使用Java替换文本文件中的字符串

Question

I have a text file (file.txt) which contains multiple lines:

/location/test/file.csv
/location/test1/file2.csv
/location/test2/file.exe

Using ECMA, I would like to replace all instance of "/" with "\\". However, the code below only replaces the first line and eliminate lines 2 and 3.

This is the result of the file.txt file after I run the code (as I said, lines 2 and 3 are missing):

\location\test\file.csv

Can anyone please help?

function ReadFile ()
{
var file = new java.io.BufferedReader(new java.io.FileReader("C:\\Test\\file.txt"));
var fileWriter = new java.io.FileWriter("C:\\Test\\file.txt",false);
while ((line = file.readLine()) != null) 
 {
println(line);
if (line.contains ("/"))
line = line.replace("/","\\");

fileWriter.write(line);
fileWriter.close();
 }
} 
ReadFile ();

Answer 1

JavaScript String object has a replace method that takes a regular expression that can replace characters in a String. However, the Java in your JavaScript won't work because you are mixing up two languages.

http://www.w3schools.com/jsref/jsref_replace.asp

Answer 2

The problem is that you're writing over the file as you're reading it, so as soon as your first write(line) completes, the file no longer has the next two lines. Either use a second, temporary file to write to until you've finished processing the file, or keep a list/array of all the new lines in memory, and then write out the file at the end.

I'm really curious to know, though, how you managed to get your current program to even run. In my experience, Java and ECMA/Javascript are two completely separate languages, but it looks like you're using javascript code against Java libraries. What's up with that?

Answer 3

So I managed to run this code using Rhino. It does in fact run. I made some changes to filenames in order to get it running on my mac, but it is essentially the same code:

function ReadFile () {
  var file = new java.io.BufferedReader(new java.io.FileReader("file"));
  var fileWriter = new java.io.FileWriter("file2",false);
  while ((line = file.readLine()) != null) {
    if (line.contains ("/"))
      line = line.replace("/","\\");

    fileWriter.write(line + "\n");
 }
 fileWriter.close();
 file.close();
}
ReadFile ();

So the bugs you had were:

1. Reading and writing to the same file. This is awkward using streams. Basically, don't do it. I changed it to write to file2.
2. Closing the writer inside your reader loop. Close the writer at the end, once closed, you can no longer write to it.
3. Not closing the file you are reading from.

For those interested in how I got this running, on OS X, using rhino:

brew install rhino
rhino example.js

I had to remove the println because that wasn't recognised but that wasn't a critical part. JS on the JVM. Fun! Except nothing is async.....

There are other JS engines too, but rhino worked.