I'm using the Netbeans IDE, and I'm currently using a GlassFish server.
What I want to do is write to a file.
I looked at some pages, and the code I have now (that is not working as far as I know) looks like:
File outputFile = new File(getServletContext().getRealPath("/")
+ "TheFile.txt");
FileWriter fout = new FileWriter(outputFile);
fout.write("The Content");
fout.close();
This is my project's structure:
Also where will the file get placed?
Edit:
I forgot to mention there are some other folders below the ones in the picture: Test Packages, Libraries, Test Libraries and Configuration Files. However I don't think the file would get placed there.
Edit (newest):
I found out the file is stored in the /build/web folder, but this is not appearing in Netbeans. Even after I restarted it.
As you've coded, the file will be placed in public web root. That's where getRealPath("/") will point to. To be precise, it's the folder named Web Pages as in your screenshot. As an exercise, do the following to figure the absolute path, so that you can find it by OS disk explorer.
System.out.println(file.getAbsolutePath());
I don't do Netbeans, but likely you need to refresh the folder in your IDE after the write of the file so that it appears in the listing in the IDE. Click the folder and press F5. This is at least true for Eclipse.
That said, this approach is not recommended. This won't work when the servletcontainer isn't configured to expand the WAR on disk. Even when it did, you will lose all new files and changes in existing files when the WAR is been redeployed. It should not be used as a permanent storage. Rather store it on a fixed path outside the webapp or in a database (which is preferred since you seem want to reinvent a CMS).
Note that this is in no way guaranteed to work in all web containers or through restarts and will most likely be overwritten by a redeployment.
If you want to be able to allow your user to update content, you need to store the new content somewhere and have a servlet or a JSP-page or a facelet retrieve the new content from the backing storage and send it to the browser.
See the documentation for getRealPath. It returns you the location on the disk for something specified with a URL.
I'm guessing your file is in the root of your web application on the disk within Glassfish (where the WAR file is extracted). I don't know enough about Glassfish to say where that will be.
Also, note you are using string concatenation to create the file name, so if the getRealPath call doesn't return a String with a "/" on the end, then you might be creating a file in the parent directory of your web app. Perhaps best to use a File object for the parent directory when creating the File object for the actual file. Check out the File API.
I'd recommend creating the file outside of your web app. If you redeploy your WAR file then you might delete your file, which probably isn't what you want.
Being in a servlet makes little difference to the fact that you want to output a file. Just follow the standard file APIs as a starting point. Here's a tutorial.
Related
I searched around the web and here and couldn't find a conclusive answer to this rather simple question. I am using Java+MySQL+HTML and CSS.
I created a webapp, and in this webapp the user can upload the photos path to the database .At the same time I am creating a folder completely outside of tomcat to copy inserted images there. The folder is on my desktop as I am on localhost, but I want to make the storage on the server not on my desktop.
After checking stackoverflow I saw that it is bad to store photos/images in tomcats webapp/AppName folder because this will overwrite the images all the time at redeployment which I don't want to do.
My tomcat folder is on desktop. Can I create a folder to store the images for this specific app here:
\Desktop\ApacheTomcat\apache-tomcat-9.0.24\ ?
The folder would be called TripAppImages like \Desktop\ApacheTomcat\apache-tomcat-9.0.24\TripAppImages and will be besides all of tomcats other folders like bin, conf, etc. I will also use this folder to display the images that the user inserted , back to him in a html page.
EDIT: ok so I have finally come upon a message from here how to create a folder in tomcat webserver using java program? from BalusC which says:
"Please note that you shouldn't store the files in the expanded WAR folder, or they will get lost every time you redeploy the webapp. Store them on a fixed path outside Tomcat's /webapps folder."
This I believe means that I can store the images like this \Desktop\ApacheTomcat\apache-tomcat-9.0.24\TripAppImages. As long ass they are not in the webapp folder it means they won't be overwritten.
The only folders you should avoid are temp, webapp, work and its subfolders, because yes, those folders can have its content replaced or deleted during deploys and cleanings, every other folder inside tomcat can be considered as 'just a folder' that, if you don't modify its contents, you can use the way you want. Of course it would not be normal or standard to, for example, store videos inside Tomcat\bin but if you don't touch the original files there you can do it.
