How can resource of a bundle be shared with other bundle(but not just one)?
For example I don't want to duplicate the images or properties file to all bundles, instead I want to access them from a single place.
I tried to use Fragment-Host, but there is not possible to specify multiple bundles(at least I do not know how)
eg:
<!-rest of the pom-->
<instructions>
<Fragment-Host>
com.bundlehost
</Fragment-Host>
</instructions>
As Dmytro notes, you can use OSGi API methods to access the resources in any bundle. However the harder question is this: how do you know from which bundle to access these resources, and how do you know where they are located within the bundle?
If you just make assumptions or hard-code the answer, then you end up with a very brittle system and a hidden coupling between the bundles. Then when somebody deploys your bundles into an application but doesn't include the resource bundle, everything breaks. This defeats the point of modularity.
You can use Bundle.getEntryPaths() and Bundle.getEntry() to get bundle resources. To read content use URL.openStream()
You can also use normal package imports and exports to ensure the resources are on the class path of the consuming bundle. See, for example, access common property file inside bundle with osgi.
Related
I'm creating a Liferay 7.1 OSGi bundle, which has some external dependencies in it. In consideration of time, we opted to embed the external JAR in our OSGi Bundle. I've managed to create a bnd file, which includes all of the ElasticSearch dependencies, and put them on the bundle classpath. I've used the source-code from github (https://github.com/liferay/liferay-portal/blob/master/modules/apps/portal-search-elasticsearch6/portal-search-elasticsearch6-impl/build.gradle) and the bnd.bnd file, to check what's imported.
When activating the bundle, an exception is thrown:
The activate method has thrown an exception
java.util.ServiceConfigurationError: org.elasticsearch.common.xcontent.XContentBuilderExtension: Provider org.elasticsearch.common.xcontent.XContentElasticsearchExtension not a subtype
at java.util.ServiceLoader.fail(ServiceLoader.java:239)
at java.util.ServiceLoader.access$300(ServiceLoader.java:185)
at java.util.ServiceLoader$LazyIterator.nextService(ServiceLoader.java:376)
at java.util.ServiceLoader$LazyIterator.next(ServiceLoader.java:404)
at java.util.ServiceLoader$1.next(ServiceLoader.java:480)
at org.elasticsearch.common.xcontent.XContentBuilder.<clinit>(XContentBuilder.java:118)
at org.elasticsearch.common.settings.Setting.arrayToParsableString(Setting.java:1257)
The XContentBuilderExtension is from the elasticsearch-x-content-6.5.0.jar,
the XContentElasticsearchExtension class, is included in the elasticsearch-6.5.0.jar. Both are Included Resources, and have been put on the classpath.
The Activate-method initializes a TransportClient in my other jar, hence it happens on activation ;).
Edit:
I've noticed that this error does NOT occur when installing this the first time, or when the portal restarts. So it only occurs when I uninstall and reinstall the bundle. (This is functionality I really prefer to have!). Maybe a stupid thought.. But could it be that there is some 'hanging thread'? That the bundle is not correctly installed, or that the TransportClient still is alive? I'm checking this out. Any hints are welcome!
Edit 2:
I'm fearing this is an incompatibility between SPI and OSGi? I've checked: The High Level Rest Client has the same issue. (But then with another Extension). I'm going to try the Low-Level Rest Client. This should work, as there are minimal dependencies, I'm guessing. I'm still very curious on why the incompatibility is there. I'm certainly no expert on OSGi, neither on SPI. (Time to learn new stuff!)
Seems like a case where OSGi uses your bundle to solve a dependency from another bundle, probably one that used your bundle to solve a package when the system started.
Looking at the symptoms: it does not occur when booting or restarts. Also it is not a subtype.
When OSGi uses that bundle to solve a dependency, it will keep a copy around, even when you remove it. When the bundle comes back a package that was previously used by another bundle may still be around and you can have the situation where a class used has two version of itself, from different classloaders, meaning they are not the same class and therefore, not a subtype.
Expose only the necessary to minimize the effects of this. Import only if needs importing. If you are using Liferay Gradle configuration to include the bundle inside, stop - it's a terrible way to include as it exposes a lot. If using the bnd file to include a resource and create an entry for the adicional classpath location, do not expose if not necessary. If you have several bundles using one as dependency, make sure about the version they use and if the exchange objects from the problematic class, if they do, than extra care is required.
PS: you can include attributes when exporting and/or importing in order to be more specific and avoid using packages from the wrong origin.
You can have 2 elastic search connections inside one Java app and Liferay is by default not exposing the connection that it holds.
A way around it is to rebuild the Liferay ES connector. It's not a big deal because you don't need to change the code only the OSGi descriptor to expose more services.
I did it in one POC project and worked fine. The tricky thing is to rebuild the Liferay jar but that was explained by Pettry by his google like search blog posts. https://community.liferay.com/blogs/-/blogs/creating-a-google-like-search (it is a series but it's kind of hard to navigate in the new Liferay blogs but Google will probably help) Either way it is all nicely documented here https://github.com/peerkar/liferay-gsearch
the only thing then what needs to be done is to add org.elasticsearch.* in the bnd.bnd file in the export section. You will then be able to work with the native elastic API.
I have two OSGi bundles A and B. Both are created with the API/implementation model. Both the bundles are activated through Blueprint mechanism. Both the API bundles export the interfaces whereas the implementation bundles don't export anything. Only A has dependency on B.
My issue is, I want to pass a resource file name (xml file) that resides in bundle A to Bundle B (after I get hold of B using the BundleContext.getServiceReferences() method) and then load the resource in Bundle B and process it. How can I achieve the same and is it even doable?
I read the following post and Neil Bartlett's answer suggest it should work.
Access resources in another osgi bundle?
However, when I read about getEntry, findEntries, getEntrypath methods, they don't talk about other bundles (or I misunderstood it). They talk only about fragments.
My question is, can I achieve what I am looking for using any of the above three methods? If so, can you please point to some other thread that has the answers or some sample code?
If this is not possible, can I use fragment bundles(containing only resources)? Again Bundle B is more like a provider where it can take any resource file and process it and satisfy clients requests (Bundle A). So even if I want to use bundle fragment approach, I need B to load the fragment bundle (only on needed basis) specified by clients (say they give the fragment bundle symbolic name). Please provide suggestions or other posts related to similar issues or any samples.
The easiest way to access a resource in a bundle is to use the classLoader of the bundle. In bundle A you get service MyService and do:
InputStream is = this.getClass().getResourceAsStream("myresource.xml");
MyService service.doSomething(is);
or if you prefer a URL:
URL url = this.getClass().getResource("myresource.xml");
MyService service.doSomething(url);
This works as we already resolve the resource before making the call. If you want to give the service just a relative path then you additionally need to give it the classLoader to get the resource from.
ClassLoader bundleALoader = this.getClass().getClassLoader();
MyService service.doSomething(bundleALoader, "myresource.xml");
Keep in mind though that this.getResource() will lookup the resource relatively to the package of "this" while classLoder.getResource() will lookup from the top of the name space.
Btw. These concepts also work fine outside of OSGi. The difference is only that in OSGi you have to make sure to use the classLoader that has visibility of a resource while outside there is often only one classLoader that sees all resources.
For publishing with SSL using the Endpoint I need to access classes under the packages com.sun.net.httpserver.*
Using the Eclipse IDE I found a way to use this classes. But exporting the bundles and running them in another equinox OSGi Installation I can't start the bundle throwing the following error:
java.lang.NoClassDefFoundError: com/sun/net/httpserver/HttpsConfigurator
Anyone an Idea how to solve this issue?
Thanks!
The package you're referring to is part of the JDK. You need to expose it, to make it available in OSGi and you have two options:
The first, and in most cases preferred option, is to expose this package through the system bundle. The OSGi framework has a property that you can set to do this:
org.osgi.framework.system.packages.extra=...
As its value, you provide it with a comma separated list of packages that you want to expose, on top of the ones that are already exposed by the framework. In your case, at least com.sun.net.httpserver, but there might be more packages that you need. In this case, also make sure that the bundle that uses this package imports this package.
The second option is to use a mechanism used boot delegation. It should only be used as a last resort, as it breaks modularity and if it's not used carefully it might lead to other problems. Again, this is a property that you need to set:
org.osgi.framework.bootdelegation=*
Here, you can provide a comma separated list of packages that should be loaded by the boot class loader. Wildcards are supported (as seen in the example above) but you are encouraged to be as specific as possible, so in your case for example use com.sun.* as the value.
osgi (equinox 3.6) framework while loading bundle creates bundle meta files in specified bundle directory . we are working on spawning multiple jvm's . Can we use bundle folder where my previous jvm has created ? I meant can we install all bundles once and use them for many applications?
It's a bit difficult to work out what you're asking... but it sounds like you want to share the OSGi storage directory between multiple separate OSGi frameworks running in different JVMs. This is not possible.
a) Yes you can share the same location URL among frameworks
b) You cannot share the framework bundle storage area/bundle cache (org.osgi.framework.storage property)
You know there is a special reference: schema for OSGi frameworks? This allows you to install frameworks quicker. Just prefix a URL with reference: scheme.
reference:file://....
Can i use a service in the class file which is generated using javaassist. how can i achieve that?? and as this class is created dynamically how can i register that this class is using the provided service of another class?
I've asked a similar question here.
The smallest unit of 'installation' would be a bundle. You could generate a sort of 'virtual bundle' around your class file, including a OSGI-INF/componentX.xml descriptor, and install that into OSGi.
If it changes, regenerate the bundle and update OSGi.
I didn't go down this path as I have a lot of generated code (about 4500 different scripts that all have dependencies) and I fear that I'd get into problems if I'd generate that many bundles.
I also got a tip about the Felix Dependency manager, but I haven't thoroughly checked that out yet, it might do the things we need.