ファイルのプレビュー一覧表示

<apex:page showheader="true" sidebar="true" standardstylesheets="true" extensions="FilePreviewController" standardController="User" readOnly="false">
    <apex:pageBlock title="ファイルプレビュー" id="block">
    <apex:pageBlockSection title="パンフレット" id="blocksection" collapsible="false" >
    <apex:datatable value="{! documentWrapperList}" var="document" styleClass="table table-bordered table-condensed table-hover table-dashboard">
        <apex:column >
            <apex:outputText value="{! document.docNameForDisplay}" />
            <apex:image url="{!document.thumbnailURL}" onclick="window.open('{!document.previewURL}', '{!document.docName}', 'width=1024, height=800, menubar=no, toolbar=no, scrollbars=yes, resizable=yes');" style="width:361px;height:480px;"></apex:image>
        </apex:column>
    </apex:datatable>
    </apex:pageBlockSection>
    </apex:pageBlock>
</apex:page>

public with sharing class FilePreviewController{
    public List<DocumentWrapper> documentWrapperList {get; set;}
    private String instanceUrl = 'https://ynaganotesttest-dev-ed.my.salesforce.com';

    /*
     * コンストラクタ
     */
    public FilePreviewController(ApexPages.StandardController controller) {
        documentWrapperList = new List<DocumentWrapper>();
        excuteSearch();
    }

    /**
     * 検索実行
     */
    private void excuteSearch() {
        // ファイルのID取得
        List<ContentDocument> documentList =
            [ SELECT  Id, Title, FileExtension
              FROM ContentDocument
              WHERE parentId IN (SELECT Id FROM ContentWorkspace WHERE Name IN ('パンフレット'))
              ORDER BY LastModifiedDate DESC];

        documentWrapperList.clear();
        for(Integer i = 0; i<documentList.size(); i++){
            documentWrapperList.add(new DocumentWrapper(documentList[i],instanceUrl,i + 1));
        }
    }

    /**
     * 画面表示クラス
     */
    public class DocumentWrapper {
        public String docName { get; set; }
        public String docNameForDisplay { get; set; }
        public String thumbnailURL { get; set; }
        public String previewURL { get; set; }
        public ContentDocument doc { get; set; }
        public Integer index { get; set; }

        /**
         * コンストラクタ
         */
        public DocumentWrapper(ContentDocument contentDocument, String instanceUrl, Integer index) {
            doc = contentDocument;
            docName = contentDocument.Title + '.' + contentDocument.FileExtension;
            docNameForDisplay = contentDocument.Title + '.' + contentDocument.FileExtension;
            previewURL = instanceUrl + '/' + contentDocument.Id;
            this.index = index;

            setThumbnailURL(contentDocument,instanceUrl);
        }

        /**
         * ThumbnailURLをCallOutで取得
         */        
        private void setThumbnailURL(ContentDocument contentDocument,String instanceUrl) {
            thumbnailURL = '';
            //HTTPリクエストの作成
            HttpRequest req = new HttpRequest();
            String endPoint = instanceUrl + '/services/data/v40.0/connect/files/'+ contentDocument.Id + '/previews/big-thumbnail?startPageNumber=0&endPageNumber=0';
            req.setEndpoint ( endPoint ) ;
            req.setHeader('Authorization', 'Bearer ' + UserInfo.getSessionId());
            req.setMethod ( 'GET' ) ;

            //HTTPリクエストの送信
            HttpResponse res = new Http().send(req) ;

            JSONparser parser = JSON.createparser(res.getBody());
            while (parser.nextToken() != null) {
                if (parser.getCurrentToken() == JSONToken.START_ARRAY){
                    while(parser.nextToken() != null){
                        if(parser.getCurrentToken() == JSONToken.START_OBJECT){
                            InnnerPreview ip = (InnnerPreview)parser.readvalueas(InnnerPreview.class);
                            thumbnailURL = ip.previewUrl;
                        }
                    }
                }
            }
        }
    }

   /**
    * レスポンスを加工する為のインナークラス
    */   
    private class InnnerPreview {
        Integer pageNumber;
        String previewUrl;
    }
}