Java命令行解析库 Argparse4j详解编程语言

argparse4j 是 Python argparse 命令行解析器的 Java 语言移植版。

它的主要特性：


1.支持位置参数和可选参数.
2.变量数量的参数.
3.生成格式化行换行帮助消息.
4.考虑到东亚宽度自动换行时模棱两可的字符.
5.Sub-commands,git添加.
6.可定制的选项前缀字符,例如.“+ f”和“/ h”.
7.打印帮助信息的默认值.
8.选择从给定的值的集合.
9.从选项字符串类型转换.
10.可以直接赋值到用户定义的类中使用注释.
11.组参数,这样它将打印在更可读的方式帮助信息.

示例代码：

import java.io.IOException;

import java.nio.ByteBuffer;

import java.nio.channels.ByteChannel;

import java.nio.file.Files;

import java.nio.file.Path;

import java.nio.file.Paths;

import java.nio.file.StandardOpenOption;

import java.security.MessageDigest;

import java.security.NoSuchAlgorithmException;

import net.sourceforge.argparse4j.ArgumentParsers;

import net.sourceforge.argparse4j.inf.ArgumentParser;

import net.sourceforge.argparse4j.inf.ArgumentParserException;

import net.sourceforge.argparse4j.inf.Namespace;

public class Checksum {

    public static void main(String[] args) {

        ArgumentParser parser = ArgumentParsers.newArgumentParser(“Checksum”)

                .defaultHelp(true)

                .description(“Calculate checksum of given files.”);

        parser.addArgument(“-t”, “–type”)

                .choices(“SHA-256”, “SHA-512”, “SHA1”).setDefault(“SHA-256”)

                .help(“Specify hash function to use”);

        parser.addArgument(“file”).nargs(“*”)

                .help(“File to calculate checksum”);

        Namespace ns = null;

        try {

            ns = parser.parseArgs(args);

        } catch (ArgumentParserException e) {

            parser.handleError(e);

            System.exit(1);

        }

        MessageDigest digest = null;

        try {

            digest = MessageDigest.getInstance(ns.getString(“type”));

        } catch (NoSuchAlgorithmException e) {

            System.err.printf(“Could not get instance of algorithm %s: %s”,

                    ns.getString(“type”), e.getMessage());

            System.exit(1);

        }

        for (String name : ns.

     getList(“file”)) {

            Path path = Paths.get(name);

            try (ByteChannel channel = Files.newByteChannel(path,

                    StandardOpenOption.READ);) {

                ByteBuffer buffer = ByteBuffer.allocate(4096);

                while (channel.read(buffer) > 0) {

                    buffer.flip();

                    digest.update(buffer);

                    buffer.clear();

                }

            } catch (IOException e) {

                System.err

                        .printf(“%s: failed to read data: %s”, e.getMessage());

                continue;

            }

            byte md[] = digest.digest();

            StringBuffer sb = new StringBuffer();

            for (int i = 0, len = md.length; i < len; ++i) {

                String x = Integer.toHexString(0xff & md[i]);

                if (x.length() == 1) {

                    sb.append(“0”);

                }

                sb.append(x);

            }

            System.out.printf(“%s  %s/n”, sb.toString(), name);

        }

    }

}

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