File IO: Difference between revisions
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==Reading from a file== | ==Reading from a file== | ||
==Writing to a file== | |||
===Simple === | ===Simple === |
Revision as of 02:56, 18 September 2004
Introduction
This article describes local file input/output in Javascript.
You access the filesystem using Mozilla XPCOM components. The list of components used for local IO is available at XulPlanet.com.
Available libraries
There are a few JavaScript wrappers for IO XPCOM components. See JSLib and MonkeeSage's IO module. MonkeeSage's module is much smaller and very easy to use (simple examples are included in the module).
Snippets using XPCOM directly
Creating a file object ("opening" files)
var file = Components.classes["@mozilla.org/file/local;1"]. createInstance(Components.interfaces.nsILocalFile); file.initWithPath("/home");
Note: the path passed to initWithPath() should be in 'native' form (eg. "C:\\Windows"). If you need to use file:// URIs as initializers, see below.
Getting special files
// get profile directory var file = Components.classes["@mozilla.org/file/directory_service;1"]. createInstance(Components.interfaces.nsIProperties). get("ProfD", Components.interfaces.nsIFile);
Here are some strings you can put in place of "ProfD" (stolen from MonkeeSage's IO module comments)
String | Meaning |
---|---|
ProfD | profile directory |
DefProfRt | user (e.g., /root/.mozilla) |
UChrm | %profile%/chrome |
DefRt | installation |
PrfDef | %installation%/defaults/pref |
ProfDefNoLoc | %installation%/defaults/profile |
APlugns | %installation%/plugins |
AChrom | %installation%/chrome |
ComsD | %installation%/components |
CurProcD | installation (usually) |
Home | OS root (e.g., /root) |
TmpD | OS tmp (e.g., /tmp) |
Look in the Source for other strings available: [1] [2].
nsIFile and path strings
You can use nsIFile::path to get platform-specific path string, eg. C:\Windows\System32 or /usr/share. If you want to get a file:// URL of a file or an nsIFile from file:// URL, you need to use nsIFileProtocolHandler:
// file is nsIFile var URL = Components.classes["@mozilla.org/network/protocol;1?name=file"]. createInstance(Components.interfaces.nsIFileProtocolHandler). getURLSpecFromFile(file);
Note: do not use nsILocalFile::persistentDescriptor to get the file path!
Also note that generally you don't need to use nsIFile::path. Use nsIFile directly wherever possible. An example below shows how you should save a path in user prefs.
Saving path in a userpref
This snippet shows the right way to save a file path in user preferences:
// |file| is nsILocalFile var prefs = Components.classes["@mozilla.org/preferences-service;1"]. getService(Components.interfaces.nsIPrefService). getBranch("extensions.myext."); prefs.setComplexValue("filename", Components.interfaces.nsILocalFile, file); /* You can read it later with this statement: var file = prefs.getComplexValue("filename", Components.interfaces.nsILocalFile); */
Get a file in given directory
Assume, file is an nsIFile pointing to some directory (f.e. a user profile directory). You can use this code: file.append("myfile.txt"); - to make file point to myfile.txt inside that directory.
Notes: avoid using dir.path+"\\"+"myfile.txt", as it is not cross-platform code. Using something like ((path.search(/\\/) != -1) ? path + "\\" : path + "/") + "myfile.txt"; is possible, but the nsIFile::append() is much easier to read and is guaranteed to work on all platforms Mozilla itself works.
Traverse directories
todo
Reading from a file
Writing to a file
Simple
// file is nsIFile var data = ""; var fstream = Components.classes["@mozilla.org/network/file-input-stream;1"] .createInstance(Components.interfaces.nsIFileInputStream); var sstream = Components.classes["@mozilla.org/scriptableinputstream;1"] .createInstance(Components.interfaces.nsIScriptableInputStream); fstream.init(file, 1, 0, false); sstream.init(fstream); data += sstream.read(-1); sstream.close(); fstream.close(); alert(data);
Line by line
// open an input stream from file var istream = Components.classes["@mozilla.org/network/file-input-stream;1"] .createInstance(Components.interfaces.nsIFileInputStream); istream.init(file, 0, 1, null); istream.QueryInterface(Components.interfaces.nsILineInputStream); // read lines into array var line = {}, lines = {}, hasmore; do { hasmore = istream.readLine(line); lines.push(line.value); } while(hasmore); istream.close(); // do something with read data alert(lines);