从 Vaadin 8 应用生成 HTML 页面，并在新的 window 中打开

Question

在我的 Vaadin 8 网络应用程序中，我希望用户能够通过单击按钮在另一个 window 中打开报告。内容将由 Vaadin 应用程序使用普通 HTML5 而不是使用 Vaadin 小部件生成。

Vaadin 8 手册有一页 Handling Browser Windows。它显示了使用 BrowserWindowOpener 对象打开一个新的 window。但是 window 包含一个 Vaadin UI 子类，而我想生成我自己的 HTML 内容。

传递数据库标识符值等信息的奖励积分。

Answer 1

这是在 Vaadin 8.5.1 中构建的完整示例应用程序。我们在 TextField 中将 UUID 作为文本显示，并使用一个按钮打开第二个 window，显示由我们的 Vaadin 应用程序生成的带有 HTML 的网页，而无需使用 Vaadin 小部件或布局。来自那个字段的 id 被传递给新的 window，它在真实的应用程序中可以用于数据库查找。

如手册中该页所示，您确实需要使用 BrowserWindowOpener (or a Link)。这必须提前配置，在用户单击按钮之前，因为浏览器通用的安全限制。因此，与其在按钮的点击侦听器中编写代码，不如我们必须提前配置 BrowserWindowOpener object，并与按钮相关联。

定义用户单击以生成报告的按钮。

Button webPageButton = new Button( "Generate Person report" );

定义要打开的新 window 的目的地，URL 它应该用作其网址。我们想回调我们的 Vaadin 应用程序。因此在运行时获取此 Web 应用程序的 URL。 Java Servlet 术语中我们的 Web 应用程序的技术术语是“上下文”。所以我们向当前上下文询问其 URL （路径）。

String servletPath = VaadinServlet.getCurrent().getServletContext().getContextPath(); // URL for this web app at runtime.

我们需要将 URL 缩小到我们的报告，详细说明要从数据库加载的单个 Person object。所以我们发明 person.html 作为我们 URL 中请求的资源。

我们想要在不调用 Vaadin 小部件的情况下请求动态生成的 HTML 页面，因此我们使用 ExternalResource class.

Resource resource = new ExternalResource( servletPath + "/person.html" );  // Defining an external resource as a URL that is not really so external -- will call back into this same web app.

有了 Resource object，我们就可以定义 BrowserWindowOpener.

BrowserWindowOpener webPageOpener = new BrowserWindowOpener( resource );

我们来配置它的一些属性，比如要打开的window的标题

webPageOpener.setWindowName( "Person ID: " + personUuid.getValue() );  // Set title of the new window to be opened.

并且我们要传递要从数据库中检索的“人员”行的 ID，然后显示在我们生成的网页中。

一种将诸如此类的信息作为参数传递到 query string on the URL. So the last part of our URL will look something like person.html?person_id= f0e32ddc-18ed-432c-950b-eda3f3e4a80d. This value must be textual, so we use the canonical 36-character hex string representing the 128-bits of a UUID 作为我们的数据库标识符的方法。我们给这个值一个任意的键名，例如 person_id .

String param = "person_id";
webPageOpener.setParameter( param , personUuid.getValue() );

我们可以设置新window打开的大小。我们将在运行时使其与用户当前的 window 大小相同。我们将使 window 可调整大小，以便用户可以将其拉伸得更大或更小。我们希望以 width=800,height=600,resizable 等字符串中描述的 window 特征结束。我们将在运行时插入该宽度和高度。

String windowFeaturesString = String.format( "width=%d,height=%d,resizable" , Page.getCurrent().getBrowserWindowWidth() , Page.getCurrent().getBrowserWindowHeight() ) ; // Same size as original window.
webPageOpener.setFeatures( windowFeaturesString );  // Example: "width=800,height=600,resizable".

我们已完成配置要打开的新 window。由于 window-opening 不能像通常对其他行为那样由用户在事件侦听器中作为 button-click 的结果调用，因此我们必须提前将开启器与按钮相关联。

webPageOpener.extend( webPageButton ); // Associate opener with button.

为了好玩，我们可以预览 URL 将被新的 window 调用。在实际工作中，这里使用日志框架，例如SLF4J and LogBack。对于这个演示，我们转储到控制台。

System.out.println( "TRACE BrowserWindowOpener URL: " + webPageOpener.getUrl() );

很好，我们现在有一个带有开场白的按钮，要求生成 HTML-based 报告。接下来我们必须生成该报告。为此，请告诉我们的 Vaadin 应用程序期望传入的 URL 带有我们在上面指定的 person.html URL。我们通过实施 RequestHandler interface. See the manual.

来做到这一点

在我们的 RequestHandler 中，我们做了四件事：

检索在新 window 打开的 URL 的查询字符串中作为参数传递的 UUID 的 hex-string。
从 hex-string.

