Java 文件 I/O 的良好实践
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Good practice in Java File I/O
提问by Happy Mittal
I am trying to read integers from a file, apply some operation on them and writing those resulting integers to another file.
我试图从文件中读取整数，对它们应用一些操作并将这些结果整数写入另一个文件。
// Input
FileReader fr = new FileReader("test.txt");
BufferedReader br = new BufferedReader(fr);
Scanner s = new Scanner(br);
// Output
FileWriter fw = new FileWriter("out.txt");
BufferedWriter bw = new BufferedWriter(fw);
PrintWriter pw = new PrintWriter(bw);
int i;
while(s.hasNextInt())
{
i = s.nextInt();
pw.println(i+5);
}
I want to ask is it a good practice to wrap these input and output streams like this?
I am new to java and on internet, I saw lots of other ways of I/O in files. I want to stick to one approach so is above the best approach ?
我想问一下，像这样包装这些输入和输出流是一个好习惯吗？
我是 Java 和互联网的新手，我在文件中看到了很多其他的 I/O 方式。我想坚持一种方法，所以是最好的方法吗？
回答by Kumar Vivek Mitra
-Well consider that you went shopping into a food mall, Now what you do usually, pick-up each item from the selves and then go to the billing counter then again go to the selves and back to billing counter ....?? Or Store all the item into a Cart then go to the billing counter.
-想想你去食品商场购物，现在你通常做的事情是，从自己那里拿起每件物品，然后去计费柜台，然后再去自己，然后回到计费柜台......？？或将所有物品放入购物车，然后前往计费柜台。
-Its similar here in Java, Filesdeal with bytes, and Bufferdeals with characters, so there is a conversion of bytes to characters and trust me it works well, there will not be any noticeable overhead.
-它在 Java 中类似，Files处理字节和Buffer处理字符，因此将字节转换为字符，相信我它运行良好，不会有任何明显的开销。
So to Read the File:
所以要读取文件：
File f = new File("Path");
FileReader fr = new FileReader(f);
BufferedReader br = new BufferedReader(fr);
So to Write the File:
所以要写文件：
File f = new File("Path");
FileWriter fw = new FileWriter(f);
BufferedWriter bw = new BufferedWriter(fw);
And when you use Scannerthere is no need to use BufferedReader
当你使用时Scanner，不需要使用BufferedReader
回答by manfcas
Keep in mind that the design of those classes is based on the Decorator design pattern. A good practice is to close all instances of java.io.Closeablein a finallyblock. For example:
请记住，这些类的设计基于装饰器设计模式。一个好的做法是关闭的所有实例java.io.Closeable的finally块。例如：
Reader r = null;
Scanner s = null;
try {
r = new FileReader("test.txt");
s = new Scanner(r);
// Do your stuff here.
} finally {
if (r != null)
r.close();
if (s != null)
s.close();
}
or, if you are using Java 7 or higher:
或者，如果您使用的是 Java 7 或更高版本：
try (
Reader r = new FileReader("test.txt");
Scanner s = new Scanner(r)
) {
// Do your stuff here.
}
回答by clinton
Scanner does not need the BufferedReader. You can wrap it over the FileReader.
Scanner 不需要 BufferedReader。您可以将它包装在 FileReader 上。
Scanner s = new Scanner(new FileReader("test.txt"));
While using the scanner its better to assume that the source contains various content. Its good to close the scanner after using it.
在使用扫描仪时，最好假设来源包含各种内容。用完后关闭扫描仪就好了。
while(s.hasNext()){
if(s.hasNextInt())
int i = s.nextInt();
s.next();
}
s.close();
回答by PermGenError
you dont really need BuffredWriterwhen you are using PrintWriterto write character data, printwriterhas a constructor which takes filewriteras an argument. and dont need a scannerto readfrom a fileyou could acheive it using bufferedreaderitself.
BuffredWriter当你PrintWriter用来写字符数据时，你真的不需要，printwriter有一个构造函数，它filewriter作为一个argument. 并且不需要一个scannerto readfrom afile你可以使用bufferedreader它自己来实现它。
FileReader fr = new FileReader("test.txt");
BufferedReader br = new BufferedReader(fr);
while((line=br.readLine())!=null){
//do read operations here
}
FileWriter fw = new FileWriter("out.txt");
PrintWriter pw = new PrintWriter(fw);
pw.println("write some data to the file")
回答by Angel
I usually do this:
我通常这样做：
String inputFileLocation = "Write it here";
BufferedReader br = new BufferedReader(new FileReader(new File(fileLocation)));
while((line=br.readLine())!=null){
//Scanner operations here
}
String outputFileLocation = "Here";
PrintWriter pr = new PrintWriter(new FileWriter(new File(outputFileLocation)));
