Introduction to the technical principles of the Picocli framework in the Java class library
Introduction to the technical principles of the Picocli framework in the Java class library
Overview:
Picocli is a powerful and easy to use Java command line parser framework, which can easily create command line interfaces and tools.It provides many characteristics, including automatic completion, inner provinces, nested and sub -commands, parameter verification, etc.This article will introduce the technical principles of the Picocli framework and the Java code example using the framework.
1. Definition of command line parameters of the annotation drive:
The Picocli framework uses annotations to define command line parameters.By adding annotations on the fields or methods of the Java class, the definition of command line options, parameters and commands can be achieved.The following is a simple example:
import picocli.CommandLine;
import picocli.CommandLine.Command;
import picocli.CommandLine.Option;
import picocli.CommandLine.Parameters;
@Command(name = "myapp", description = "This is my app")
public class MyApp implements Runnable {
@Option(names = {"-v", "--verbose"}, description = "Enable verbose mode")
private boolean verbose;
@Parameters(description = "This is a parameter")
private String parameter;
public void run() {
if (verbose) {
System.out.println("Running in verbose mode");
}
System.out.println("Parameter: " + parameter);
}
public static void main(String[] args) {
CommandLine.run(new MyApp(), args);
}
}
In the above example, a command line application called "MyApp" is defined by adding annotations to the class and fields."-v" and "--Verbose" are the command line options for enabled detailed mode."Parameter" is a command line parameter that is used to pass the parameter value.By calling the method of `Commandline.run (), the command line parameters can be parsed and the corresponding operation can be performed.
2. Automatic completion:
The Picocli framework uses Java Service Provider Interface (SPI) to achieve automatic completion function.It will be allocated to the logic of the logic of automatic completion by the classification of `Picoclii.AutocompleteteCommandCompletion` interface to` Meta-Inf/Services/Picocli.AutocompletecommandCompleTion '.
The following is an example of automatic completing the MySQL command:
import picocli.AutoComplete.GenerateCommandCompletion;
public class MySQLAutoComplete implements GenerateCommandCompletion {
public Iterable<String> generateCompletionScript(String commandName) {
// Return the script for automatic completion of the MySQL command
List<String> completions = new ArrayList<String>();
completions.add("mysql");
completions.add("mysqldump");
completions.add("mysqladmin");
// ...
return completions;
}
}
In the above example, a class that realizes a class that implements the `GenerateCommandCompleTion` interface to generate a script used to automatically fill the MySQL command.By adding the full class of this class to the `meta-inF/Services/Picocli.Autocomplete.gieneratecommandCompletion` file, the Picocli framework can be configured to use this class to achieve automatic complement function.
3. Jested and sub -commands:
The Picocli framework supports nested and sub -commands, which can create complex command line tools.By adding the `@Command` annotation to the Java class, and nested it in the definition of the parent command, the nested and sub -command function can be implemented.
The following is an example of nested and sub -commands:
import picocli.CommandLine;
import picocli.CommandLine.Command;
@Command(name = "parent", subcommands = {ChildCommand.class})
public class ParentCommand implements Runnable {
public void run() {
System.out.println("Parent command executed");
}
public static void main(String[] args) {
CommandLine.run(new ParentCommand(), args);
}
}
@Command(name = "child")
public class ChildCommand implements Runnable {
public void run() {
System.out.println("Child command executed");
}
}
In the above example, a parent command named "Parent" and a sub -command called "Child" are defined.By calling the method of `Commandline.run (), the command line parameters can be parsed and the corresponding commands can be executed.When executing the "Parent" command, the printed "Parent Command Execute" will be printed; when executing the "Parent Child" command, it will print "Child Command Executed".
Summarize:
Picocli is a powerful and easy -to -use Java command line analysis framework, which can help developers easily create command line interfaces and tools.Its technical principles include the definition of command line parameters, the implementation of automatic completion functions, and the characteristics of supporting nested and sub -commands.Through the above technical principles and Java code examples, developers can better understand and use the Picocli framework.
