How to validate an empty field in action method?

问题

I have an input field and a button. I want to check if the textinput is valid before executing the button action. If it is valid I will render a response message. I have a code like this:

public void submitReportRequest() {
    if(nameField!=null){
        System.out.println("aaaaaaaaaaaaa");
        submitted=true;
    }
    if(nameField == null){
        System.out.println("report name is null!!!!!!");
    }
}

but from the console I just get:

[#|2011-11-18T15:22:49.931+0200|INFO|glassfishv3.0|null|_ThreadID=21;_ThreadName=Thread-1;|aaaaaaaaaaaaa|#]

when the nameField is empty, I receive nothing in the console just page is re-rendered with the validation message of nameField. I know from the JSF life cycle if the validation phase fails then it jumps directly to the render response phase and button action is never reached. But how can I achieve my objective in this case?

回答1:

Empty submitted values default to empty strings, not null. Instead, you need to check if the string is empty by String#isEmpty():

if (nameField.isEmpty()) {
    // Name field is empty.
} else {
    // Name field is not empty.
}

You perhaps want to cover blank spaces as well. In that case, add trim():

if (nameField.trim().isEmpty()) {
    // Name field is empty or contained spaces only.
} else {
    // Name field is not empty and did not contain spaces only.
}

Note that the String#isEmpty() is introduced in Java 1.6. If you're still on Java 1.5 or older for some reason, then you need to check String#length() instead.

if (nameField.length() == 0) {
    // Name field is empty.
} else {
    // Name field is not empty.
}

However, that's not the normal way of required field validation. You should put the required="true" attribute on the input field instead.

<h:inputText id="name" value="#{bean.name}" required="true" />
<h:message for="name" />

This way JSF will validate it by itself and display the appropriate message and will skip the action method invocation.

How to validate an empty field in action method?

问题

回答1:

See also: