CODEWITHSUNDEEP
javaiosonarlint
HS447
HS447

Reputation: 81

Resources closed but sonarlint still showing resource not closed

I have defined Output stream like below OutputStream os=new FileOutputStream(file);

Tried to close the resource like below

if(os != null) {
    try {
       os.close();
    } catch (IOException e) {
       e.printStackTrace();
    }}

Still sonarlint showing "Use try-with-resources or close this "FileOutputStream" in a "finally" clause."

Upvotes: 2

Views: 927

Answers (2)

Dubas
Dubas

Reputation: 2876

If you are doing the operations in the same method it's important to put the close in a finally statement of a try that envolves the open part of the stream. This ensures that in case of failure (Exception) the stream is allways closed if required

Bad sonar code:

OutputStream os=new FileOutputStream(file);

... // your code operations with os

// If something is going really bad here and ends in exception the
// stream will never be closed

if(os != null) {
    try {
       os.close();
    } catch (IOException e) {
       e.printStackTrace();
    }
}

Better code:

OutputStream os = null;
try{
    os = new FileOutputStream(file);

    ... // your code operations with os

} finally{
    // The stream is allways closed at the end of the method execution
    if(os != null) {
        try {
           os.close();
        } catch (IOException e) {
           e.printStackTrace();
        }
    } 
 }

The best code (in case of Java 1.7 or upper)

try (OutputStream  os = new FileOutputStream(file)){

  ... // your code operations with os

  // The stream is allways closed at the end of the try block
}

Upvotes: 3

mkane
mkane

Reputation: 920

Try this instead. You do not do a close when using try with resources, that is automatically handled... i.e.

"The try-with-resources statement ensures that each resource is closed at the end of the statement."

try( OutputStream os=new FileOutputStream(file) ) {
    ....
}

Any resources declared within the brackets are closed automatically once the program flow has completed whether an exception is thrown or not..

Examples here : https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html

Upvotes: 1

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