试图显示从 MySQL 表中读取的图像

Question

我正在尝试从 MySQL 表中读取图像 该图像被定义为 longblob，我正在使用 Eclipse Juno（更新）、Java 和 GWT（最新版本）。但是，当我运行时，我在页面上收到错误消息（我的第一个视图没有显示）：

onModuleLoad() threw an exception


Exception while loading module org.AwardTracker.client.AwardTracker. See Development Mode for details.
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.google.gwt.dev.shell.ModuleSpace.onLoad(ModuleSpace.java:406)
at com.google.gwt.dev.shell.OophmSessionHandler.loadModule(OophmSessionHandler.java:200)
at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:526)
at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:364)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.RuntimeException: Deferred binding failed for 'org.AwardTracker.client.DBConnection' (did you forget to inherit a required module?)
at com.google.gwt.dev.shell.GWTBridgeImpl.create(GWTBridgeImpl.java:53)
at com.google.gwt.core.shared.GWT.create(GWT.java:57)
at com.google.gwt.core.client.GWT.create(GWT.java:85)
at org.AwardTracker.client.LoginView.<init>(LoginView.java:29)
at org.AwardTracker.client.AwardTracker.onModuleLoad(AwardTracker.java:14)
... 9 more
Caused by: com.google.gwt.core.ext.UnableToCompleteException: (see previous log entries)
at com.google.gwt.dev.shell.ModuleSpace.rebind(ModuleSpace.java:605)
at com.google.gwt.dev.shell.ModuleSpace.rebindAndCreate(ModuleSpace.java:465)
at com.google.gwt.dev.shell.GWTBridgeImpl.create(GWTBridgeImpl.java:49)
... 13 more

开发控制台有以下消息（前几行）：

[DEBUG] [org.AwardTracker.AwardTracker] - Validating units:
[INFO] [org.AwardTracker.AwardTracker] - Ignored 4 units with compilation errors in first pass.
Compile with -strict or with -logLevel set to TRACE or DEBUG to see all errors.
[ERROR] [org.AwardTracker.AwardTracker] - Errors in 'file:/C:/Users/Glyndwr/Eclipse/Workspace/AwardTracker/src/org/AwardTracker/client/DBConnection.java'
[ERROR] [org.AwardTracker.AwardTracker] - Line 15: No source code is available for type java.sql.Blob; did you forget to inherit a required module?

我的 DBConnection 是：

package org.AwardTracker.client;

import java.util.List;
import java.sql.Blob;

import com.google.gwt.user.client.rpc.RemoteService;

/**
 * The client side stub for the RPC service.
 */
public interface DBConnection extends RemoteService {
public User authenticateUser(String user, String pass, String level, String archived);
public User duplicateUser(String user, String pass, String level, String archived);
public User createUser(String user, String pass, String level, String archived);
public List<YouthMember> getYM(String id, String surname, String first_name, String dob, Blob image, String archived);
}

据此，我认为 java.sql.Blob 不能在 GWT 中使用。我应该使用什么？

我将图像存储在数据库中，而不是图像链接，因为我只有少量低分辨率图像要存储，因此数据库不应该因此而过度征税。

问候，

格林

我做了以下更改：

在 MySQLConnection 类的服务器端，我添加了以下方法（但是它有列出的错误）：

public String getImageData(String id){
    ResultSet result = null;
    PreparedStatement ps = null;
    String imageDataString = null;
    try {
        // Read in the image from the database.
        ps = conn.prepareStatement(
              "SELECT at_cub_details.cd_photograph " +
                      "FROM at_cub_details " + 
                      "WHERE at_cub_details.cd_id = \"" + id + "\"");
        result = ps.executeQuery();
        while (result.next()) {
            File file = new File(result.getString(1));
            FileInputStream imageInFile = new FileInputStream(file);
            byte imageData[] = new byte[(int) file.length()];
            imageInFile.read(imageData);

            //Convert Image byte array into Base64 String
            imageDataString = encodeImage(imageData);

            imageInFile.close();
        }

    }
    catch (FileNotFoundException e) {
        System.out.println("getImageData - Image not found" + e);
    } 
    catch (IOException ioe) {
        System.out.println("getImageData - Exception while reading the Image " + ioe);
    }
    catch (SQLException e) {
      //do stuff on fail
        System.out.println("SQLException getImageData 1.");
        e.printStackTrace();
        user = null;
    }
    finally {
        if (result != null) {
            try {
                result.close();
            }
            catch (SQLException e) {
                System.out.println("SQLException getImageData 2.");
                e.printStackTrace();
            }
        }
        if (ps != null) {
            try {
                ps.close();
            }   
            catch (SQLException e) {
                System.out.println("SQLException getImageData 3.");
                e.printStackTrace();
            }
        }
    }
    return imageDataString;
}
 /**
  * Encodes the byte array into base64 string
  * @param imageByteArray - byte array
  * @return String a {@link java.lang.String}
  */
public static String encodeImage(byte[] imageByteArray) {
    return Base64.encodeBase64URLSafeString(imageByteArray); [This line has the error: Multiple markers at this line
- The method encodeBase64URLSafeString(byte[]) is undefined for the 
 type Base64
- Line breakpoint:MySQLConnection [line: 287] - encodeImage(byte[]). However I have import org.apache.commons.codec.binary.Base64;]

}

在客户端我有：

public void renderYouthMemberTable(List<YouthMember> youthMemberList) {
    if (youthMemberList != null) {
        int row = 0;
        int col = 0;
        flexTable.clear();
        for (YouthMember youthMember : youthMemberList) {
            String id = youthMember.getId();

            String imageDataString = getImageData(); [ Error: The method getImageData() is undefined for the type SelectPersonView]

            // Converting a Base64 String into Image byte array
            byte[] imageByteArray = decodeImage(imageDataString);

            // Write a image byte array into file system
            FileOutputStream imageOutFile = new FileOutputStream(
                    "/Users/jeeva/Pictures/wallpapers/water-drop-after-convert.jpg");
            imageOutFile.write(imageByteArray);

            flexTable.setWidget(row, col, new Label(imageByteArray)); [Error: The constructor Label(byte[]) is undefined]
            //flexTable.setWidget(row, col, new Label(youthMember.getId()));
            flexTable.setWidget(row + 1, col, new Label(youthMember.getSurname() + ", " + youthMember.getFirstname()));

            //imageOutFile.close();

            col = col + 1;
            if (col > 7) {
                row = row + 2;
                col = 0;
            }
        }
    }

}

/**
 * Decodes the base64 string into byte array
 * @param imageDataString - a {@link java.lang.String}
 * @return byte array
 */
public static byte[] decodeImage(String imageDataString) {
    return Base64.decodeBase64(imageDataString); [ With the error: The method decodeBase64(byte[]) in the type Base64 is not applicable for the arguments (String)]
    }

我从http://www.myjeeva.com/2012/07/how-to-convert-image-to-string-and-string-to-image-in-java/复制了这段代码

问候，

格林

Answer 1

当您使用 GWT 时，不要忘记您的最终代码是 javascript。所以有些课程不可用。

但是：

-> GWT 中的图像可以有一个用于源 url 的 servlet url（带参数）。

-> 此处描述的其他方式：GWT - image from database：使用在回调时返回 base64 字符串 + 图像初始化的服务 rpc。

希望对你的问题有用。