Trying to display an image read from a MySQL table

Question

I am trying to read an image from a MySQL table The image is defined as a longblob and I am using Eclipse Juno (updated), Java, and GWT (latest version). However, when I run I get error messages on the page (my first view is not displayed):

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

The Development Console has the following messages (first few lines):

[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?

My DBConnection is:

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);
}

From this I take it that java.sql.Blob can not be used in GWT. What should I use?

I am storing the images in the database, rather than links to images, as I only have a small number of low resolution images to store so the database should not be over tax by this.

Regards,

Glyn

I have made the following changes:

On the server side in the class MySQLConnection I have added the following method (however it has the listed errors):

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;]

}

On the client side I have:

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)]
    }

I copied this code from: http://www.myjeeva.com/2012/07/how-to-convert-image-to-string-and-string-to-image-in-java/

Regards,

Glyn

Answer 1

When you use GWT, don't forget that your final code is javascript. So some classes are not availables.

But:

-> Images in GWT can have a servlet url for source url (with parameters).

-> other way described here: GWT - image from database : use a service rpc that return base64 string + image initialization on callback.

hope is usefull for your problem.