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package java.util.spi;
import java.io.PrintStream;
import java.io.PrintWriter;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Objects;
import java.util.Optional;
import java.util.ServiceLoader;
import java.util.stream.StreamSupport;
/**
* An interface for command-line tools to provide a way to
* be invoked without necessarily starting a new VM.
*
* Tool providers are normally located using the service-provider
* loading facility defined by {@link ServiceLoader}.
* Each provider must provide a name, and a method to run
* an instance of the corresponding tool. When a tool is run,
* it will be provided with an array of string arguments, and a
* pair of streams: one for normal (or expected) output and the other
* for reporting any errors that may occur.
* The interpretation of the string arguments will normally be defined by
* each individual tool provider, but will generally correspond to the
* arguments that could be provided to the tool when invoking the tool
* from the command line.
*
* @since 9
*/
public interface ToolProvider {
/**
* Returns the name of this tool provider.
*
* @apiNote It is recommended that the name be the same as would be
* used on the command line: for example, "javac", "jar", "jlink".
*
* @return the name of this tool provider
*/
String name();
/**
* Runs an instance of the tool, returning zero for a successful run.
* Any non-zero return value indicates a tool-specific error during the
* execution.
*
* Two streams should be provided, for "expected" output, and for any
* error messages. If it is not necessary to distinguish the output,
* the same stream may be used for both.
*
* @apiNote The interpretation of the arguments will be specific to
* each tool.
*
* @param out a stream to which "expected" output should be written
*
* @param err a stream to which any error messages should be written
*
* @param args the command-line arguments for the tool
*
* @return the result of executing the tool.
* A return value of 0 means the tool did not encounter any errors;
* any other value indicates that at least one error occurred
* during execution.
*
* @throws NullPointerException if any of the arguments are {@code null},
* or if there are any {@code null} values in the {@code args}
* array
*/
int run(PrintWriter out, PrintWriter err, String... args);
/**
* Runs an instance of the tool, returning zero for a successful run.
* Any non-zero return value indicates a tool-specific error during the
* execution.
*
* Two streams should be provided, for "expected" output, and for any
* error messages. If it is not necessary to distinguish the output,
* the same stream may be used for both.
*
* @apiNote The interpretation of the arguments will be specific to
* each tool.
*
* @implNote This implementation wraps the {@code out} and {@code err}
* streams within {@link PrintWriter}s, and then calls
* {@link #run(PrintWriter, PrintWriter, String[])}.
*
* @param out a stream to which "expected" output should be written
*
* @param err a stream to which any error messages should be written
*
* @param args the command-line arguments for the tool
*
* @return the result of executing the tool.
* A return value of 0 means the tool did not encounter any errors;
* any other value indicates that at least one error occurred
* during execution.
*
* @throws NullPointerException if any of the arguments are {@code null},
* or if there are any {@code null} values in the {@code args}
* array
*/
default int run(PrintStream out, PrintStream err, String... args) {
Objects.requireNonNull(out);
Objects.requireNonNull(err);
Objects.requireNonNull(args);
for (String arg : args) {
Objects.requireNonNull(arg);
}
PrintWriter outWriter = new PrintWriter(out);
PrintWriter errWriter = new PrintWriter(err);
try {
try {
return run(outWriter, errWriter, args);
} finally {
outWriter.flush();
}
} finally {
errWriter.flush();
}
}
/**
* Returns the first instance of a {@code ToolProvider} with the given name,
* as loaded by {@link ServiceLoader} using the system class loader.
*
* @param name the name of the desired tool provider
*
* @return an {@code Optional} of the first instance found
*
* @throws NullPointerException if {@code name} is {@code null}
*/
@SuppressWarnings("removal")
static Optional findFirst(String name) {
Objects.requireNonNull(name);
ClassLoader systemClassLoader = ClassLoader.getSystemClassLoader();
return AccessController.doPrivileged(
(PrivilegedAction>) () -> {
ServiceLoader sl =
ServiceLoader.load(ToolProvider.class, systemClassLoader);
return StreamSupport.stream(sl.spliterator(), false)
.filter(p -> p.name().equals(name))
.findFirst();
});
}
}