Module java.base

Package java.util.spi

Interface ToolProvider

public interface ToolProvider

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 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

Method Summary

Modifier and Type	Method	Description
default Optional<String>	description()	Returns a short description of the tool, or an empty Optional if no description is available.
static Optional<ToolProvider>	findFirst(String name)	Returns the first instance of a ToolProvider with the given name, as loaded by ServiceLoader using the system class loader.
String	name()	Returns the name of this tool provider.
default int	run(PrintStream out, PrintStream err, String... args)	Runs an instance of the tool, returning zero for a successful run.
int	run(PrintWriter out, PrintWriter err, String... args)	Runs an instance of the tool, returning zero for a successful run.

Method Details

name

String name()

Returns the name of this tool provider.

API Note:

It is recommended that the name be the same as would be used on the command line: for example, "javac", "jar", "jlink".

Returns:

the name of this tool provider

description

default Optional<String> description()

Returns a short description of the tool, or an empty Optional if no description is available.

API Note:

It is recommended that the description fits into a single line in order to allow creating concise overviews like the following:

 jar
   Create, manipulate, and extract an archive of classes and resources.
 javac
   Read Java declarations and compile them into class files.
 jlink
   Assemble a set of modules (...) into a custom runtime image.
 
 

Implementation Requirements:

This implementation returns an empty Optional.

Returns:

a short description of the tool, or an empty Optional if no description is available

Since:

19

run

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.

API Note:

The interpretation of the arguments will be specific to each tool.

Parameters:

out - a stream to which "expected" output should be written

err - a stream to which any error messages should be written

args - the command-line arguments for the tool

Returns:

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 null, or if there are any null values in the args array

run

default int run(PrintStream out,
 PrintStream 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.

API Note:

The interpretation of the arguments will be specific to each tool.

Implementation Note:

This implementation wraps the out and err streams within PrintWriters, and then calls run(PrintWriter, PrintWriter, String[]).

Parameters:

out - a stream to which "expected" output should be written

err - a stream to which any error messages should be written

args - the command-line arguments for the tool

Returns:

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 null, or if there are any null values in the args array

findFirst

static Optional<ToolProvider> findFirst(String name)

Returns the first instance of a ToolProvider with the given name, as loaded by ServiceLoader using the system class loader.

Parameters:

name - the name of the desired tool provider

Returns:

an Optional<ToolProvider> of the first instance found

Throws:

NullPointerException - if name is null