如何在 if 语句中使用 try-with-resources？

Question

I have the simple code:

try (FileReader file = new FileReader(messageFilePath);
     BufferedReader reader = new BufferedReader(file)) {

    String line;
    while ((line = reader.readLine()) != null) {
        ////
    }
} 

I want to write something like this:

FileReader file = null;
///.....

try (file = (file == null ? new FileReader(messageFilePath) : file);
     BufferedReader reader = new BufferedReader(file)) {

    String line;
    while ((line = reader.readLine()) != null) {
        ////
    }
} 

It would allow me to reuse FileReader . Is it possible? If not, how to correctly reuse FileReader ?

PS
I use Java 8, if it is important.

Answer 1

You always have to define a new variable part of try-with-resources block. It is the current limitation of the implementation in Java 7/8 . In Java 9 they consider supporting what you asked for natively.

You can however use the following small trick:

public static void main(String[] args) throws IOException {
    FileReader file = null;
    String messageFilePath = "";

    try (FileReader reader = file = (file == null ? new FileReader(messageFilePath) : file);
            BufferedReader bufReader = new BufferedReader(file)) {

        String line;

        while ((line = bufReader.readLine()) != null) {
            ////
        }
    }
}