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EFFICIENTLY Load classes from jar file INSIDE jar file

Java programmer here.
I'm trying to make a "plugin system" in java, and I would like ot make it so that the user can import their own java libraries if they needed to so they are not limited to only have my plugin loading application in their build path.
I was planning on allowing the user to make a folder called "lib" in their project, which is where they would put all the other libraries they needed, so they can then add those to the build path with the application erroring when loading all the necessary plugins. But, I am having trouble to do so.
Here is an example plugin jar file I have, that is structured the way I want it to be:
Plugin.jar
|---org
|---pluginpackage
|---PluginMainClass.class
|---lib
|---user-lib.jar
|---libpackage
|---InterfaceA.class
|---ClassB.class
|---...
|---plugin-description.xml
What I was wondering is this: What would be the most efficient way to load all the libraries the user has loaded inside the "lib" folder?
This is the current code I have, but it takes longer than desired to load the libraries:
private void readLibraryInJar(JarInputStream jarLibraryInputStream, File dirOut) throws IOException {
if (jarLibraryInputStream == null)
return;
JarEntry entry = null;
while ((entry = jarLibraryInputStream.getNextJarEntry()) != null) {
final String jarPath = entry.getName().trim();
if (jarPath.endsWith(".class")) {
File f = new File(dirOut, jarPath);
if (!f.exists()) {
if (!f.getParentFile().exists()) {
f.getParentFile().mkdirs();
}
f.createNewFile();
}
byte[] buffer = new byte[1024 * 100];
FileOutputStream out = new FileOutputStream(f);
int len;
while ((len = jarLibraryInputStream.read(buffer)) > 0) {
out.write(buffer, 0, len);
}
out.close();
}
}
}
The above code reads each class file inside the desired library and copy's its content's into a new file. I know that a more efficient way is out there somewhere (e.g. Apache Tomcat project can have a "lib" folder), so I was wondering if I could load the library jar file more effeciently than I currently do (planning on using URLClassLoader to load it, so if you could transform it into a URL that would be awesome, but if that is impossible, I am still okay with any way more efficient than my current one.)
Thanks in advance!

Extract Files from Java project, during run proccess

I am trying to extract few files contained in the java project into a certain path, lets say "c:\temp".
I tried to use this example :
String home = getClass().getProtectionDomain().
getCodeSource().getLocation().toString().
substring(6);
JarFile jar = new JarFile(home);
ZipEntry entry = jar.getEntry("mydb.mdb");
File efile = new File(dest, entry.getName());
InputStream in =
new BufferedInputStream(jar.getInputStream(entry));
OutputStream out =
new BufferedOutputStream(new FileOutputStream(efile));
byte[] buffer = new byte[2048];
for (;;) {
int nBytes = in.read(buffer);
if (nBytes <= 0) break;
out.write(buffer, 0, nBytes);
}
out.flush();
out.close();
in.close();
I think I am doing it wrong and, this code probably looking for a specific jar but not in my project directory. I prefer to figure a way that can retrieve my files from resources package, inside the project folder and extract it to specific folder i choose.
I am using Eclipse, 1.4 J2SE library.

Well, it's hard to guess what's wrong without any code examples.
But as for pair of random guesses I could tell that sometimes you get this kind of error when the file is locked by earlier instance of your program which is still running. Make sure you've got only one running instance of Eclipse.
Also you can try to refresh the project folder by right click --> refresh to sync your file system with Eclipse's internal file system: when it comes to Eclipse, multiple refresh/rebuild someway magically solves project problems :)

Get file in the resources folder in Java

I want to read the file in my resource folder in my Java project. I used the following code for that
MyClass.class.getResource("/myFile.xsd").getPath();
And I wanted to check the path of the file. But it gives the following path
file:/home/malintha/.m2/repository/org/wso2/carbon/automation/org.wso2.carbon.automation.engine/4.2.0-SNAPSHOT/org.wso2.carbon.automation.engine-4.2.0-SNAPSHOT.jar!/myFile.xsd
I get the file path in the maven repository dependency and it is not getting the file. How can I do this?

You need to give the path of your res folder.
MyClass.class.getResource("/res/path/to/the/file/myFile.xsd").getPath();

Is your resource directory in the classpath?
You are not including resource directory in your path:
MyClass.class.getResource("/${YOUR_RES_DIR_HERE}/myFile.xsd").getPath();

A reliable way to construct a File instance from the resource folder is it to copy the resource as a stream into a temporary File (temp file will be deleted when the JVM exits):
public static File getResourceAsFile(String resourcePath) {
try {
InputStream in = ClassLoader.getSystemClassLoader().getResourceAsStream(resourcePath);
if (in == null) {
return null;
}
File tempFile = File.createTempFile(String.valueOf(in.hashCode()), ".tmp");
tempFile.deleteOnExit();
try (FileOutputStream out = new FileOutputStream(tempFile)) {
//copy stream
byte[] buffer = new byte[1024];
int bytesRead;
while ((bytesRead = in.read(buffer)) != -1) {
out.write(buffer, 0, bytesRead);
}
}
return tempFile;
} catch (IOException e) {
e.printStackTrace();
return null;
}
}

It is not possible to access resources of other maven modules. So you need to provide your resource myFile.xsd in your src/main/resources or src/test/resources folder.

