CODEWITHSUNDEEP
javaeclipsenullpointerexception
Archie
Archie

Reputation: 120

Java Trying to debug NullPointerException

I have this java code and caught a nullPointerException when I run it. Through debugging using eclipse, I found out that msiLine parameter is null but I can't find out why.

                String msiAbsolutePath = msiFiles.getAbsolutePath();
                String filePath = msiAbsolutePath.substring(0,msiAbsolutePath.lastIndexOf(File.separator));
                new File(filePath+"/Emboss").mkdir();
                new File(filePath+"/Report").mkdir();
                File files = sort(msiFiles,filePath);

                BufferedReader msiReader = new BufferedReader(new FileReader(files));
                BufferedReader embReader = new BufferedReader(new FileReader(embFiles));
                String[] msiTokens = msiFiles.getName().split("\\.(?=[^\\.]+$)");
                String[] embTokens = embFiles.getName().split("\\.(?=[^\\.]+$)");
                final String msiFileName = msiTokens[0];
                final String embFileName = embTokens[0];
                Date date = new Date();
                DateFormat dateFormatName = new SimpleDateFormat("MMdd");
                PrintWriter msiWrite = new PrintWriter(new BufferedWriter(new FileWriter(filePath+"/Emboss/"+msiFileName+".PRN")));
                PrintWriter embWrite = new PrintWriter(new BufferedWriter(new FileWriter(filePath+"/Emboss/"+embFileName+".PRN")));
                PrintWriter reportWrite = new PrintWriter(new BufferedWriter(new FileWriter(filePath+"/Report/CS"+dateFormatName.format(date)+".RPT")));


                cnt=totalLines=0;
                //String msiLine = msiReader.readLine();
                String msiLine="";
                String embLine = embReader.readLine();
        here>>> for(msiLine = msiReader.readLine(); msiLine.length() >= 60; msiLine = msiReader.readLine())
                {
                    embLine = embReader.readLine();
                    msiWrite.print();
                    :
                    :

                    }
                    statMessage = "Completed " + current + " out of " + lengthOfTask + ".";
                }
                :
                :
            }catch(IllegalStateException | IOException | NullPointerException d){
                d.printStackTrace();
            }
        }
    }

    File sort(File file, String filepath){
        File files = new File(filepath + "\\tempMSIfile.msi");
        try{

            BufferedReader reader = new BufferedReader(new FileReader(file));
            Map<String, String> map=new TreeMap<String, String>();
            String line=reader.readLine();
            for(line = reader.readLine(); line.length() >= 60; line = reader.readLine()){
                map.put(getField(line),line);
            }
            reader.close();
            PrintWriter writer = new PrintWriter(new BufferedWriter(new FileWriter(files)));
            for(String val : map.values()){
                writer.print("" +val);  
                writer.print(NEWLINE);
            }
            writer.close();

        }catch(IllegalStateException | IOException | NullPointerException d){
            LOG.fine("Error, " + d.getMessage());
        }
        return files;
    }

    String getField(String line) {
        return line.substring(10, 26);//extract value you want to sort on
    }

Can somebody explain to me why is the msiLine is null?

I think it involves the File files = sort(msiFiles,filePath); but the eclipse report that files parameter does have the correct file/thing(?) assigned to it.

In case anyone wondering, tempMSIfile.msi is not empty.

Upvotes: 0

Views: 597

Answers (3)

fge
fge

Reputation: 121712

Reader's .readLine() returns null when the end of input is reached. As such, your condition:

msiLine.length() < 60`

can trigger a NullPointerException. Change it to add a null test before testing the length.

EDIT: as @KubaSpatny points out, change the condition to:

msiLine != null && msiLine.length() < 60

Or, as your comment seems to suggest, put msiLine != null as the condition, and as the first instruction in the loop:

if (msiLine.length() < 60)
    continue; // or break;, depending on what you want to do

Your sort() method suffers the same problem.

Upvotes: 3

f1sh
f1sh

Reputation: 11934

Read the documentation for readLine():

Returns: A String containing the contents of the line, not including any line-termination characters, or null if the end of the stream has been reached

That means: if msiLine is null inside the loop, the file has been read completely. In that case, exit the loop:

if(msiLine==null){
   break;
}

or add the check to your loop header.

Upvotes: 2

Saket
Saket

Reputation: 3129

Javadoc for java.io.BufferedReader#readLine() states that it returns

 A String containing the contents of the line, not including
 any line-termination characters, or null if the end of the
 stream has been reached

You are probably encountering the end of the file. Add a null check for msiLine to check when you reach the end of the file.

Upvotes: 0

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