Why does Eclipse find javax.swing but not Felix?

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In an ideal world, bundles would load all packages by importing them from other bundles (i.e. using the Import-Package header) or from their own private contents. However there is a security restriction in Java that states any class name starting with "java." must be loaded from the boot class loader. For example this includes java.lang.Object, java.lang.String, java.util.List etc. Therefore OSGi always delegates java.* class loading requests to the boot class loader.

All other packages should be imported with Import-Package if they are used by a bundle. This includes packages that are normally distributed with the JRE, such as javax.swing, javax.xml, org.w3c.com, org.ietf.jgss and so on. In order for those imports of JRE packages to be resolved, the System Bundle exports them; this is the case for all OSGi frameworks, including both Equinox (the framework normally used to run Eclipse) and Felix. The list of system bundle exports can be extended with the org.osgi.framework.system.packages.extra property.

However, there is an override mechanism called Boot Delegation, which makes all (or a subset) of packages automatically delegated to the boot class loader before attempting to load from imported packages or a bundle's own contents. Specifying org.osgi.framework.bootdelegation=* means that OSGi attempts to load all packages from the boot class loader. The list of packages can also be specified as a comma-separated list. Note that using this property is strongly discouraged because it leads to many class loading errors.

For historic reasons, Equinox runs with a boot delegation set to * when running as Eclipse. However, the out-of-the-box experience of "standalone" Equinox is that same as that of Felix, in which this is not set. So bundles running in Eclipse may gain access to javax.swing where a bundle running in either Equinox or Felix OSGi runtimes would not wire the dependencies up.

In summary: a bundle should always import the javax.swing package if it uses that package; then it will work correctly on any OSGi framework. It is bad practice to assume global visibility of any package other than those in the java.* namespace.

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