Java vaadin中的缓冲图像

如何在vaadin中显示缓冲图像

我想用vaadin在图像视图中显示缓冲图像

所以，我在瓦丁的网站上看到了这个。但是，它没有完成

main.java

package com.example;


import com.vaadin.server.StreamResource;
import com.vaadin.server.StreamResource.StreamSource;
import com.vaadin.ui.Layout;





public class MainView {



public MainView()   {

// Create an instance of our stream source.
StreamSource imagesource = new MyImageSource();

// Create a resource that uses the stream source and give it
// a name. The constructor will automatically register the
// resource in the application.
StreamResource resource =
    new StreamResource(imagesource, "myimage.png");

// Create an image component that gets its contents
// from the resource.
Layout.addComponent(new Image("Image title", resource);
}
}

MyImageSource.java

package com.example;

import com.vaadin.server.StreamResource.StreamSource;
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.*;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import javax.imageio.ImageIO;

public class MyImageSource implements StreamSource {
ByteArrayOutputStream imagebuffer = null;
int reloads = 0;

// This method generates the stream contents
public InputStream getStream () {
    // Create an image
    BufferedImage image = new BufferedImage (400, 400,
                              BufferedImage.TYPE_INT_RGB);
    Graphics2D drawable = image.createGraphics();

    // Draw something static
    drawable.setStroke(new BasicStroke(5));
    drawable.setColor(Color.WHITE);
    drawable.fillRect(0, 0, 400, 400);
    drawable.setColor(Color.BLACK);
    drawable.drawOval(50, 50, 300, 300);

    // Draw something dynamic
    drawable.setFont(new Font("Montserrat",
                              Font.PLAIN, 48));
    drawable.drawString("Reloads=" + reloads, 75, 216);
    reloads++;
    drawable.setColor(new Color(0, 165, 235));
    int x= (int) (200-10 + 150*Math.sin(reloads * 0.3));
    int y= (int) (200-10 + 150*Math.cos(reloads * 0.3));
    drawable.fillOval(x, y, 20, 20);

    try {
        // Write the image to a buffer
        imagebuffer = new ByteArrayOutputStream();
        ImageIO.write(image, "png", imagebuffer);

        // Return a stream from the buffer
        return new ByteArrayInputStream(
            imagebuffer.toByteArray());
    } catch (IOException e) {
        return null;
    }
}
} 

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>

<groupId>my.vaadin.app</groupId>
<artifactId>app</artifactId>
<packaging>war</packaging>
<version>1.0-SNAPSHOT</version>
<name>app</name>

<prerequisites>
    <maven>3</maven>
</prerequisites>

<properties>
    <vaadin.version>8.0.5</vaadin.version>
    <vaadin.plugin.version>8.0.5</vaadin.plugin.version>
    <jetty.plugin.version>9.3.9.v20160517</jetty.plugin.version>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
    <!-- If there are no local customisations, this can also be "fetch" or "cdn" -->
    <vaadin.widgetset.mode>local</vaadin.widgetset.mode>
</properties>

<repositories>
    <repository>
        <id>vaadin-addons</id>
        <url>https://maven.vaadin.com/vaadin-addons</url>
    </repository>
</repositories>

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>com.vaadin</groupId>
            <artifactId>vaadin-bom</artifactId>
            <version>${vaadin.version}</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

<dependencies>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>3.0.1</version>
        <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>com.vaadin</groupId>
        <artifactId>vaadin-server</artifactId>
    </dependency>
    <dependency>
        <groupId>com.vaadin</groupId>
        <artifactId>vaadin-push</artifactId>
    </dependency>
    <dependency>
        <groupId>com.vaadin</groupId>
        <artifactId>vaadin-client-compiled</artifactId>
    </dependency>
    <dependency>
        <groupId>com.vaadin</groupId>
        <artifactId>vaadin-themes</artifactId>
    </dependency>
</dependencies>

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-war-plugin</artifactId>
            <version>3.0.0</version>
            <configuration>
                <failOnMissingWebXml>false</failOnMissingWebXml>
                <!-- Exclude an unnecessary file generated by the GWT compiler. -->
                <packagingExcludes>WEB-INF/classes/VAADIN/widgetsets/WEB-INF/**</packagingExcludes>
            </configuration>
        </plugin>
        <plugin>
            <groupId>com.vaadin</groupId>
            <artifactId>vaadin-maven-plugin</artifactId>
            <version>${vaadin.plugin.version}</version>
            <executions>
                <execution>
                    <goals>
                        <goal>update-theme</goal>
                        <goal>update-widgetset</goal>
                        <goal>compile</goal>
                        <!-- Comment out compile-theme goal to use on-the-fly theme compilation -->
                        <goal>compile-theme</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-clean-plugin</artifactId>
            <version>3.0.0</version>
            <!-- Clean up also any pre-compiled themes -->
            <configuration>
                <filesets>
                    <fileset>
                        <directory>src/main/webapp/VAADIN/themes</directory>
                        <includes>
                            <include>**/styles.css</include>
                            <include>**/styles.scss.cache</include>
                        </includes>
                    </fileset>
                </filesets>
            </configuration>
        </plugin>

