public final class Configuration extends Object
A configuration encapsulates the readability graph that is the output of resolution. A readability graph is a directed graph whose vertices are of type ResolvedModule and the edges represent the readability amongst the modules. Configuration defines the modules() method to get the set of resolved modules in the graph.
ResolvedModule defines the reads() method to get the set of modules that a resolved module reads. The modules that are read may be in the same configuration or may be in parent configurations.
Configuration defines the resolve method to resolve a collection of root modules, and the resolveAndBind method to do resolution with service binding. There are instance and static variants of both methods. The instance methods create a configuration with the receiver as the parent configuration. The static methods are for more advanced cases where there can be more than one parent configuration.
Each layer of modules in the Java virtual machine is created from a configuration. The configuration for the boot layer is obtained by invoking
ModuleLayer.boot().configuration(). The configuration for the boot layer will often be the parent when creating new configurations.
The following example uses the resolve method to resolve a module named myapp with the configuration for the boot layer as the parent configuration. It prints the name of each resolved module and the names of the modules that each module reads.
Path dir1 = ..., dir2 = ..., dir3 = ...;
ModuleFinder finder = ModuleFinder.of(dir1, dir2, dir3);
Configuration parent = ModuleLayer.boot().configuration();
Configuration cf = parent.resolve(finder, ModuleFinder.of(), Set.of("myapp"));
cf.modules().forEach(m -> {
System.out.format("%s -> %s%n",
m.name(),
m.reads().stream()
.map(ResolvedModule::name)
.collect(Collectors.joining(", ")));
});
| Modifier and Type | Method | Description |
|---|---|---|
static Configuration |
empty() |
Returns the empty configuration. |
Optional |
findModule |
Finds a resolved module in this configuration, or if not in this configuration, the parent configurations. |
Set |
modules() |
Returns an unmodifiable set of the resolved modules in this configuration. |
List |
parents() |
Returns an unmodifiable list of this configuration's parents, in search order. |
Configuration |
resolve |
Resolves a collection of root modules, with this configuration as its parent, to create a new configuration. |
static Configuration |
resolve |
Resolves a collection of root modules to create a configuration. |
Configuration |
resolveAndBind |
Resolves a collection of root modules, with service binding, and with this configuration as its parent, to create a new configuration. |
static Configuration |
resolveAndBind |
Resolves a collection of root modules, with service binding, to create configuration. |
String |
toString() |
Returns a string describing this configuration. |
public Configuration resolve(ModuleFinder before, ModuleFinder after, Collection<String> roots)
resolve method when invoked with this configuration as the parent. In other words, if this configuration is cf then this method is equivalent to invoking:
Configuration.resolve(before, List.of(cf), after, roots);
before - The before module finder to find modulesafter - The after module finder to locate modules when not located by the before module finder or in parent configurationsroots - The possibly-empty collection of module names of the modules to resolveFindException - If resolution fails for any of the observability-related reasons specified by the static resolve methodResolutionException - If resolution fails any of the consistency checks specified by the static resolve methodSecurityException - If locating a module is denied by the security managerpublic Configuration resolveAndBind(ModuleFinder before, ModuleFinder after, Collection<String> roots)
resolveAndBind method when invoked with this configuration as the parent. In other words, if this configuration is cf then this method is equivalent to invoking:
Configuration.resolveAndBind(before, List.of(cf), after, roots);
before - The before module finder to find modulesafter - The after module finder to locate modules when not located by the before module finder or in parent configurationsroots - The possibly-empty collection of module names of the modules to resolveFindException - If resolution fails for any of the observability-related reasons specified by the static resolve methodResolutionException - If resolution fails any of the consistency checks specified by the static resolve methodSecurityException - If locating a module is denied by the security managerpublic static Configuration resolve(ModuleFinder before, List<Configuration> parents, ModuleFinder after, Collection<String> roots)
Each root module is located using the given before module finder. If a module is not found then it is located in the parent configuration as if by invoking the findModule method on each parent in iteration order. If not found then the module is located using the given after module finder. The same search order is used to locate transitive dependences. Root modules or dependences that are located in a parent configuration are resolved no further and are not included in the resulting configuration.
When all modules have been enumerated then a readability graph is computed, and in conjunction with the module exports and service use, checked for consistency.
Resolution may fail with FindException for the following observability-related reasons:
A root module, or a direct or transitive dependency, is not found.
An error occurs when attempting to find a module. Possible errors include I/O errors, errors detected parsing a module descriptor (module-info.class) or two versions of the same module are found in the same directory.
Resolution may fail with ResolutionException if any of the following consistency checks fail:
A cycle is detected, say where module m1 requires module m2 and m2 requires m1.
A module reads two or more modules with the same name. This includes the case where a module reads another with the same name as itself.
Two or more modules in the configuration export the same package to a module that reads both. This includes the case where a module M containing package p reads another module that exports p to M.
A module M declares that it "uses p.S" or "provides p.S with ..." but package p is neither in module M nor exported to M by any module that M reads.
before - The before module finder to find modulesparents - The list parent configurations in search orderafter - The after module finder to locate modules when not located by the before module finder or in parent configurationsroots - The possibly-empty collection of module names of the modules to resolveFindException - If resolution fails for any of observability-related reasons specified aboveResolutionException - If resolution fails for any of the consistency checks specified aboveIllegalArgumentException - If the list of parents is empty, or the list has two or more parents with modules for different target operating systems, architectures, or versionsSecurityException - If locating a module is denied by the security managerpublic static Configuration resolveAndBind(ModuleFinder before, List<Configuration> parents, ModuleFinder after, Collection<String> roots)
This method works exactly as specified by resolve except that the graph of resolved modules is augmented with modules induced by the service-use dependence relation.
More specifically, the root modules are resolved as if by calling resolve. The resolved modules, and all modules in the parent configurations, with service dependences are then examined. All modules found by the given module finders that provide an implementation of one or more of the service types are added to the module graph and then resolved as if by calling the
resolve method. Adding modules to the module graph may introduce new service-use dependences and so the process works iteratively until no more modules are added.
As service binding involves resolution then it may fail with
FindException or ResolutionException for exactly the same reasons specified in resolve.
before - The before module finder to find modulesparents - The list parent configurations in search orderafter - The after module finder to locate modules when not located by the before module finder or in parent configurationsroots - The possibly-empty collection of module names of the modules to resolveFindException - If resolution fails for any of the observability-related reasons specified by the static resolve methodResolutionException - If resolution fails any of the consistency checks specified by the static resolve methodIllegalArgumentException - If the list of parents is empty, or the list has two or more parents with modules for different target operating systems, architectures, or versionsSecurityException - If locating a module is denied by the security managerpublic static Configuration empty()
public List<Configuration> parents()
public Set<ResolvedModule> modules()
public Optional<ResolvedModule> findModule(String name)
findModule on each parent, in search order, until the module is found or all parents have been searched. In a tree of configurations then this is equivalent to a depth-first search.name - The module name of the resolved module to find
Optional if there isn't a module with this name in this configuration or any parent configurationspublic String toString()
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