How to get file from classpath

MartinHilpert
Posts:3,374
Registered: 10/24/97

How to get File/InputStream from a file in CLASSPATH?   
Nov 26, 2003 3:14 AM

 

Referencing a file with the absolute path or relative to the current working directory works flawlessly. what if i don't know the path during compile time but only during runtime? i know the fileName (without path) during runtime, but don't know where it is located. I just know that it is in the CLASSPATH. SO i tried these two ways to get the InputStream for a fileName:

           try {                URL url = IOUtils.class.getResource(fileName);                result = url.openStream();            } catch (Exception e) { out(e); }                         //try to load from CLASSPATH:            if (result == null) {                try {                    URLClassLoader cl = (URLClassLoader) IOUtils.class.getClassLoader();                    URL url = cl.findResource(fileName);                    result = url.openStream();                } catch (Exception e) { out(e); }            }

but both don't find the file, even though the file is in the CLASSPATH (also checked correct spelling). is there another way to retrieve the File or InputStream object to a file in the CLASSPATH?

 

davidsingleton
Posts:193
Registered: 1/21/00

Re: How to get File/InputStream from a file in CLASSPATH?   
Nov 26, 2003 3:34 AM (reply 1 of 5)

 

Hallo,

yes, this is sometimes a difficult problem. I have sweated blood doing this as well. I think that the bast way is probably:

URL url = ClassLoader.getSystemResource(fileName);

 

MartinHilpert
Posts:3,374
Registered: 10/24/97

Re: How to get File/InputStream from a file in CLASSPATH?   
Nov 26, 2003 4:11 AM (reply 2 of 5)

 

nope that doesn't work. but i wrote my own method that loads the file from the classpath (which works :-) :

    /** * Get CLASSPATH entries. *  * @return List of all entries in the current CLASSPATH. */public static List getClassPath() {       List result = new ArrayList();              String classPath = System.getProperty("java.class.path");       StringBuffer sb = new StringBuffer();       for (int i = 0; i < classPath.length(); i++) { //for each character           if (classPath.charAt(i) == ';') {               result.add(sb.toString());               sb.setLength(0);           } else {               sb.append(classPath.charAt(i));           }       }//next character              if (!sb.equals("")) {           result.add(sb.toString());       }         return result;    }//getClassPath()     /**     * Try to open a valid InputStream from various sources (CLASSPATH, Filesystem, Jar, etc.)     *      * @param fileName Name of file to open.     * @return InputStream or null if not found/not possible.     */    public InputStream openInputStream(String fileName) {        InputStream result = null;         if (fileName != null) {            //try to load from URL:            try {                URL url = this.class.getResource(fileName);                result = url.openStream();            } catch (Exception e) { /* ignore */ }             //try to get from system:            if (result == null) {                try {                    URL url = ClassLoader.getSystemResource(fileName);                    result = url.openStream();                } catch (Exception e) { /* ignore */ }            }                        //try to load from CLASSPATH (JDK 1.2):            if (result == null) {                try {                    URLClassLoader cl = (URLClassLoader) IOUtils.class.getClassLoader();                    URL url = cl.findResource(fileName);                    result = url.openStream();                } catch (Exception e) { /* ignore */ }            }             //try to load from CLASSPATH (JDK 1.1):            if (result == null) {                try {                    ClassLoader cl = this.class.getClassLoader();                    result = cl.getResourceAsStream(fileName);                } catch (Exception e) {                    //ignore                }            }                        //try to load from current working directory:                        if (result == null) {                try {                    result = new FileInputStream(fileName);                } catch (Exception e) { /* ignore */ }            }                //try to load from user home directory:            if (result == null) {                try {                    result = new FileInputStream(System.getProperty("user.dir") + File.separatorChar + fileName);                } catch (Exception e) { /* ignore */ }            }             //try to load from CLASSPATH:            if (result == null) {                try {                    List classPath = getClassPath();                    Iterator iterator = classPath.iterator();                    while (iterator.hasNext()) {                        String classPathFileName = (String) iterator.next();                        File file = new File(classPathFileName);                        if (file.exists()) {                            if (file.isFile()) {                                //check if CLASSPATH file is the file we're looking for:                                if (file.getName().equals(fileName)) {                                    result = new FileInputStream(classPathFileName);                                    break;                                } else {                                    //perhaps the current file is an archive containing the file:                                    ZipInputStream zis = new ZipInputStream(new FileInputStream(classPathFileName));                                    ZipEntry ze = null;                                    for (ze = zis.getNextEntry(); ze != null; ze = zis.getNextEntry()) {                                        if (ze.getName().equals(fileName.replace(File.separatorChar, '/'))) {                                            result = new DataInputStream(zis);                                            break;                                        }                                    }//next ZipEntry                                }                            } else if (file.isDirectory()) {                                 // if class path is directory, check if file found along that path                                 file = new File(classPathFileName + File.separatorChar + fileName);                                 if (file.isFile()) {                                    result = new DataInputStream(new FileInputStream(file));                                    break;                                }                            }                        }//else: file does not exist                    }//next CLASSPATH entry                } catch (Exception e) { /* ignore */ }            }        }//else: input unavailable         return result;    }//openInputStream()

 

edsonw
Posts:3,055
Registered: 18/06/98

Re: How to get File/InputStream from a file in CLASSPATH?   
Nov 26, 2003 4:16 AM (reply 3 of 5)

 

Great!
But replace

           if (classPath.charAt(i) == ';') {

by something that is more operating-system independent, like comparing with a variable that holds the value of System.getProperty("path.separator").

 

Andi_Berlin
Posts:47
Registered: 9/1/03

Re: How to get File/InputStream from a file in CLASSPATH?   
Nov 26, 2003 4:19 AM (reply 4 of 5)

 

I' m using

Util.class.getClassLoader().getResourceAsStream("myFile.txt");

and it works.

 

MartinHilpert
Posts:3,374
Registered: 10/24/97

Re: How to get File/InputStream from a file in CLASSPATH?   
Nov 26, 2003 5:22 AM (reply 5 of 5)

 

even better:

    /** * Get CLASSPATH entries. *  * @return List of all entries in the current CLASSPATH. */public static List getClassPath() {       List result = new ArrayList();              String classPath = System.getProperty("java.class.path");       StringBuffer sb = new StringBuffer();       char pathSeparator = ';'; //default       String ps = System.getProperty("path.separator");       if (ps != null && ps.length() > 0) {           pathSeparator = ps.charAt(0);       }        StringCharacterIterator sci = new StringCharacterIterator(classPath);       char c = sci.first();       while (c != CharacterIterator.DONE) {           if (c == pathSeparator) {               result.add(sb.toString());               sb.setLength(0);           } else {               sb.append(c);           }           c = sci.next();       }//next character              if (!sb.equals("")) {           result.add(sb.toString());       }              return result;    }//getClassPath()