UUID

将 UUID object 传递给生成要在此新 window 中显示的 HTML 的例程。
通过将 HTML 传递给 VaadinResponse object 在新 window 中显示 HTML，后者通过 [=117= 传递回用户的 Web 浏览器] Servlet技术。

而且我们必须实例化我们的RequestHandler实现，并用用户的session注册实例，一个VaadinSessionobject.

VaadinSession.getCurrent().addRequestHandler(
        new RequestHandler() {
            @Override
            public boolean handleRequest ( VaadinSession session ,
                                           VaadinRequest request ,
                                           VaadinResponse response )
                    throws IOException {
                if ( "/panel.html".equals( request.getPathInfo() ) ) {
                    // Retrieve the hex-string of the UUID from the URL’s query string parameter.
                    String uuidString = request.getParameter( "person_id" );  // In real-work, validate the results here.
                    UUID uuid = UUID.fromString( uuidString ); // Reconstitute a `UUID` object from that hex-string. In real-work, validate the results here.
                    System.out.println( "UUID object reconstituted from string passed as parameter in query string of URL opened in new window: " + uuid );
                    // Build HTML.
                    String html = renderHtml( uuid );
                    // Send out the generated text as HTML, in UTF-8 character encoding.
                    response.setContentType( "text/html; charset=utf-8" );
                    response.getWriter().append( html );
                    return true; // We wrote a response
                } else
                    return false; // No response was written
            }
        } );

填写生成HTML的方法。

// Generate the HTML to report on the details of a `person` from the database, given the UUID of that database row.
private String renderHtml ( UUID uuid ) {
    String eol = "\n"; // End-of-line character(s) to use in the HTML.
    StringBuilder html = new StringBuilder();
    html.append( "<!DOCTYPE html>" ).append( eol );
    html.append( "<html>" ).append( eol );
    html.append( "<head>" ).append( eol );
    html.append( "<title>Person</title>" ).append( eol );
    html.append( "</head>" ).append( eol );
    html.append( "<body style='color:DarkSlateGray' >" ).append( eol );
    html.append( "<h1>Demo</h1>" ).append( eol );
    html.append( "<p>This is a drill. This is only a drill.</p>" ).append( eol );
    html.append( "<p>If this had been a real application, you would have seen some data.</p>" ).append( eol );
    html.append( "<p>Person ID: " ).append( uuid.toString() ).append( ".</p>" ).append( eol );
    html.append( "<p style='color:DimGray ; font-family: Pragmata Hack Menlo monospaced' >Report generated " ).append( Instant.now() ).append( ".</p>" ).append( eol );
    html.append( "</body>" ).append( eol );
    html.append( "</html>" ).append( eol );
    String s = html.toString();
    return s;
}

生成的 HTML 源代码如下所示：

<!DOCTYPE html>
<html>
<head>
<title>Person</title>
</head>
<body style='color:DarkSlateGray' >
<h1>Demo</h1>
<p>This is a drill. This is only a drill.</p>
<p>If this had been a real application, you would have seen some data.</p>
<p>Person ID: cc5e975b-2632-4c92-a1cb-b25085c60e60.</p>
<p style='color:DimGray ; font-family: Pragmata , Hack , Menlo , monospace' >Report generated 2018-08-05T02:33:13.028594Z.</p>
</body>
</html>

为方便起见，这里是整个 Vaadin 8 应用程序，MyUI.java 文件的内容首先由 Vaadin Ltd 公司提供的最简单的 Maven 原型生成。

package com.basilbourque.example;

import javax.servlet.annotation.WebServlet;

import com.vaadin.annotations.Theme;
import com.vaadin.annotations.VaadinServletConfiguration;
import com.vaadin.server.*;
import com.vaadin.ui.Button;
import com.vaadin.ui.Label;
import com.vaadin.ui.TextField;
import com.vaadin.ui.UI;
import com.vaadin.ui.VerticalLayout;

import java.io.IOException;
import java.time.Instant;
import java.time.ZonedDateTime;
import java.util.UUID;

/**
 * This UI is the application entry point. A UI may either represent a browser window
 * (or tab) or some part of an HTML page where a Vaadin application is embedded.
 * <p>
 * The UI is initialized using {@link #init(VaadinRequest)}. This method is intended to be
 * overridden to add component to the user interface and initialize non-component functionality.
 */
@Theme ( "mytheme" )
public class MyUI extends UI {

    @Override
    protected void init ( VaadinRequest vaadinRequest ) {
        final VerticalLayout layout = new VerticalLayout();

        TextField personUuid = new TextField( "UUID of Person:" );
        personUuid.setWidth( 22 , Unit.EM );
        personUuid.setValue( UUID.randomUUID().toString() );
        personUuid.setReadOnly( true );

        Button webPageButton = new Button( "Generate Person report" );
        webPageButton.setWidthUndefined();
        webPageButton.addClickListener( e -> {
            System.out.println( "Button clicked. " + ZonedDateTime.now() );
        } );

