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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