So technically speaking, you can create a folder like \Desktop\ApacheTomcat\apache-tomcat-9.0.24\icecream and put images there it will not be erased or replaced by a deploy.
If it is just for you, temporary or not production, just avoid the three folders mentioned at the beginning and you are good to go.
If I have a resource file (mydata.txt) in resources folder (set up as another source folder) of my application. This mydata.txt eventually would be packaged inside root of a jar file (.war) to be deployed to some application server (Tomcat, Jetty, WildFly).
File mydata.txt has some crucial data needed to the application, and this file shall be appended by the application.
To get a file from jar I can use getClass().getResourceAsStream("/mydata.txt") - thus I get this file as InputStream. But there is no way I can get this file as OutputStream and write to it.
All solutions with getClass().getResource() - returning URL are discouraged, getResourceAsStream is always recommended, but it allows only reading, not writing/updating/appending the file.
getClass().getProtectionDomain().getCodeSource() solution is also discouraged to get (write) access to the file.
I could create some file in a temporary directory on Tomcat Server (System.getProperty("java.io.tmpdir") and write to it, but it is nonsense because this file contents is crucial for the application (to write it to tmp dir), besides I need to append file, not create a new one and write to it.
Also, I am not sure that writing to any other directory (other than tmp) of application server is a good idea (please correct me if I am wrong here).
So I come to the conclusion that it is not recommended to save any data to a file in enterprise application, so I shall always use a database instead?
In short: Yes. Beside all you mentioned (which is all correct) the biggest problems are
concurrent access
transaction handling
which both a database serves perfect and with a file approach is just a pain in the ****
In addition to that especially an application server provides you with configuration of connection (and pools) to data sources of any kind, which is really handy in a production environment.
I need to write a little Grails (or Java) app that will handle authentication (from our proprietary Single Sign On system) and then once authenticated allow a user to download files. This is very straight forward if I simply include the files in the WAR file of the application, however, I'd like to avoid that since there will be multiple files and I'd rather not have to upload a new WAR file every time we add a new file. Is it possible to accomplish this by having the application be in a WAR file but the files outside the WAR file, if so, how do I configure this kind of setup? We'll be running this on Tomcat.
Yes this is possible. Without knowing all your requirements or what you have tried and why it didn't work work for you the best I can do is give you a general idea of how to accomplish this.
Have a controller that takes an ID of the file that you want the user to download. Based on this key find the associated Domain instance. The domain should store the file name of the file. Then use this file name to resolve the file from the local file system (path configured in your application configuration). Open the file and stream the contents to the browser. Be sure to set he headers correctly to indicate the file name and size.
There are a lot of moving parts involved here but it can be done. Now, if you get stuck on something I suggest you post what you have tried and what's not working about it. Otherwise, the best we/I can do is give you general guidance/advice.
Hope this helps!
Edit
The real key is going to be in the controller for downloading the files. Here is a quick snippet of what that may look like:
String fileName = "something.zip" // should come from your domain instance
String filePathAndName = "/downloads/${fileName}" // should come from your configuration
response.setContentType("application/octet-stream")
response.setHeader("Content-disposition", "attachment;filename=${fileName")
// this will actually buffer/stream the file in 8k chunks instead of reading the entire file into memory.
org.apache.commons.io.IOUtils.copy((new File(filePathAndName)).openStream(), response.outputStream)
response.outputStream.flush()
response.outputStream.close()
As i know it returns the application path? But what exactly the use of it.
In many environments the application user is not allowed to read any files outside of the deployment directory. This is mostly done for security purposes - for example if someone hacks your application they won't be able to read a passwords file.
And in professionally managed environments developers often don't have a say in which directory the application will be placed.
So if you need to read a file like properties, images, certificates, etc. you can place it in the application directory (or .war file) and use getRealPath("") to get the path you need to load.
As an alternative you can place the external files on the classpath but there are sometimes issues with this. For large files most app servers will try to load the entire file into memory and cache it if it is on the classpath.
