Null pointer when reading a Properties file from another folder

Question

My application will check if a Properties file exists and create one if not.

try{
        // create new file

        String path="c:\\temp\\LaserController.properties";
        File file = new File(path);
        String comport = "Comport=COM1";
        String Parity = "parity=none";
        String baud = "baud=9600";
        String Stopbits = "StopBits=0";
        String databits = "DataBits=8";
           // if file doesnt exists, then create it
           if (!file.exists()) {
               file.createNewFile();



           FileWriter fw = new FileWriter(file.getAbsoluteFile());
           BufferedWriter bw = new BufferedWriter(fw);
           // write in file
           bw.write(comport);
           bw.newLine();
           bw.write(Parity);
           bw.newLine();
           bw.write(baud);
           bw.newLine();
           bw.write(Stopbits);
           bw.newLine();
           bw.write(databits);
           // close connection
           bw.close();
           }

But when i try to read the properties file like this i get a Null pointer.

else {
           Properties prop = new Properties();


            InputStream input = LaserControllerUI.class.getResourceAsStream("c:\\temp\\LaserController.properties");


            // load a properties file
            prop.load(input);

            // get the property value and print it out
            System.out.println(prop.getProperty(Comport+"comport"));
            System.out.println(prop.getProperty("Parity"));
            System.out.println(prop.getProperty("Baud"));
            input.close();

        }
     }catch(Exception e){
         System.out.println(e);
     }
}

It fails on the InputStream input line but i dont know why. the file exists and my application can access it because it put it there in the first place. What am i doing wrong?

The file has to be in a location that is accessible to users to change parameters.

`LaserControllerUI` ... where is this class defined and what does it do? — Tim Biegeleisen, Nov 10 '16 at 09:16

score 5 · Accepted Answer · answered Nov 10 '16 at 09:19

5

getResourceAsStream method needs a "class-path relative" name. You are providing an absolute path. Try to use FileInputStream instead.

E.g:

InputStream input = new FileInputStream("c:\\temp\\LaserController.properties");

answered Nov 10 '16 at 09:19

Sachin Gupta

7,805
4
30
45

1

"It fails on the InputStream input line" most alikely this is the case, after that is fixed, the OP should read my answer. +1 – Peter Lawrey Nov 10 '16 at 09:21

score 3 · Answer 2 · edited Nov 10 '16 at 11:39

3

I suggest using Properties.save() to ensure it is written in a format when can be read.

I suggest you look at the text file to see what was written.

BTW The properties are case sensitive. you write

Comport
parity
baud

but you read

Comport+"comport"
Parity
Baud

so they will all be null.

edited Nov 10 '16 at 11:39

Marcin Orlowski

72,056
11
123
141

answered Nov 10 '16 at 09:19

Peter Lawrey

525,659
79
751
1,130

Ok, done and fixed the capitalisation. It now prints out null but if i click on `comport` it shows the correct value written in the `properties` file `comport=COM1` – Display Name Nov 10 '16 at 09:39
@DisplayName I am guessing you shouldn't be looking up `Comport+"comport"` – Peter Lawrey Nov 10 '16 at 10:56
thats right i changet it to `comport` when i click on it in eclipse it will show me the properties but it doesnt print out "COM1" as expected. – Display Name Nov 10 '16 at 11:28
@DisplayName what does it show? – Peter Lawrey Nov 10 '16 at 11:29
I have added a screen grab to the question. – Display Name Nov 10 '16 at 11:39
@DisplayName ypu need to change it to "comport" not the variable `comport` as what you are doing is looking up that String as the key and no such key exists. – Peter Lawrey Nov 10 '16 at 11:44
1

Ah got you. Thanks very much that works! Its a steep learning curve for me. – Display Name Nov 10 '16 at 11:47

score 0 · Answer 3 · answered Nov 10 '16 at 09:45

0

Move that file to resource folder or add that folder as resource folder

getClass().getClassLoader().getResourceAsStream("LaserController.properties")

answered Nov 10 '16 at 09:45

Venkatesh Srinivas

21
2

Null pointer when reading a Properties file from another folder

3 Answers3