<h:form id="myForm" prependId="false">
     <div class="input-field col s12 m7 l8">
        <p:inputTextarea styleClass="materialize-textarea" id="q" value="#{documentController.motSearch}"/>
        <label for="q">Mot/phrase à chercher</label>
     </div>

  <p:commandButton id="bb" type="submit" value="Chercher"
                     action="ListeDocuments?faces-redirect=true&includeViewParams=true"/>

 </h:form>

<f:metadata>
    <f:viewParam name="searching" value="#{documentController.searching}" />
    <f:viewParam name="q" value="#{documentController.motSearch}"/>
    <f:viewAction action="#{documentController.onload}"/>
</f:metadata>

<p:dataTable id="table" tableStyleClass="hoverable striped" rows="10" paginator="true"
                             value="#{documentController.documents}" var="doc"
                             paginatorPosition="bottom" paginatorAlwaysVisible="false" styleClass="borderless">
....
</p:dataTable>

import javax.faces.bean.ManagedBean;
import javax.faces.bean.SessionScoped;

@ManagedBean
@SessionScoped
public class DocumentController implements Serializable{

private String motSearch;
private boolean searching = false;
private List<Document> documents;

public void onload()
{
    if(!searching)
    {
        motSearch = null;
        documentsListForConnectedUser();
    }
    else{
        search();
    }
}

 public void search()
 {
   // querying the database to get all the documents
   // filtering the documents list

 }

 //other methods
 //getters and setters

}