Pretty print bean validation errors

Fixes #137

spring-shell-samples/src/main/java/org/springframework/shell/samples/jcommander/Args.java

@@ -21,6 +21,8 @@ import java.util.List;
 
 import com.beust.jcommander.Parameter;
 
+import javax.validation.constraints.Min;
+
 /**
  * An example straight from the JCommander documentation.
  *
@@ -31,6 +33,7 @@ public class Args {
 	@Parameter
 	private List<String> parameters = new ArrayList<>();
 
+	@Min(3)
 	@Parameter(names = { "-log", "-verbose" }, description = "Level of verbosity")
 	private Integer verbose = 1;
 

spring-shell-samples/src/main/java/org/springframework/shell/samples/jcommander/JCommanderCommands.java

@@ -20,6 +20,8 @@ import org.springframework.shell.standard.ShellComponent;
 import org.springframework.shell.standard.ShellMethod;
 import org.springframework.shell.standard.ShellOption;
 
+import javax.validation.Valid;
+
 /**
  * A class with JCommander commands.
  *
@@ -29,7 +31,7 @@ import org.springframework.shell.standard.ShellOption;
 public class JCommanderCommands {
 
 	@ShellMethod("Bind parameters to JCommander POJO.")
-	public String jcommander(@ShellOption(optOut = true) Args args) {
+	public String jcommander(@ShellOption(optOut = true) @Valid Args args) {
 		return "You said " + args;
 	}
 }

spring-shell-samples/src/main/java/org/springframework/shell/samples/standard/Commands.java

@@ -30,6 +30,8 @@ import org.springframework.shell.standard.ShellOption;
 import org.springframework.shell.standard.ValueProviderSupport;
 import org.springframework.stereotype.Component;
 
+import javax.validation.constraints.Size;
+
 /**
  * Example commands for the Shell 2 Standard resolver.
  *
@@ -44,7 +46,7 @@ public class Commands {
 	}
 
 	@ShellMethod("It's cool.")
-	public String foo(String bar) {
+	public String foo(@Size(min = 2) String bar) {
 		return bar;
 	}