Gson 流关闭

Question

Does the stream close when you use something like:

gson.toJson(obj, new FileWriter("C:\\fileName.json"));

or is it better to to this:

        try (Reader reader = new FileReader("c:\\test\\staff.json")) {

            // Convert JSON File to Java Object
            Staff staff = gson.fromJson(reader, Staff.class);

            // print staff 
            System.out.println(staff);

        } catch (IOException e) {
            e.printStackTrace();
        }

I know the try block closes the stream, but does ths first example also close the stream?

Code taken from Mkyong

Answer 1

FileWriter implements AutoClosable so it needs to be closed. Not naming the variable will not close it automatically.

Answer 2

Does the stream close when you use something like:

 gson.toJson(obj, new FileWriter("C:\\\\fileName.json"));

It does not. You should close it using try-with-resources, or a try-catch-finally block.

---

Since JDK 7, the preferred way to close an AutoClosable is to use try-with-resources (like in your second snippet):

try (FileWriter writer = new FileWriter("C:\\fileName.json")) {
    gson.toJson(obj, writer);
} catch (IOException e) {
    e.printStackTrace();
}

Or you could call close() using a try-catch-finally block:

FileWriter writer = null;
try {
    writer = new FileWriter("C:\\fileName.json");
    gson.toJson(obj, writer);
} catch (IOException e) {
    e.printStackTrace();
} finally {
    if (writer != null) {
        try {
            writer.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}