从Vaadin 8应用程序生成HTML页面，并在新窗口中打开

Question

从我的Vaadin 8网络应用程序，我希望用户能够通过单击按钮在另一个窗口中打开报告。内容将由Vaadin应用程序使用纯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对象打开一个新窗口。但是那个窗口包含一个Vaadin UI子类，而我想生成自己的HTML内容。

传递信息（例如数据库标识符值）的加值点。

Answer 1

这是一个完整的示例应用程序，内置在Vaadin 8.5.1中。我们在TextField中将UUID作为文本呈现，其中一个按钮打开第二个窗口，显示由我们的Vaadin应用程序生成的HTML网页，而不使用Vaadin小部件或布局。来自该字段的id将传递到新窗口，该窗口在真实应用程序中可用于数据库查找。

如手册中的该页面所示，您需要使用BrowserWindowOpener（或Link）。由于浏览器常见的安全限制，必须在用户单击按钮之前提前配置。因此，我们必须提前配置BrowserWindowOpener对象，并与按钮关联，而不是在按钮的单击侦听器中编写代码。

定义用户单击的按钮以生成报告。

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

定义要打开的新窗口的目标，它应该用作其Web地址的URL。我们想回调我们的Vaadin应用程序。因此，请在运行时获取此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”。所以我们询问当前上下文的URL（路径）。

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

我们需要将该URL缩小到我们的报告，详细说明要从数据库加载的单个Person对象。因此，我们发明person.html作为我们的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类。

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对象，我们准备定义BrowserWindowOpener。

BrowserWindowOpener webPageOpener = new BrowserWindowOpener( resource );

让我们配置一些属性，例如要打开的窗口的标题。

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

我们希望传递要从数据库中检索的“人”行的ID，然后显示在我们生成的网页中。

将此类信息作为URL中的query string中的参数传递的一种方法。所以我们URL的最后一部分看起来像person.html?person_id= f0e32ddc-18ed-432c-950b-eda3f3e4a80d。该值必须是文本的，因此我们使用表示UUID的128位的规范36字符十六进制字符串作为我们的数据库标识符。我们给这个值一个任意的键名，比如person_id。

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

我们可以设置要打开的新窗口的大小。我们将在运行时使其与用户当前窗口的大小相同。并且我们将使窗口可调整大小，因此用户可以将其拉伸更大或更小。我们希望最终得到width=800,height=600,resizable等字符串中描述的窗口特征。我们将在运行时插入宽度和高度。

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".

我们完成了配置要打开的新窗口。由于用户在事件监听器中按下按钮而不能像通常对其他行为那样调用窗口打开，因此我们必须提前将开启者与按钮相关联。

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

为了好玩，我们可以预览新窗口要调用的URL。在实际工作中，使用SLF4J和LogBack等日志框架。对于此演示，我们转储到控制台。

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

好的，我们现在有一个开启器设置的按钮，要求生成基于HTML的报告。接下来我们必须生成该报告。要做到这一点，请告诉我们的Vaadin应用程序预期使用我们在上面指定的person.html URL的传入URL。我们通过实现RequestHandler接口来实现这一点。见the manual。

在我们的RequestHandler中，我们做了四件事：

检索作为新窗口中打开的URL的查询字符串中的参数传递的UUID的十六进制字符串。
从该十六进制字符串重构UUID对象。
将UUID对象传递给生成要在此新窗口中显示的HTML的例程。
通过将HTML传递给VaadinResponse对象在新窗口中显示该HTML，该对象通过Java Servlet技术传递回用户的Web浏览器。

我们必须实例化我们的RequestHandler实现，并使用用户的会话注册实例，这是一个VaadinSession对象。

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
            }
        } );

填写该方法以生成HTML。

// 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>

为了您的方便，这里是整个Vaadin 8应用程序，MyUI.java文件的内容首先由Vaadin有限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类来完成此操作：

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：使用我以前的方法我遇到一个问题，由于HTTP 400错误没有显示弹出页面。这是由于http标头大小太大（是的，我生成了一个大的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);

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