There are many places in my code in which temporary files are deleted and in some cases these temp files are not deleted.
Is there a way to find in Java where files were created but not deleted (similar to finding memory leaks in C++)?
By overriding the File class you can add the opened file into a set and remove it when you delete it. That way you should be able to probe which files are opened any given Point. Not sure that's what you are looking for though.
It's not a "pretty" solution, but you could use a custom SecurityManager and look for FilePermission.
private static class FileSecurityManager extends SecurityManager {
#Override
public void checkPermission(Permission perm) {
if (perm instanceof FilePermission) {
System.out.println(perm);
}
// super.checkPermission(perm);
}
}
public static void main(String[] args) throws Exception {
System.setSecurityManager(new FileSecurityManager());
Files.delete(Files.createTempFile(null, null));
File.createTempFile("tempfile", null).delete();
}
This example works with standard IO and NIO access to the filesystem.
Related
I'm trying to rename an existing file using File#renameTo(), but it doesn't seem to work.
The following code represents what I am trying to do:
public class RenameFileDirectory {
public static void main(String[] args) throws IOException {
new RenameFileDirectory();
}
public RenameFileDirectory() throws IOException {
File file = new File("C:\\Users\\User-PC\\Desktop\\Nouveau dossier2\\file.png");
File desFile = new File ("C:\\Users\\User-PC\\Desktop\\Nouveau dossier2\\file2.png");
if (file.renameTo(desFile)) {
System.out.println("successful rename");
} else {
System.out.println("error");
}
}
}
Try using Files.move instead. If you read the javadocs for renameTo, it states that:
Many aspects of the behavior of this method are inherently platform-dependent: The rename operation might not be able to move a file from one filesystem to another, it might not be atomic, and it might not succeed if a file with the destination abstract pathname already exists. The return value should always be checked to make sure that the rename operation was successful.
I have a simple plugin system, that loads external JAR plugins into main application. I am using Mountainblade Modular to do so. Not sure how they do it "under the hood" but probably it's something standard.
This works fine, I instantiate classes from external jar and it all works. Except that some plugins come with icons/images. I am a bit unsure on how do I load/refer to images from that external JAR (with code inside that external JAR, as it is ran in context of the main JAR, kind of)
How should I approach this?
This issue is not as straightforward as it seems to be.
When you load classes from external jar, they are "loaded" into JVM. By "loading" into JVM I mean that JVM is responsible for their storage in memory. Usually it is done like this:
ClassLoader myClassLoader = new MyClassLoader(jarFileContent);
Class myExtClass = myClassLoader.loadClass(myClassName);
Resources from classpath jars can be accessed easily with
InputStream resourceStream = myClass.getResourceAsStream("/myFile.txt");
You can do that, because these jars are in classpath, I mean their location is known. These files are not stored in memory. When resource is accessed, JVM can search for it in classpath jars (for example on file system).
But for external jars it is completely different: jar comes from nowhere, is once processed and forgotten. JVM does not load resources from it in memory. In order to access these files, you have to manually organize their storage. I've done this once so I can share the code. It will help you to understand the basic idea (but probably won't help you with your specific library).
// Method from custom UrlClassLoader class.
// jarContent here is byte array of loaded jar file.
// important notes:
// resources can be accesed only with this custom class loader
// resource content is provided with the help of custom URLStreamHandler
#Override
protected URL findResource(String name) {
JarInputStream jarInputStream;
try {
jarInputStream = new JarInputStream(new ByteArrayInputStream(jarContent));
JarEntry jarEntry;
while (true) {
jarEntry = jarInputStream.getNextJarEntry();
if (jarEntry == null) {
break;
}
if (name.equals(jarEntry.getName())) {
final byte[] bytes = IOUtils.toByteArray(jarInputStream);
return new URL(null, "in-memory-bytes", new URLStreamHandler() {
#Override
protected URLConnection openConnection(URL u) throws IOException {
return new URLConnection(u) {
#Override
public void connect() throws IOException {
// nothing to do here
}
#Override
public InputStream getInputStream() throws IOException {
return new ByteArrayInputStream(bytes);
}
};
}
});
}
}
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
I have seen many class loader questions, but still was not able to figure why, the error here.
I am writing a program which uses 2 versions of jars. One is needed to get content from older storage, and another to store content in new storage.
