Document bean validation constraints in help()

Fixes #147

spring-shell-core/src/main/java/org/springframework/shell/ParameterDescription.java

@@ -23,6 +23,8 @@ import java.util.Optional;
 
 import org.springframework.core.MethodParameter;
 
+import javax.validation.metadata.ElementDescriptor;
+
 /**
  * Encapsulates information about a shell invokable method parameter, so that it can be documented.
  *
@@ -75,6 +77,14 @@ public class ParameterDescription {
 	 */
 	private String help = "";
 
+	/**
+	 * Allows discovery of bean validation constraints for the command parameter.
+	 * <p>Note that most often, constraints will directly come from parameter constraints,
+	 * but sometimes (<em>e.g.</em> in case of one method argument mapping to multiple
+	 * command options) may come from property constraints.</p>
+	 */
+	private ElementDescriptor elementDescriptor;
+
 	public ParameterDescription(MethodParameter parameter, String type) {
 		this.parameter = parameter;
 		this.type = type;
@@ -123,6 +133,17 @@ public class ParameterDescription {
 		return this;
 	}
 
+	/**
+	 * @return an ElementDescriptor used to discover constraints. May be {@literal null}.
+	 */
+	public ElementDescriptor elementDescriptor() {
+		return this.elementDescriptor;
+	}
+
+	public ParameterDescription elementDescriptor(ElementDescriptor descriptor) {
+		this.elementDescriptor = descriptor;
+		return this;
+	}
 
 	public String type() {
 		return type;

spring-shell-core/src/main/java/org/springframework/shell/Shell.java

@@ -29,6 +29,7 @@ import java.util.stream.Collectors;
 import javax.annotation.PostConstruct;
 import javax.validation.ConstraintViolation;
 import javax.validation.Validation;
+import javax.validation.Validator;
 import javax.validation.executable.ExecutableValidator;
 
 import org.springframework.beans.factory.annotation.Autowired;
@@ -54,6 +55,9 @@ public class Shell implements CommandRegistry {
 	@Autowired
 	protected ApplicationContext applicationContext;
 
+	@Autowired(required = false)
+	private Validator validator = Validation.buildDefaultValidatorFactory().getValidator();
+
 	protected Map<String, MethodTarget> methodTargets = new HashMap<>();
 
 	protected List<ParameterResolver> parameterResolvers;
@@ -63,9 +67,6 @@ public class Shell implements CommandRegistry {
 	 */
 	protected static final Object UNRESOLVED = new Object();
 
-	private final ExecutableValidator executableValidator = Validation
-		.buildDefaultValidatorFactory().getValidator().forExecutables();
-
 	public Shell(ResultHandler resultHandler) {
 		this.resultHandler = resultHandler;
 	}
@@ -232,7 +233,7 @@ public class Shell implements CommandRegistry {
 				throw new IllegalStateException("Could not resolve " + methodParameter);
 			}
 		}
-		Set<ConstraintViolation<Object>> constraintViolations = executableValidator.validateParameters(
+		Set<ConstraintViolation<Object>> constraintViolations = validator.forExecutables().validateParameters(
 			methodTarget.getBean(),
 			methodTarget.getMethod(),
 			args

spring-shell-core/src/main/java/org/springframework/shell/SpringShellAutoConfiguration.java

@@ -27,6 +27,9 @@ import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.support.DefaultConversionService;
 import org.springframework.shell.result.ResultHandlerConfig;
 
+import javax.validation.Validation;
+import javax.validation.Validator;
+
 /**
  * Creates supporting beans for running the Shell
  */
@@ -40,10 +43,15 @@ public class SpringShellAutoConfiguration {
 		return new DefaultConversionService();
 	}
 
+	@Bean
+	@ConditionalOnMissingBean(Validator.class)
+	public Validator validator() {
+		return Validation.buildDefaultValidatorFactory().getValidator();
+	}
+
 	@Bean
 	public Shell shell(@Qualifier("main") ResultHandler resultHandler) {
 		return new Shell(resultHandler);
 	}
 
-
 }