如何自动打印子命令结果？

Question

我有 Java 基于 cliche 库的 CLI 应用程序，我想将它迁移到 picocli。

我的应用程序基于陈词滥调，所以我有很多带有 asg.cliche.Command 注释的方法，其中 return 一些结果。陈词滥调自动打印命令方法的结果，因此结果在命令行中打印。我用 picocli.CommandLine.Command 替换了 asg.cliche.Command 注释，我看到 picocli 不打印命令方法的结果。我有以下 class:

import picocli.CommandLine;

@CommandLine.Command(subcommandsRepeatable = true)
public class Foo
{

    public static void main( String[] args )
    {
        new CommandLine( new Foo() ).execute( args );
    }

    @CommandLine.Command
    public String sayHello()
    {
        return "Hello";
    }

    @CommandLine.Command
    public String sayGoodbye()
    {
        return "GoodBye";
    }
}

当我调用 java -cp myJar.jar Foo sayHello sayGoodbye 时，我没有看到任何输出。我看到三种解决方案： 1.修改每个方法打印结果而不是return它。

import picocli.CommandLine;

@CommandLine.Command( subcommandsRepeatable = true )
public class Foo2
{

    public static void main( String[] args )
    {
        new CommandLine( new Foo2() ).execute( args );
    }

    @CommandLine.Command
    public void sayHello()
    {
        System.out.println( "Hello" );
    }

    @CommandLine.Command
    public void sayGoodbye()
    {
        System.out.println( "GoodBye" );
    }
}

我对这个解决方案不满意。我不想修改我的方法。

执行后检索结果。

public static void main( String[] args )
    {
        final CommandLine commandLine = new CommandLine( new Foo() );
        commandLine.execute( args );
        CommandLine.ParseResult parseResult = commandLine.getParseResult();
        for( CommandLine.ParseResult pr : parseResult.subcommands() )
        {
            System.out.println( pr.commandSpec().commandLine()
                .getExecutionResult()
                .toString() );
        }
    }

我发现此解决方案存在一些问题。主要问题是格式化。执行结果可以是null、数组、集合。第二个问题是在执行所有子命令后打印结果。如果第二个子命令抛出异常，那么我首先看到异常堆栈跟踪，然后我看到第一个子命令的结果。

如果有更好的解决方案，请在 Whosebug 上询问。我不相信 picocli 中没有任何启用结果打印的配置选项。

Answer 1

就个人而言，我最喜欢您的第一个解决方案，它简单易维护。也许引入一个用于打印和格式化的辅助方法，这样命令方法就可以如下所示：

    @CommandLine.Command
    public String sayGoodbye()
    {
        return printValue("GoodBye");
    }

您已经找到了CommandLine.getParseResult方法；也许辅助方法也可以帮助格式化那里。

还有第三种选择，但不幸的是，它要复杂得多：您可以创建一个自定义 IExecutionStrategy，在执行每条命令后打印其结果。它涉及从 picocli 内部复制大量代码，这不是一个真正现实的解决方案；我只是为了完整性而提到它。

// extend RunLast to handle requests for help/version and exit code stuff
class PrintingExecutionStrategy extends CommandLine.RunLast {
    @Override
    protected List<Object> handle(ParseResult parseResult) throws ExecutionException {
        // Simplified: executes only the last subcommand (so no repeating subcommands).
        // Look at RunLast.executeUserObjectOfLastSubcommandWithSameParent if you need repeating subcommands.
        List<CommandLine> parsedCommands = parseResult.asCommandLineList();
        CommandLine last = parsedCommands.get(parsedCommands.size() - 1);
        return execute(last, new ArrayList<Object>());
    }

    // copied from CommandLine.executeUserObject,
    // modified to print the execution result
    private List<Object> execute(CommandLine cmd, List<Object> executionResultList) throws Exception {
        Object command = parsed.getCommand();
        if (command instanceof Runnable) {
            try {
                ((Runnable) command).run();
                parsed.setExecutionResult(null); // 4.0
                executionResultList.add(null); // for compatibility with picocli 2.x
                return executionResultList;
            } catch (ParameterException ex) {
                throw ex;
            } catch (ExecutionException ex) {
                throw ex;
            } catch (Exception ex) {
                throw new ExecutionException(parsed, "Error while running command (" + command + "): " + ex, ex);
            }
        } else if (command instanceof Callable) {
            try {
                @SuppressWarnings("unchecked") Callable<Object> callable = (Callable<Object>) command;
                Object executionResult = callable.call();

                System.out.println(executionResult); <-------- print result

                parsed.setExecutionResult(executionResult);
                executionResultList.add(executionResult);
                return executionResultList;
            } catch (ParameterException ex) {
                throw ex;
            } catch (ExecutionException ex) {
                throw ex;
            } catch (Exception ex) {
                throw new ExecutionException(parsed, "Error while calling command (" + command + "): " + ex, ex);
            }
        } else if (command instanceof Method) {
            try {
                Method method = (Method) command;
                Object[] parsedArgs = parsed.getCommandSpec().argValues();
                Object executionResult;
                if (Modifier.isStatic(method.getModifiers())) {
                    executionResult = method.invoke(null, parsedArgs); // invoke static method
                } else if (parsed.getCommandSpec().parent() != null) {
                    executionResult = method.invoke(parsed.getCommandSpec().parent().userObject(), parsedArgs);
                } else {
                    executionResult = method.invoke(parsed.factory.create(method.getDeclaringClass()), parsedArgs);
                }

                System.out.println(executionResult); <-------- print result

                parsed.setExecutionResult(executionResult);
                executionResultList.add(executionResult);
                return executionResultList;
            } catch (InvocationTargetException ex) {
                Throwable t = ex.getTargetException();
                if (t instanceof ParameterException) {
                    throw (ParameterException) t;
                } else if (t instanceof ExecutionException) {
                    throw (ExecutionException) t;
                } else {
                    throw new ExecutionException(parsed, "Error while calling command (" + command + "): " + t, t);
                }
            } catch (Exception ex) {
                throw new ExecutionException(parsed, "Unhandled error while calling command (" + command + "): " + ex, ex);
            }
        }
        throw new ExecutionException(parsed, "Parsed command (" + command + ") is not a Method, Runnable or Callable");
    }
}

这样使用：

public static void main(String... args) {
    new CommandLine(new Foo())
        .setExecutionStrategy(new PrintingExecutionStrategy())
        .execute(args);
}

以上我不推荐。

更新：我想到了另一个，第四个选项（实际上是你的第二个解决方案的变体）。您可以指定一个不打印堆栈跟踪的自定义 IExecutionExceptionHandler，而是存储异常，以便您可以在打印命令结果后打印堆栈跟踪。像这样：

class MyHandler extends IExecutionExceptionHandler() {
    Exception exception;
    public int handleExecutionException(Exception ex,
                                         CommandLine commandLine,
                                         ParseResult parseResult) {
         //ex.printStackTrace(); // no stack trace
         exception = ex;
    }
}

这样使用：

public static void main(String... args) {
    MyHandler handler = new MyHandler();
    CommandLine cmd = new CommandLine(new Foo())
        .setExecutionExceptionHandler(handler);
    cmd.execute(args);

    ParseResult parseResult = cmd.getParseResult();
    for( ParseResult pr : parseResult.subcommands() )
    {
        System.out.println( pr.commandSpec().commandLine()
                .getExecutionResult()
                .toString() );
    }

    if (handler.exception != null) {
        handler.exception.printStackTrace();
    }
}

如何自动打印子命令结果？

How to print subcommand result automatically?

picocli