Issues in scope of variables while using try-catch in Java

Question

I have a class PDF which implements an interface fileReader.

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

public class PDF implements fileReader {
    @Override
    public byte[] readFile(File pdfDoc) {
        if (!pdfDoc.exists()) {
            System.out.println("Could not find" + pdfDoc.getName() + " on the specified path");
            return null;
        }
        FileInputStream fin = null;
        try {
            fin = new FileInputStream(pdfDoc);
        } catch (FileNotFoundException e) {
            System.out.println("");
            e.printStackTrace();
        }
        byte fileContent[] = new byte[(int) pdfDoc.length()];
        try {
            fin.read(fileContent);
        } catch (IOException e) {
            e.printStackTrace();
        }
        return fileContent;
    }
}

import java.io.File;
public interface fileReader {
    <T> T readFile(File fileObject);
}

I notice that there are scope issues for variables fin.

Another implementation I made was:

public byte[] readFile1(File pdfDoc) {
        if (!pdfDoc.exists()) {
            System.out.println("Could not find" + pdfDoc.getName() + " on the specified path");
            return null;
        }
        FileInputStream fin = null;
        try {
            fin = new FileInputStream(pdfDoc);
            byte fileContent[] = new byte[(int) pdfDoc.length()];
            try {
                fin.read(fileContent);
            } catch (IOException e) {
                System.out.println("");
                e.printStackTrace();
            }
        } catch (FileNotFoundException e) {
            System.out.println("");
            e.printStackTrace();
        }
        return fileContent;
    }

But now I could not access fileContent.

How can I combine the try-catches so that I don't have scope problems? Can there be a better design approach to this problem? I have to make functions for reading three different types of file.

Answer 1

Since Java 7 you can combine the try-catch as follows:

    FileInputStream fin = null;
    try {
        fin = new FileInputStream(pdfDoc);
        byte fileContent[] = new byte[(int) pdfDoc.length()];
        fin.read(fileContent);
    } catch (IOException | FileNotFoundException e) {
        System.out.println("");
        e.printStackTrace();
    }

Which, in my opinion, makes the code cleaner and variable scopes more obvious.

Answer 2

You can nest the try catch statements:

    try {
       FileInputStream fin = new FileInputStream(pdfDoc);
       byte fileContent[] = new byte[(int) pdfDoc.length()];
       try {
          fin.read(fileContent);
          return fileContent;
       } catch (IOException e) {
         e.printStackTrace();
       } finally {
         fin.close();
       }

    } catch (FileNotFoundException e) {
        System.out.println("");
        e.printStackTrace();
    }
    return null;

Note that I added a close() in a finally clause to clean up. And also returning null is probably not what you want in case of error, but that's application specific.

Answer 3

You can have one try with multiple catch blocks.

try {
    //do stuff
}
catch (FileNotFoundException e) {
        System.out.println("");
        e.printStackTrace();
}
catch (IOException e) {
        e.printStackTrace();
}

Answer 4

You can modify this part:

        FileInputStream fin = null;
        try {
            fin = new FileInputStream(pdfDoc);
        } catch (FileNotFoundException e) {
            System.out.println("");
            e.printStackTrace();
        }
        byte fileContent[] = new byte[(int) pdfDoc.length()];
        try {
            fin.read(fileContent);
        } catch (IOException e) {
            e.printStackTrace();
        }

By

{
......
       FileInputStream fin = null;
       byte fileContent[]=null;
        try {
            fin = new FileInputStream(pdfDoc);
            fileContent = new byte[(int) pdfDoc.length()];
            fin.read(fileContent);
        } catch (FileNotFoundException e) {
            System.out.println("");
            e.printStackTrace();
        }catch (IOException e) {
            e.printStackTrace();
        }
        return fileContent
    }

Answer 5

I would write like this:

public byte[] readFile(File pdfDoc) {
    if (!pdfDoc.exists()) {
        System.out.println("Could not find" + pdfDoc.getName() + " on the specified path");
        return null;
    }
    FileInputStream fin = null;
    byte fileContent[] = new byte[(int) pdfDoc.length()];

    try {
        fin = new FileInputStream(pdfDoc);
        fin.read(fileContent);
    } catch (FileNotFoundException e) {
        System.out.println("");
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (null != fin) {
            fin.close();
        }
    }   
    return fileContent;
}