Rails flash messages in Java

Question

What's the best way to achieve Rails-like flash messages such as "Update successful" http://api.rubyonrails.org/classes/ActionController/Flash.html) in the Java world? I'm using Spring MVC.

Answer 1

I have done just that in Spring MVC with a session scoped bean.

public class FlashImpl implements Flash, Serializable{

private static final long serialVersionUID = 1L;

private static final String ERROR = "error";
private static final String WARNING = "warning";
private static final String NOTICE = "notice";

private String message;
private String klass;

public void message(String klass, String message) {
    this.klass = klass;
    this.message = message;
}

public void notice(String message) {
    this.message(NOTICE, message);
}

public void warning(String message) {
    this.message(WARNING, message);
}

public void error(String message) {
    this.message(ERROR, message);
}

public boolean isEmptyMessage() {
    return message == null;
}

public void clear() {
    this.message = null;
    this.klass = null;
}

public String getMessage() {
    String msg = message;
    this.clear();
    return msg;
}

public void setMessage(String message) {
    this.message = message;
}

public String getKlass() {
    return klass;
}

public void setKlass(String klass) {
    this.klass = klass;
}}

The trick is in consumming the message once it's been read for the first time. This way it can survive to a redirect after post.

I am assuming that there will be only one type of message for request!. If you don't want this you could create a hashmap as already suggested.

I inject this bean in my controllers (actually I inject it in a base controller inherited by all the others).

In your JSP you have to add some code like this:

<c:if test="${!flash.emptyMessage}" >
    <div class="${flash.klass}">${fn:escapeXml(flash.message)}</div>
</c:if>

Answer 2

I would recommend implementing this as a session-wide HashTable, with string keys mapping to custom FlashItem objects. The FlashItem will simply contain the object or string you're storing plus a boolean value, possibly called IsNew, which should be set to true when you insert a new item into the HashTable.

On each page load you then iterate the HashTable, set any IsNew = true items to false, and delete any items where IsNew is already false. That should give you a work-alike to Rails's flash feature.