如何在if语句中使用Try-with-resources? [英] How to use Try-with-resources with if statement?

问题描述

我有简单的代码:

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

    String line;

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

我想写这样的东西:

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

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

    String line;

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

它允许我重用FileReader.是否有可能?如果不是，如何正确重用FileReader?如果重要的话，我使用java 8.

It is allows me to reuse FileReader. Is it possible? If not, how to correctly reuse FileReader? I use java 8, if it is important.

推荐答案

您始终必须定义try-with-resources块的新变量部分. 这是Java 7/8中当前实现的局限性.在Java 9中，他们考虑支持您的本地需求.

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.

不过，您可以使用以下小技巧:

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) {
            ////
        }
    }
}

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