        <!-- The Jetty plugin allows us to easily test the development build by
            running jetty:run on the command line. -->
        <plugin>
            <groupId>org.eclipse.jetty</groupId>
            <artifactId>jetty-maven-plugin</artifactId>
            <version>${jetty.plugin.version}</version>
            <configuration>
                <scanIntervalSeconds>2</scanIntervalSeconds>
            </configuration>
        </plugin>
    </plugins>
</build>

<profiles>
    <profile>
        <!-- Vaadin pre-release repositories -->
        <id>vaadin-prerelease</id>
        <activation>
            <activeByDefault>false</activeByDefault>
        </activation>

        <repositories>
            <repository>
                <id>vaadin-prereleases</id>
                <url>https://maven.vaadin.com/vaadin-prereleases</url>
            </repository>
            <repository>
                <id>vaadin-snapshots</id>
                <url>https://oss.sonatype.org/content/repositories/vaadin-snapshots/</url>
                <releases>
                    <enabled>false</enabled>
                </releases>
                <snapshots>
                    <enabled>true</enabled>
                </snapshots>
            </repository>
        </repositories>
        <pluginRepositories>
            <pluginRepository>
                <id>vaadin-prereleases</id>
                <url>https://maven.vaadin.com/vaadin-prereleases</url>
            </pluginRepository>
            <pluginRepository>
                <id>vaadin-snapshots</id>
                <url>https://oss.sonatype.org/content/repositories/vaadin-snapshots/</url>
                <releases>
                    <enabled>false</enabled>
                </releases>
                <snapshots>
                    <enabled>true</enabled>
                </snapshots>
            </pluginRepository>
        </pluginRepositories>
    </profile>
</profiles>

4.0.0
my.vaadin.app
应用程序
战争
1.0-快照
应用程序
3.
8.0.5
8.0.5
9.3.9.v20160517
UTF-8
1.8
1.8
地方的
瓦丁插件
https://maven.vaadin.com/vaadin-addons
com.vaadin
瓦丁波姆
${vaadin.version}
聚甲醛
进口
javax.servlet
javax.servlet-api
3.0.1
假如
com.vaadin
瓦丁服务器
com.vaadin
瓦丁推
com.vaadin
瓦丁客户机
com.vaadin
瓦丁主题
org.apache.maven.plugins
maven战争插件
3.0.0
假的
WEB-INF/classes/VAADIN/widgetsets/WEB-INF/**
com.vaadin
vaadin maven插件
${vaadin.plugin.version}
更新主题
更新WidgeSet
编译
编译主题
org.apache.maven.plugins
maven清洁插件
3.0.0
src/main/webapp/VAADIN/themes
**/styles.css
**/styles.scss.cache
org.eclipse.jetty
jetty maven插件
${jetty.plugin.version}
2.
瓦丁预释放
假的
瓦丁预释放
https://maven.vaadin.com/vaadin-prereleases
瓦丁快照
https://oss.sonatype.org/content/repositories/vaadin-snapshots/
假的
真的
瓦丁预释放
https://maven.vaadin.com/vaadin-prereleases
瓦丁快照
https://oss.sonatype.org/content/repositories/vaadin-snapshots/
假的
真的

我在新版本中有很多问题。所以，我现在转到旧版本

但是，我在图像布局上有错误。我如何解决这个问题？

有两件事：

在浏览器中，您正在访问

localhost:8080/从javascript调用java

，这与您定义的路由不匹配。当您在名为

Main

的视图上有

@Route

注释时，它将映射到根URL，因此请尝试仅使用

localhost:8080

访问它

我不确定您的

add

方法的用途，在该方法中，您抛出了一个

不支持操作异常

。我假设它是由您的IDE生成的，但是您正在扩展

垂直布局

，它已经有一个

add

方法，因此删除您的

add

方法版本

编辑以回答下一个问题

您最后的错误消息是

原因：java.lang.ClassCastException:com.example.MyImageSource无法转换为com.vaadin.flow.server.InputStreamFactory

您不能将

MyImageSource

强制转换为

InputStreamFactory

，因为它不是

InputStreamFactory

不过你可以做一个。你所要做的就是

将

扩展StreamSource

更改为

实现InputStreamFactory

将

public InputStream getStream（）

更改为

public InputStream createInputStream（）

---

我遵循了以上两件事。但是，它没有完成。我编辑了我的问题。编辑了我的答案

com.example.MyImageSource无法转换为com.vaadin.flow.server.InputStreamFactory

请注意，您链接的教程是针对vaadin 8的。streamresourceapi从那时起就发生了变化，根据您的代码片段，您正在使用vaadin10或更高版本。以下是与Vaadin 14对应文档的链接：您使用的是什么版本的Vaadin？