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The META-INF directory

• MANIFEST.MF

• INDEX.LIST

• x.SF

• x.DSA

• services/

Service Provider

Overview

A service is represented by an abstract class. A provider of a given service contains one or more concrete classes that extend this service class with data and code specific to the provider. This provider class will typically not be the entire provider itself but rather a proxy that contains enough information to decide whether the provider is able to satisfy a particular request together with code that can create the actual provider on demand. The details of provider classes tend to be highly service-specific; no single class or interface could possibly unify them, so no such class has been defined. The only requirement enforced here is that provider classes must have a zero-argument constructor so that they may be instantiated during lookup.
 

Provider-Configuration File

Example

    public abstract CharEncoder getEncoder(String encodingName);
  public abstract CharDecoder getDecoder(String encodingName);

Each method returns an appropriate object or null if it cannot translate the given encoding. Typical CharCodec providers will support more than one encoding.

If sun.io.StandardCodec is a provider of the CharCodec service then its jar file would contain the file META-INF/services/java.io.spi.CharCodec. This file would contain the single line:

   sun.io.StandardCodec    # Standard codecs for the platform

To locate an encoder for a given encoding name, the internal I/O code would do something like this:

   CharEncoder getEncoder(String encodingName) {
       Iterator ps = Service.providers(CharCodec.class);
       while (ps.hasNext()) {
           CharCodec cc = (CharCodec)ps.next();
           CharEncoder ce = cc.getEncoder(encodingName);
           if (ce != null)
               return ce;
       }
       return null;
   }
 

The provider-lookup mechanism always executes in the security context of the caller. Trusted system code should typically invoke the methods in this class from within a privileged security context.