Since, I need either of the jar to be loaded at a time, I used JarClassLoader to create a proxy for adding one jar and loading its classes. But I face ClassNotFoundException.
public class HbaseMigrator implements Runnable {
public void run() {
JarClassLoader jcl = new JarClassLoader();
jcl.add("hadoop-0.13.0-core-modified-1.jar");
Object obj1 = JclObjectFactory.getInstance().create(jcl, "UserMigThreadImpl", toProcessQueue,threadName, latch,DBUtil,lock);
MigThread mig = JclUtils.cast(obj1, MigThread.class, jcl);
Thread.currentThread().setContextClassLoader(jcl);
try {
Method method = MigThread.class.getMethod("callthis", new Class[]{});
method.invoke(mig, new Object[]{});
// mig.callthis();
} catch( Exception e) {
e.printStackTrace();
} catch(Error er) {
er.printStackTrace();
}
}
}
Method called is:
public void callthis() {
DFSUtil = new DFSAccessAPIImpl();
.........
}
This class instantiation internally uses hadoop modified jar, which is not picked up from my classloader and it throws ClassNotFoundException.
What is that I am doing wrong ?
JarClassLoader used here is jcloader :
org.xeustechnologies.jcl.JarClassLoader
I experienced this problem with loading plugins to my application, so I decided to try to load all .class files from all jars in path. Maybe this code snipped from my app will help you.
https://bitbucket.org/rsohlich/plagdetector/src/432b52f252ff7647221b7e91b08731bd9cbe2a70/PlagDetectorSpring/src/main/java/cz/sohlich/app/service/impl/PluginHolderImpl.java
I'm using JarFile and JarURLConnection to load files out of a jar file. I'm then taking the classes, and loading them via BCEL (ByteCode Engineering Library, apache library). I cant just directly use a class loader because im modifying some classes slightly with the BCEL. I need to load the classes by their bytes into my bcel loader. However, one of the classes I'm loading references a resource. This resource is inside of the jar, so I can get the file (When iterating over the entries in the JarFile, I ignore the regular files, and take the class files for loading later). But just having the file won't do me any good, as the class loads it as a resource. Is there any way I can take that resource from the jar (well I can take it and load it into a byte[], the next part is the issue) and dynamically add it as a resource for my program, so that the classes that I load wont be missing their resources?
Got a lot of stuff here, if anythings confusing, ask in comments, I might've said something wrong, or missed something altogether :) Thanks
I'll show a little of my class loader here (extends ClassLoader):
#Override
public URL getResource(String name) {
System.out.println("LOADING RESOURCE: " + name);
try {
return new URL(null, name, new Handler(files));
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
Now, it is printing out "LOADING RESOURCE: filename", but its then giving me a MalformedURLException (I have no protocol atm, just a file path, that's not a true valid path, but it's just an attempt to give it to my Handler class below).
class Handler extends URLStreamHandler {
#Override
protected URLConnection openConnection(URL u) throws IOException {
return new URLConnection(u) {
#Override
public void connect() throws IOException {
}
#Override
public InputStream getInputStream() throws IOException {
System.out.println("IS: " + url);
return /*method to get input steam*/;
}
};
}
}
The /*method to get input steam*/ is set in my real code, but that's not relevant here. So any further ideas with this?
I have two programs: one CLI program, and one GUI. The GUI is a frontend for the CLI, but also a GUI for another program as well.
I am importing the CLI's classes and extending them in the GUI to add GUI elements to the classes, and all is great.
But now I want to split the CLI that I currently have embedded in the GUI (as an included JAR). The JAR is in a fixed location (/opt/program/prog.jar), and the application will only be used on Linux, so I realize that this breaks traditional Java thought.
I've edited the ClassPath in the Manifest file to reflect this change, and it works fine. However, when I remove the file, the GUI fails to load, citing not being able to load the class.
Is there a way to try to load a class and if it does not work, then do something else? In essence, I'm trying to catch the ClassNotFound exception, but have not had any luck yet.
One common way to check for class existence is to just do a Class.forName("my.Class"). You can wrap that with a try/catch that catches ClassNotFoundException and decide what to do. If you want, you could do that in a wrapper class that has a main(). You could try to load the class and if it succeeds, then call main() on the loaded class and if not, do something else.
public static void main(String arg[]) {
try {
Class.forName("my.OtherMain");
// worked, call it
OtherMain.main();
} catch(ClassNotFoundException e) {
// fallback to some other behavior
doOtherThing();
}
}
Is there a way to try to load a class and if it does not work, then do something else?
Assuming you had a class file in C:\ called Foo.class
public static void main(String[] args) {
File f = new File("c:\\");
if (f.exists()) {
URLClassLoader CLoader;
try {
CLoader = new URLClassLoader(new URL[]{f.toURL()});
Class loadedClass = CLoader.loadClass("Foo");
} catch (ClassNotFoundException ex) {
} catch (MalformedURLException ex) {
}
} else {
//do something else...
}
}