Save an attachment in APEX

Attachment field allows users to be able to attach notes and attachments to custom object records. This allows you to attach external documents to any object record, in much the same way that you can add a PDF or photo as an attachment to an email. This option is only available when you are creating a new object. Here I have an example for save an attachment in APEX.

/*****Controler*****/

public class status{
private final Applicant__c applicant;
public Blob resume {get; set;}
public String contentType {get; set;}
public String fileName {get; set;}

public status(ApexPages.StandardController stdController) {
this.applicant=(Applicant__c)stdController.getRecord();
}
public PageReference saveApplication() {

  try{
        insert(applicant);                                       
   }catch(System.DMLException e){
      ApexPages.addMessages(e);
       return null;
}

if(resume!=null){
      Attachment attach=new Attachment();
      attach.Body=resume;
      attach.Name=filename;
      attach.ContentType=contentType;
      attach.ParentID=applicant.id;
    try {
          insert(attach);
      } catch(System.DMLException e) {
          ApexPages.addMessages(e);
          return null;
      }
  }
  PageReference p = Page.Confirmpage;
        p.setRedirect(true);
        return p;                    
}
} 

/**Controller**/

<apex:page standardController="Applicant__c" extensions="status">
<apex:form >
<table>
<tr>
<td>Applicant Name </td>
<td><apex:inputField value="{!Applicant__c.Name__c}"/></td>
</tr>
<tr>
<td>CV </td>
<td> <apex:inputFile accept="doc, txt, pdf" filename="{!fileName}" contentType="{!contentType}" filesize="1000" size="50" value="{!resume}"/> </td>
</tr> 
<tr>
<td></td>
<td><apex:commandButton id="submitApplicant" value="Submit" action="{!saveApplication}"/></td>
</tr>
</table>
</apex:form>
</apex:page>

You can try it with your own object and particular fields.