        // Configure web page opener object. Must be done *before* user clicks on button, not after.
        String servletPath = VaadinServlet.getCurrent().getServletContext().getContextPath(); // URL for this web app at runtime.
        Resource resource = new ExternalResource( servletPath + "/person.html" );  // Defining an external resource as a URL that is not really so external -- will call back into this same web app.
        BrowserWindowOpener webPageOpener = new BrowserWindowOpener( resource );
        webPageOpener.setWindowName( "Person ID: " + personUuid.getValue() );  // Set title of the new window to be opened.
        String param = "person_id";
        webPageOpener.setParameter( param , personUuid.getValue() );
        String windowFeaturesString = String.format( "width=%d,height=%d,resizable" , Page.getCurrent().getBrowserWindowWidth() , Page.getCurrent().getBrowserWindowHeight() ); // Same size as original window.
        webPageOpener.setFeatures( windowFeaturesString );  // Example: "width=800,height=600,resizable".
        webPageOpener.extend( webPageButton ); // Connect opener with button.
        System.out.println( "TRACE BrowserWindowOpener URL: " + webPageOpener.getUrl() );

        layout.addComponents( personUuid , webPageButton );
        setContent( layout );

        // A request handler for generating some content
        VaadinSession.getCurrent().addRequestHandler(
                new RequestHandler() {
                    @Override
                    public boolean handleRequest ( VaadinSession session ,
                                                   VaadinRequest request ,
                                                   VaadinResponse response )
                            throws IOException {
                        if ( "/person.html".equals( request.getPathInfo() ) ) {
                            // Retrieve the hex-string of the UUID from the URL’s query string parameter.
                            String uuidString = request.getParameter( "person_id" );  // In real-work, validate the results here.
                            UUID uuid = UUID.fromString( uuidString ); // Reconstitute a `UUID` object from that hex-string. In real-work, validate the results here.
                            System.out.println( "UUID object reconstituted from string passed as parameter in query string of URL opened in new window: " + uuid );
                            // Build HTML.
                            String html = renderHtml( uuid );
                            // Send out the generated text as HTML, in UTF-8 character encoding.
                            response.setContentType( "text/html; charset=utf-8" );
                            response.getWriter().append( html );
                            return true; // We wrote a response
                        } else
                            return false; // No response was written
                    }
                } );
    }

    // Generate the HTML to report on the details of a `person` from the database, given the UUID of that database row.
    private String renderHtml ( UUID uuid ) {
        String eol = "\n"; // End-of-line character(s) to use in the HTML.
        StringBuilder html = new StringBuilder();
        html.append( "<!DOCTYPE html>" ).append( eol );
        html.append( "<html>" ).append( eol );
        html.append( "<head>" ).append( eol );
        html.append( "<title>Person</title>" ).append( eol );
        html.append( "</head>" ).append( eol );
        html.append( "<body style='color:DarkSlateGray' >" ).append( eol );
        html.append( "<h1>Demo</h1>" ).append( eol );
        html.append( "<p>This is a drill. This is only a drill.</p>" ).append( eol );
        html.append( "<p>If this had been a real application, you would have seen some data.</p>" ).append( eol );
        html.append( "<p>Person ID: " ).append( uuid.toString() ).append( ".</p>" ).append( eol );
        html.append( "<p style='color:DimGray ; font-family: Pragmata , Hack , Menlo , monospace' >Report generated " ).append( Instant.now() ).append( ".</p>" ).append( eol );
        html.append( "</body>" ).append( eol );
        html.append( "</html>" ).append( eol );
        String s = html.toString();
        System.out.println( "\n\n" + s + "\n\n" );
        return s;
    }

    @WebServlet ( urlPatterns = "/*", name = "MyUIServlet", asyncSupported = true )
    @VaadinServletConfiguration ( ui = MyUI.class, productionMode = false )
    public static class MyUIServlet extends VaadinServlet {
    }
}

Answer 2

您也可以通过将 html 字符串作为参数传递给 BrowserWindowOpener 的 UI class 来执行此操作：

BrowserWindowOpener opener = new BrowserWindowOpener(MyUI.class);
opener.extend(myButtonForLaunchingNewWindow);
opener.setParameter("text",myHtmlStringWhichIJustGenerated);

public static class MyUI extends UI {
    @Override
    protected void init(VaadinRequest request) {

        String text = request.getParameter("text");
        // Have some content to print
        setContent(new Label(
                text,
                ContentMode.HTML));
    }
}

编辑：使用我以前的方法时，我遇到了一个问题，即由于 HTTP 400 错误而无法显示弹出页面。这是因为 http header 大小太大（是的，我生成了一个大 html 页面）。

我的解决方案是直接为 BrowserWindowOpener 生成 StreamResource：

StreamResource streamResource = new StreamResource((StreamResource.StreamSource) () -> 
    new ByteArrayInputStream(htmlString.getBytes()), "report.html");
BrowserWindowOpener opener = new BrowserWindowOpener(streamResource);
opener.extend(myButtonForLaunchingNewWindow);

从 Vaadin 8 应用生成 HTML 页面，并在新的 window 中打开

Generate an HTML page, and open in a new window, from a Vaadin 8 app

html

java

window

vaadin

vaadin8