The path is correct, though not on the file system, but inside the jar. That is, because the jar was running. A resource never is guaranteed to be a File.
However if you do not want to use resources, you can use a zip file system. However Files.copy would suffice to copy the file outside the jar. Modifying the file inside the jar is a bad idea. Better use the resource as "template" to make an initial copy in the user's home (sub-)directory (System.getProperty("user.home")).

In maven project, lets assume that, we have the file whose name is "config.cnf" and it's location is below.
/src
/main
/resources
/conf
config.cnf
In IDE (Eclipse), I access this file by using ClassLoader.getResource(..) method, but if I ran this application by using jar, I always across "File not found" exception. Finally, I wrote a method which accessing the file by looking at where app works.
public static File getResourceFile(String relativePath)
{
File file = null;
URL location = <Class>.class.getProtectionDomain().getCodeSource().getLocation();
String codeLoaction = location.toString();
try{
if (codeLocation.endsWith(".jar"){
//Call from jar
Path path = Paths.get(location.toURI()).resolve("../classes/" + relativePath).normalize();
file = path.toFile();
}else{
//Call from IDE
file = new File(<Class>.class.getClassLoader().getResource(relativePath).getPath());
}
}catch(URISyntaxException ex){
ex.printStackTrace();
}
return file;
}
If you call this method by sending "conf/config.conf" param, you access this file from both jar and IDE.

Webapplication: Delete files during runtime

I am developing a webapp (for mobile phones). There is one xhtml page, where I want to show a picture, which is stored locally on my hard drive (for example: D:\pictures\test.jpg).
Since browsers block images when they are located on a local harddrive, I wrote a method in my javabean, where the picture, stored on the localHD, is copied to the webApp directory, when the user enters the xhtml page. After the user leaves the page, the copied file inside the webapp should be deleted.
So when I'm running my app, copying works perfectly and the pictures are displayed correctly. However, when the files should get deleted, I get this errormessage:
java.nio.file.FileSystemException: D:\WebAppPath\src\main\webapp\resources\pics\test.jpg:
The process cannot be accessed because the file is being used by another process.
Strangely enough, after stopping and restarting the application I can delete the same image if it is still in the webApp directory. (But Only once; after re-copying it, I get the error message again.)
Also if I want to delete the file manually, by using Windows explorer, I get the error message that the file can't be deleted because it is used by Java(TM) Platform SE Binary.
So to delete the file (manually or via the bean) I have to wait for a restart of the application, which of course is not an acceptable solution for the end user.
I'm using JSF2.0 with Primefaces and Primefaces Mobile components. My IDE is Netbeans and I use Spring Webflow framework to navigate and trigger actions/methods between the xhtml pages.
Here's the code for the copying method in my JavaBean:
public void copyFotoToLocalhost() {
if (fotoList.size() > 0) {
for (int i = 0; i < fotoList.size(); i++) {
Foto tempPic = fotoList.get(i);
String tempItemName = tempPic.getItemName();
String originalFile = "D:\\localFilepath\\" + tempItemName;
String tempFileName = "D:\\WebAppPath\\src\\main\\webapp\\resources\\pics\\" + tempItemName;
File existTest = new File(tempFileName);
if (existTest.exists() == false) {
try {
File orFile = new File(originalFile);
File tempFile = new File(tempFileName);
InputStream in = new FileInputStream(orFile);
OutputStream out = new FileOutputStream(tempFile);
byte[] buf = new byte[8192];
int len;
while ((len = in.read(buf)) > 0) {
out.write(buf, 0, len);
}
in.close();
out.close();
tempFile.setWritable(true);
System.out.println("File copied.");
} catch (FileNotFoundException ex) {
System.out.println(ex.getMessage() + " in the specified directory.");
System.exit(0);
} catch (IOException e) {
System.out.println(e.getMessage());
}
}
}
}
}
Here's the code for the delete method:
public void deleteFotos() {
if (fotoList.size() > 0) {
for (int i = 0; i < fotoList.size(); i++) {
Foto tempPic = fotoList.get(i);
String tempItemName = tempPic.getItemName();
Path tempLocation = Paths.get("D:\\webAppPath\\src\\main\\webapp\\resources\\pics\\" + tempItemName);
fotoList.remove(i);
i--;
try {
Files.deleteIfExists(tempLocation);
System.out.println("sucessfully deleted" + tempPic.getItemName());
} catch (IOException ex) {
Logger.getLogger(WundDokuBean.class.getName()).log(Level.SEVERE, null, ex);
System.out.println("Fail # " + tempPic.getItemName());
}
}
fotoList.clear();
}
Do you have an idea, how to fix this?
I hope you understand my problem, if not please tell me which information you need, I'll try to provide it.