The getRealPath() gives the absolute path (on the file system) leading to a file specified in the parameters of the call. It returns the path in the format specific to the OS.
The getContextPath() on the other hand returns the URI or the relative path to the resource.
As far as I remember, I've used it to save images or other data files, since it allows you to see where your application is deployed at the moment. For example, Eclipse and Tomcat will create a temporary folder that's buried deep somewhere within your Eclipse profile and deploy the app there.
This is a real path in file system.
From javadoc:
The real path returned will be in a form appropriate to the computer and operating system on which the servlet container is running, including the proper path separators. This method returns null if the servlet container cannot translate the virtual path to a real path for any reason (such as when the content is being made available from a .war archive).
I think it is very clear. Why do we need this? Sometimes web applications perform some manipulation in file system. For example read stuff from files, write files etc. This API allows you to access the place where your JSPs and other stuff is really stored.
I am doing a project in java and in that i need to add and modify my
text file at runtime,which is grouped in the jar.
I am using class.getResourceAsStream(filename) this method we
can read that file from class path.
i want to write into the same textfile.
What is the possible solution for this.
If i can't update the text file in jar what other solution is there?
Appreciate any help.
The easiest solution here is to not put the file in the jar. It sounds like you are putting files in your jar so that your user only needs to worry about one file that contains everything related to that program. This is an artificial constraint and just add headaches.
There is a simple solution that still allows you to distribute just the jar file. At start up, attempt to read the file from the file system. If you don't find it, use default values that are encoded in you program. Then when changes are made, you can write it to the file system.
In general, you can't update a file that you located using getResourceAsStream. It might be a file in a JAR/ZIP file ... and writing it would entail rewriting the entire JAR file. It might be a remote file served up by a Url classloader.
For your sanity (and good practice), you should not attempt to update files that you access via the classpath. If you need to, read the file out of the JAR file (or whatever), copy it into the regular file system, and then update the copy.
I'm not saying that it is impossible to do this in all cases. Indeed, in most normal cases you can do it with some effort. However, this is not supported, and there are no standard APIs for doing this.
Furthermore, attempts to update resources are liable to cause anomalies in the classloader. For example, I'd expect resources in JAR files to not update (from the perspective of the application) until the application restarted. But resources in exploded JAR files probably would update ... though new resources might not show up.
Finally, there are cases where updating a resource is impossible:
When the user doesn't have write access to the application's installation directory. This is typical for a properly administered UNIX / Linux machine.
When the JAR file is fetched from a remote server, you are likely not to be able to write the updates back.
When you are using an arbitrary custom classloader, you've got no way of knowing where the actual bytes of an updated resource should be stored, and no way of storing them.
All JAR rewriting techniques in Java look similar. Open the Jar file, read all of it's contents, and write a new Jar file containing the unmodified contents (and the modifications you whished to make). Such techniques are not advisable for a Jar file on the class path, much less a Jar file you're running from.
If you decide you must do it this way, Java World has a few articles:
Modifying Archives, Part 1
Modifying Archives, Part 2
A good solution that avoids the need to put your items into a Jar file is to read (if present) a properties file out of a hidden subdirectory in the user's home directory. The logic looks a bit like this:
if (the hidden directory named after my application doesn't exist) {
makeTheHiddenDirectory();
writeTheDefaultPropertiesFile();
}
Properties appProps = new Properties();
appProps.load(new FileInputStream(fileInHiddenDir));
...
... After the appProps have changed ...
...
appProps.store(new FileOutputStream(fileInHiddenDir), "Do not modify this file");
Look to java.util.Properties, and keep in mind that they have two different load and store formats (key = value based and XML based). Pick the one that suits you best.
If i can't update the text file in jar what other solution is there?
Store the information in any of:
Cookies
The server
Deploy the applet using 1.6.0_10+, launch it using JWS and use the PersistenceService to store the information. Here is my demo. of the PersistenceService.
Also, if your users will agree to a trusted applet (which seems overkill for this), you might write the information to a sub-directory of user.home.