answer 1

This is explain in the complete answer of LordOfThePigs.

In Class.getResourceAsStream(path), the path is interpreted as a path local to the package of the class you are calling it from. For example calling, String.getResourceAsStream("myfile.txt") will look for a file in your classpath at the following location: "java/lang/myfile.txt". If your path starts with a /, then it will be considered an absolute path, and will start searching from the root of the classpath. So calling String.getResourceAsStream("/myfile.txt") will look at the following location in your class path ./myfile.txt.

Your path is defined like an absolute one, absolute to the root of the classpath.

Quickstart.class.getResourceAsStream("client_secret.json"); // remove the "/"

---

Example

- src
    - labo
        - Main.java
        - Test.log // > Hello from Labo
    - Test.log // > Hello from Source Package

This will be the output based on the path

InputStream in = Main.class.getResourceAsStream("Test.log"); //   /labo/Test.log
// > Hello from Labo
InputStream in = Main.class.getResourceAsStream("/Test.log"); //  /Test.log
// > Hello from Source Package

Code :

public class Main {
    public static void main(String[] args ) throws Exception{
        String[] paths = {"/Test.log", "Test.log"};
        for(String path : paths)
            readPath(path);
    }

    static void readPath(String path) throws Exception{
        InputStream in = Main.class.getResourceAsStream(path);
        InputStreamReader reader = new InputStreamReader(in);
        int i = -1;
        System.out.println(path + " : ");
        while((i = reader.read()) > -1){
            System.out.print((char)i);
       public }
        System.out.println();
    }
}

Output :

/Test.log : 
Hello from the Source Package
Test.log : 
Hello from Labo