@AuraEnabled
    public static List<Lead> findByLastName(String searchKey) {
        String lastName = '%' + searchKey + '%';
        return [SELECT Id, LastName, Company FROM Lead WHERE LastName LIKE :lastName ORDER BY LastModifiedDate DESC LIMIT 50];
    }

<!-- コンポーネントイベント -->
<aura:event type="COMPONENT">
    <aura:attribute name="searchKey" type="String"/>
</aura:event>

<aura:component controller="LeadController" implements="force:appHostable">

    <aura:attribute name="leads" type="Lead[]"/>
    <aura:handler name="init" value="{!this}" action="{!c.doInit}"/>

    <!-- コンポーネントイベント登録 -->
    <aura:registerEvent name="searchKeyChange" type="c:SearchKeyChangeEvent"/>
    <!-- コンポーネントイベント購読 -->
    <aura:handler name="searchKeyChange" action="{!c.search}"/>

    <h3>リード表示</h3>
    <ui:inputText aura:id="searchkey" label="姓" labelClass="assistiveText" placeholder="姓で検索" keyup="{!c.searchKeyChange}" updateOn="keyup"/>
    <ui:button label="更新" press="{!c.refresh}"/>
    <ul>
        <aura:iteration items="{!v.leads}" var="lead">
            <li>
                <p>
                    {!lead.Company}<br/>
                    {!lead.LastName}
                </p>
            </li>
        </aura:iteration>
    </ul>
</aura:component>

({
    // initイベント処理
    doInit: function(component, event, helper) {
        helper.getLeads(component);
    },
    // 更新ボタンクリック
    refresh: function(component, event, helper) {
        var searchKey = component.find("searchkey").get("v.value");
        if ($A.util.isEmpty(searchKey)) {
            searchKey = "";
        }
        helper.getLeadsByName(component, searchKey);
    },
    // keyup
    searchKeyChange: function(component, event, helper) {
        // コンポーネントイベント発火
        var searchKeyChangeEvent = component.getEvent("searchKeyChange");
        searchKeyChangeEvent.setParams({
            "searchKey": component.find("searchkey").get("v.value"),
        });
        searchKeyChangeEvent.fire();
    },
    // コンポーネントイベント処理
    search: function(component, event, helper) {
        // イベントの属性値を取得
        var searchKey = event.getParam("searchKey");
        if ($A.util.isEmpty(searchKey)) {
            searchKey = "";
        }
        helper.getLeadsByName(component, searchKey);
    },
})

({
    getLeads: function(component) {
        var action = component.get("c.findAll");
        action.setCallback(this, function(a){
            component.set("v.leads", a.getReturnValue());
        });
        $A.enqueueAction(action);
    },
    getLeadsByName: function(component, searchKey) {
        var action = component.get("c.findByLastName");
        action.setParams({
            "searchKey": searchKey
        });
        action.setCallback(this, function(a){
            component.set("v.leads", a.getReturnValue());
        });
        $A.enqueueAction(action);
    }
})

event.getParam("searchKey")