There is one xhtml page, where I want to show a picture, which is stored locally on my hard drive (for example: D:\pictures\test.jpg). Since browsers block images when they are located on a local harddrive (...)
I want to clear out a conceptual misunderstanding first: You seem to expect that it would work fine when the browser wouldn't have blocked it. This is completely untrue. You seem to expect that images are inlined in the HTML output. No, they are downloaded individually and independently from the HTML page. If you had continued to use local disk file system paths, then it would have worked only and only if your webpage visitor has also exactly the same file at exactly the same location at their disk file system. In reality, this is obviously not the case. It would only work if both the webbrowser and webserver runs at physically the same machine.
Coming back to your concrete problem of being unable to delete the file, it's is caused because the servletcontainer usually locks the files in expanded WAR folder. I can't tell the exact reason, but that's not relevant here as this whole approach is wrong anyway. This approach would fail when the deployed WAR file is not expanded on disk file system, but instead in server's memory. Also, hardcoding environment-specific disk file system paths is a bad idea. You'd need to edit, rewrite, recompile, rebuild the whole WAR everytime you change the environment. In other words, your webapp is not portable.
You need to keep the files there where they originally are and make them publicly available by a real URL. This can be achieved in 2 general ways:
Add a virtual host to the server config, pointing to D:\localFilepath\. How to achieve that depends on the server used. You didn't tell anything about the server make/version used, but using Spring suggests that you're not being able to use full Java EE stack and are likely using a barebones JSP/Servlet container such as Tomcat. In that case, it's a matter of adding the following line to its /conf/server.xml:
<Context docBase="D:\localFilepath" path="/fotos" />
This way they are available by http://localhost:8080/fotos/*.
Create a servlet which reads files from D:\localFilepath and writes to HTTP response. With Servlet 3.0 and Java 7 it's really a breeze. Here's a kickoff example (nullchecks/file-exist-checks/doHead()/caching/resuming omitted for brevity):
#WebServlet("/fotos/*")
public class FotosServlet extends HttpServlet {
#Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletExcpetion, IOException {
File file = new File("D:/localFilepath", request.getPathInfo().substring(1));
response.setHeader("Content-Type", getServletContext().getMimeType(file.getName()));
response.setHeader("Content-Length", String.valueOf(file.length()));
Files.copy(file.toPath(), response.getOutputStream());
}
}
That's basically it. This way they're available on http://localhost:8080/contextname/fotos/*.

writing temporary files in Tomcat

I need to create temporary directory but I'm always getting access denied when I try to create a file into the temporary directory.
java.io.FileNotFoundException: C:\tmpDir7504230706415790917 (Access Denied)
here's my code:
public static File createTempDir() throws IOException {
File temp = File.createTempFile("tmpDir", "", new File("C:/"));
temp.delete();
temp.mkdir();
return temp;
}
public File createFile(InputStream inputStream, File tmpDir ) {
File file = null;
if (tmpDir.isDirectory()) {
try {
file = new File(tmpDir.getAbsolutePath());
// write the inputStream to a FileOutputStream
OutputStream out = new FileOutputStream(file);
int read = 0;
byte[] bytes = new byte[1024];
while ((read = inputStream.read(bytes)) != -1) {
out.write(bytes, 0, read);
}
inputStream.close();
out.flush();
out.close();
System.out.println("New file created!");
} catch (IOException e) {
System.out.println(e.getMessage());
}
}
return file;
}
I'm working on a web application and I'm using tomcat. Is there a way to create temporary file on tomcat server memory? I know that's bizarre, but I don't know ... maybe it's possible.

You could use Tomcat's temp folder.
If you use
<%=System.getProperty("java.io.tmpdir")%>
in a JSP you can get path to it.

This line in your code says create a file whose name starts with text "tmpDir" in the directory "C:\". That is not what you want.
File temp = File.createTempFile("tmpDir","",new File("C:/"));
The operating system is properly disallowing that because C:\ is a protected directory. Use the following instead:
File temp = File.createTempFile("tmp",null);
This will let Java determine the appropriate temporary directory. Your file will have the simple prefix "tmp" followed by some random text. You can change "tmp" to anything meaningful for your app, in case you need to manually clean out these temp files and you want to be able to quickly identify them.

You usually cannot write onto C:\ directly due to the default permission setting. I sometime have permission issue for doing so. However, you can write your temporary file in your user folder. Usually, this is C:\Documents and Settings\UserName\ on XP or C:\Users\UserName\ on vista and Windows 7. A tool called SystemUtils from Apache Lang can be very useful if you want to get the home directory depending on OS platform.
For example:
SystemUtils.getUserDir();
SystemUtils.getUserHome();
Update
Also, you create a temp file object but you call mkdir to make it into a directory and try to write your file to that directory object. You can only write a file into a directory but not on the directory itself. To solve this problem, either don't call temp.mkdir(); or change this file=new File(tmpDir.getAbsolutePath()); to file=new File(tmpDir, "sometempname");

On Linux with tomcat7 installation:
So if you are running web application this is the temp directory Tomcat uses for the creation of temporary files.
TOMCAT_HOME/temp
In my case TOMCAT_HOME => /usr/share/tomcat7
If you are running Java program without tomcat, by default it uses /tmp directory.
Not sure if it affects but i ran this command too.
chmod 777 on TOMCAT_HOME/temp