Java序列化:在try或finally块中关闭流？

Question

我正在查看Java序列化文章,并且在try块中而不是finally块中关闭流的示例中偶然发现了很多次.有人可以向我解释为什么会这样吗？

例:

import java.io.*;
public class DeserializeDemo {

    public static void main(String [] args) {
      Employee e = null;
      try {
         FileInputStream fileIn = new FileInputStream("/tmp/employee.ser");
         ObjectInputStream in = new ObjectInputStream(fileIn);
         e = (Employee) in.readObject();
         in.close();
         fileIn.close();
      } catch(IOException i) {
         i.printStackTrace();
         return;
      } catch(ClassNotFoundException c) {
         System.out.println("Employee class not found");
         c.printStackTrace();
         return;
      }

      System.out.println("Deserialized Employee...");
      System.out.println("Name: " + e.name);
      System.out.println("Address: " + e.address);
      System.out.println("SSN: " + e.SSN);
      System.out.println("Number: " + e.number);
   }
}

资料来源:http://www.tutorialspoint.com/java/java_serialization.htm

Answer 1

try-with-resources声明

try-with-resources语句是一个声明一个或多个资源的try语句.资源是在程序完成后必须关闭的对象.try-with-resources语句确保在语句结束时关闭每个资源.实现java.lang.AutoCloseable的任何对象(包括实现java.io.Closeable的所有对象)都可以用作资源.

以下示例从文件中读取第一行.它使用BufferedReader实例从文件中读取数据.BufferedReader是一个在程序完成后必须关闭的资源:

static String readFirstLineFromFile(String path) throws IOException {
    try (BufferedReader br =
                   new BufferedReader(new FileReader(path))) {
        return br.readLine();
    }
}

在此示例中,try-with-resources语句中声明的资源是BufferedReader.声明语句出现在try关键字后面的括号内.Java SE 7及更高版本中的BufferedReader类实现了java.lang.AutoCloseable接口.因为BufferedReader实例是在try-with-resource语句中声明的,所以无论try语句是正常完成还是突然完成(由于BufferedReader.readLine方法抛出IOException),它都将被关闭.

在Java SE 7之前,您可以使用finally块来确保关闭资源,无论try语句是正常还是突然完成.以下示例使用finally块而不是try-with-resources语句:

static String readFirstLineFromFileWithFinallyBlock(String path)
                                                     throws IOException {
    BufferedReader br = new BufferedReader(new FileReader(path));
    try {
        return br.readLine();
    } finally {
        if (br != null) br.close();
    }
}

来源=> http://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html