Java try with resources语法使用指南

try (资源声明) {
    // 使用资源
} catch (异常类型 变量) {
    // 处理异常
}

try (FileInputStream fis = new FileInputStream("data.txt")) {
    int data = fis.read();
    while (data != -1) {
        System.out.print((char) data);
        data = fis.read();
    }
} catch (IOException e) {
    System.err.println("读取文件出错：" + e.getMessage());
}
// fis会在此自动关闭，无需手动调用close()

try (
    FileInputStream in = new FileInputStream("input.txt");
    FileOutputStream out = new FileOutputStream("output.txt")
) {
    byte[] buffer = new byte[1024];
    int length;
    while ((length = in.read(buffer)) > 0) {
        out.write(buffer, 0, length);
    }
} catch (IOException e) {
    System.err.println("复制文件失败：" + e.getMessage());
}
// in 和 out 都会被自动关闭

try (
    Resource r1 = new Resource("r1");
    Resource r2 = new Resource("r2")
) {
    // 执行操作
}

public class MyResource implements AutoCloseable {
    public MyResource() {
        System.out.println("资源已打开");
    }

    public void doWork() {
        System.out.println("正在工作...");
    }

    @Override
    public void close() {
        System.out.println("资源已关闭");
    }
}

try (MyResource res = new MyResource()) {
    res.doWork();
}
// 输出：
// 资源已打开
// 正在工作...
// 资源已关闭