CODEWITHSUNDEEP
javatry-catch
user396707
user396707

Reputation: 439

Java 7 try-with-resources - what can be in try clause

I know that there must be a variable declaration associated with the resource in the try clause.

But as well being assigned a usual resource instantiation, could it instead be assigned an already existing resource eg :

public String getAsString(HttpServletRequest request) throws Exception {   
    try (BufferedReader in = request.getReader(); ){ 
        etc 
    } 
}

ie. will the BufferedReader be closed automatically just like resources instantiated directly in the try clause ?

Upvotes: 1

Views: 88

Answers (3)

Anil Bhaskar
Anil Bhaskar

Reputation: 3978

Yes, BufferedReader will be closed automatically.

Since Java 7, Interface AutoCloseable is added as a SuperInterface of Closeable, so all implementing classes of Closeable (ie. Resource classes) interface automatically inherit AutoCloseable interface.

Upvotes: 1

Sweeper
Sweeper

Reputation: 271565

We can test whether this is true using this code:

class Main {
    public static void main(String[]args) throws Exception {
        AutoCloseable _close = getCloseable()
       try (AutoCloseable close = _close) {
           // ...
       }

    }

    public static AutoCloseable getCloseable() {
        return new MyCloseable();
    }
}

class MyCloseable implements AutoCloseable {

    @Override
    public void close() {
        System.out.println("Closing");
    }
}

The output is "Closing". This means that indeed, AutoCloseables that are created before the try block will still be closed after the try block.

Actually, Java does not care what you put in the () of the try block, as long as it implements AutoCloseable. At runtime, the expression will be automatically evaluated to a value, whether it is a new expression or not.

Upvotes: 2

Eugene
Eugene

Reputation: 120858

Yes. Anything that is AutoCloseable will call the close method. try-with-resource will do that.

Upvotes: 4

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