springboot加载命令行参数ApplicationArguments的实现

file:
  location: /data/files

@Component
public class upload {
    @Value("${file.location}")
    private String fileLocation; // 文件路径/data/files
    
    public void upload(File file) {
        // 将文件保存到fileLocation中。
    }
}

@SpringBootApplication
public class ArgumentApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext applicationContext = SpringApplication.run(ArgumentApplication.class, args);

        // 获取应用程序参数
        ApplicationArguments applicationArguments =(ApplicationArguments)applicationContext
            																	.getBean("springApplicationArguments");
        // 获取命令行中name的配置
        List<String> name = applicationArguments.getOptionValues("name");
        System.out.println(name);
    }
}

@Component
public class ComponentA {

    @Value("${name}")
    private String name;

    public ComponentA() {
    }

    public String getName() {
        return name;
    }
}

@SpringBootApplication
public class ArgumentApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext applicationContext = SpringApplication.run(ArgumentApplication.class, args);

        // 从配置文件中获取
        ComponentA componentA = (ComponentA) applicationContext.getBean("componentA");
        System.out.println(componentA.getName());
    }
}

@SpringBootApplication
public class ArgumentApplication {

    public static void main(String[] args) {
        SpringApplication.run(ArgumentApplication.class, args);
    }
}

public ConfigurableApplicationContext run(String... args) {
    // ...
    SpringApplicationRunListeners listeners = getRunListeners(args);
	// ...
    ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
    // ...
}

public class DefaultApplicationArguments implements ApplicationArguments {

	private final Source source;
	private final String[] args;

	public DefaultApplicationArguments(String... args) {
		Assert.notNull(args, "Args must not be null");
		this.source = new Source(args);
		this.args = args;
	}
	// ...
	private static class Source extends SimpleCommandLinePropertySource {

		Source(String[] args) {
			super(args);
		}
        // ...
	}
}

public class SimpleCommandLinePropertySource extends CommandLinePropertySource<CommandLineArgs> {

	public SimpleCommandLinePropertySource(String... args) {
		super(new SimpleCommandLineArgsParser().parse(args));
	}

	public SimpleCommandLinePropertySource(String name, String[] args) {
		super(name, new SimpleCommandLineArgsParser().parse(args));
	}
}

class SimpleCommandLineArgsParser {

	public CommandLineArgs parse(String... args) {
		CommandLineArgs commandLineArgs = new CommandLineArgs();
		for (String arg : args) {
            // 以 -- 开头的应用程序参数
			if (arg.startsWith("--")) {
				String optionText = arg.substring(2);
				String optionName;
				String optionValue = null;
				int indexOfEqualsSign = optionText.indexOf('=');
				if (indexOfEqualsSign > -1) {
                    // --key=value这种形式的参数
					optionName = optionText.substring(0, indexOfEqualsSign);
					optionValue = optionText.substring(indexOfEqualsSign + 1);
				}
				else {
                    // --key这种形式的参数
					optionName = optionText;
				}
				if (optionName.isEmpty()) {
					throw new IllegalArgumentException("Invalid argument syntax: " + arg);
				}
				commandLineArgs.addOptionArg(optionName, optionValue);
			}
			else {
                // 不以 -- 开头的应用程序参数
				commandLineArgs.addNonOptionArg(arg);
			}
		}
		return commandLineArgs;
	}
}

class CommandLineArgs {
	// 保存 --key=value  和 --key这两种类型的应用程序参数
	private final Map<String, List<String>> optionArgs = new HashMap<>();
    // 保存 key 这一种类型的应用程序参数
	private final List<String> nonOptionArgs = new ArrayList<>();
}

public abstract class CommandLinePropertySource<T> extends EnumerablePropertySource<T> {

	public static final String COMMAND_LINE_PROPERTY_SOURCE_NAME = "commandLineArgs";

	public CommandLinePropertySource(T source) {
		super(COMMAND_LINE_PROPERTY_SOURCE_NAME, source);
	}
}

public abstract class EnumerablePropertySource<T> extends PropertySource<T> {
    
	public EnumerablePropertySource(String name, T source) {
		super(name, source);
	}
}

public abstract class PropertySource<T> {

	protected final String name;

	protected final T source;
    
	public PropertySource(String name, T source) {
		Assert.hasText(name, "Property source name must contain at least one character");
		Assert.notNull(source, "Property source must not be null");
		this.name = name;
		this.source = source;
	}
}

public ConfigurableApplicationContext run(String... args) {
    // ...
	ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
	ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
	// ...
}

private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,
			DefaultBootstrapContext bootstrapContext, ApplicationArguments applicationArguments) {
    // Create and configure the environment
    ConfigurableEnvironment environment = getOrCreateEnvironment();
    configureEnvironment(environment, applicationArguments.getSourceArgs());
}

protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) {
    // ...
    configurePropertySources(environment, args);
    // ...
}

// 将应用程序设置到environment对象中，与配置文件中的参数处于同一environment对象中，因此可以通过@Value注解获取参数配置
protected void configurePropertySources(ConfigurableEnvironment environment, String[] args) {
    MutablePropertySources sources = environment.getPropertySources();
    DefaultPropertiesPropertySource.ifNotEmpty(this.defaultProperties, sources::addLast);
    if (this.addCommandLineProperties && args.length > 0) {
        String name = CommandLinePropertySource.COMMAND_LINE_PROPERTY_SOURCE_NAME;
        if (sources.contains(name)) {
            // 环境中已存在相同的配置，则进行覆盖
            PropertySource<?> source = sources.get(name);
            CompositePropertySource composite = new CompositePropertySource(name);
            composite.addPropertySource(
                new SimpleCommandLinePropertySource("springApplicationCommandLineArgs", args));
            composite.addPropertySource(source);
            sources.replace(name, composite);
        }
        else {
            sources.addFirst(new SimpleCommandLinePropertySource(args));
        }
    }
}

public ConfigurableApplicationContext run(String... args) {
    ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
    ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
    // ...
    prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
	// ...
}

private void prepareContext(DefaultBootstrapContext bootstrapContext, ConfigurableApplicationContext context,
			ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
			ApplicationArguments applicationArguments, Banner printedBanner) {
    // ...
    ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
    beanFactory.reGISterSingleton("springApplicationArguments", applicationArguments);
    // ...
}