<apex: messages> Component in Visualforce Page

The <apex: messages> is another important component for displaying all the messages(error or warning) generated for all the components on the VF page. If we do not specify the <apex: messages> component on the VF page, all the error and warning messages will be visible only in debug logs, not in UI(VF Page).

The <apex: messages> component has the following attributes on VF Page:

1. dir

The dir is a string-type attribute used to specify the direction in which the generated HTML component should be read. RTL and LTR are the two possible values for this attribute.

Syntax:

2. globalOnly

The globalObly is a Boolean-type attribute that specifies whether only messages that are not associated with any client ID are displayed. The boolean value false is set as a default value for this attribute.

Syntax:

3. id

The id is a string-type attribute, i.e., a unique identifier that allows this component to be referenced by other components on the page.

Syntax:

4. lang

The lang is a string-type attribute used to specify the base language for the generated HTML output. The "en" and "en-US" are the two possible values for this attribute.

Syntax:

5. rendered

The rendered is a Boolean-type attribute that specifies whether this component should be rendered on the page. The boolean value true is set as a default value for this attribute.

Syntax:

6. style

The style is a string-type attribute used to specify the inline CSS applied to this component to display the message.

Syntax:

7. styleClass

The styleClass is a string-type attribute used to specify the CSS stylesheet applied to this component to display the message.

Syntax:

8. title

The title is a string-type attribute used to specify the text displayed when the mouse pointer hovers over this component.

Syntax:

9. layout

The layout is a string-type attribute used to specify the layout type used to display the error messages. The "list" or "table" are the two possible values for this attribute. The "list" is set as a default value for this attribute.

Syntax:

Let's take an example to understand how we can use this component on the VF page:

ApexMessagesExample.vfp

<!-- apex page to elaborate the use of apex messages component-->
<apex:page controller="ApexMessagesExampleController" tabStyle="Account">
    <!-- user style tag to override the standard style-->
    <style>
        .errorMessages { 
        	color: blue; 
        	font-weight: strong;
        }
    </style>
    <!-- use apex form to display account information-->
    <apex: form >
        <apex:pageBlock title="Hello {!$User.FirstName+' '+$User.LastName}!">
            New page for the {!name}. <br/>
            Showing information of {!acc.name} Account.
            <br/>
            <b>Note: </b>Enter an alphabetic character, then click Save to see what happens.
            <p>
                Number of Locations: 
                <apex:inputField value="{!acc.NumberofLocations__c}" id="Location_validation"/> 
            </p>
            <p>Number of Employees: <apex:inputField value="{!acc.NumberOfEmployees}" id="Employee_validation"/></p>
            <p/> 
            <apex:commandButton action="{!save}" value="Save"/>    
            <p/>
            <apex:messages styleClass="errorMessages"/> <p/>  
        </apex:pageBlock>  
    </apex: form>  
</apex: page> 

ApexMessagesExampleController.apxc

public class ApexMessagesExampleController {
    // create an instance of Account
    public Account acc{get;set;}
    public string recId;
    
    //default constructor
    public ApexMessagesExampleController(){
        recId = ApexPages.currentPage().getParameters().get('id');
        acc = [select id, name, numberofemployees, numberoflocations__c from Account where id = :recId];
    }
    
    // create save() method
    public PageReference save() {
        try{
            update acc;
        }
        catch(DmlException ex){
            ApexPages.addMessages(ex);
        }
        return null;
    }
    
    // getter to get the name of the controller
    public String getName() { 
        return 'ApexMessagesExampleController';
    }
}

Output