java.sql.SQLException:结果集开始之前[重复]
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【中文标题】java.sql.SQLException:结果集开始之前[重复]【英文标题】:java.sql.SQLException: Before start of result set [duplicate] 【发布时间】:2012-02-08 05:17:48 【问题描述】:我已尝试使用以下代码检索存储在数据库中的图像。我创建了一个名为image_db
的数据库,其中包含一个名为image_details
的表。该表有两个字段,id
和image_path
,两者都是mediumblob
类型。我在image_path
字段中存储了一些图像作为二进制文件。现在我想检索并显示它。
package cbir.imageAddition;
import java.awt.Image;
import java.awt.Toolkit;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.*;
enter code here
public class ImageRetrieve
public ImageRetrieve() throws SQLException, IOException, ClassNotFoundException
Connection con = null;
Statement st = null;
ResultSet rs = null;
String url = "jdbc:mysql://localhost:3306/";
String db = "image_db";
String driver = "com.mysql.jdbc.Driver";
String user = "root";
String pass = "root";
Class.forName(driver);
con = DriverManager.getConnection(url + db, user, pass);
//System.out.println("Connection url : "+url + db);
st = con.createStatement();
String sql = "select image_path from image_details where id=1";
rs = st.executeQuery(sql);
InputStream stream = rs.getBinaryStream(2);
ByteArrayOutputStream output = new ByteArrayOutputStream();
int a1 = stream.read();
while (a1 >= 0)
output.write((char) a1);
a1 = stream.read();
Image myImage = Toolkit.getDefaultToolkit().createImage(output.toByteArray());
output.close();
运行上述代码时出现以下异常:
awtJan 12, 2012 12:55:48 AM cbir.imageAddition.add_image_window jButton5ActionPerformed
SEVERE: null
java.sql.SQLException: Before start of result set
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1073)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:987)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:982)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:927)
at com.mysql.jdbc.ResultSetImpl.checkRowPos(ResultSetImpl.java:841)
at com.mysql.jdbc.ResultSetImpl.getStringInternal(ResultSetImpl.java:5650)
at com.mysql.jdbc.ResultSetImpl.getString(ResultSetImpl.java:5570)
at com.mysql.jdbc.ResultSetImpl.getString(ResultSetImpl.java:5610)
at cbir.imageAddition.ImageRetrieve.<init>(ImageRetrieve.java:49)
at cbir.imageAddition.add_image_window.jButton5ActionPerformed(add_image_window.java:280)
at cbir.imageAddition.add_image_window.access$400(add_image_window.java:26)
at cbir.imageAddition.add_image_window$5.actionPerformed(add_image_window.java:89)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6504)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6269)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4860)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4686)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2713)
at java.awt.Component.dispatchEvent(Component.java:4686)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:707)
at java.awt.EventQueue.access$000(EventQueue.java:101)
at java.awt.EventQueue$3.run(EventQueue.java:666)
at java.awt.EventQueue$3.run(EventQueue.java:664)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:680)
at java.awt.EventQueue$4.run(EventQueue.java:678)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:677)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
at java..EventDispatchThread.run(EventDispatchThread.java:90)
这是怎么引起的,我该如何解决?
【问题讨论】:
【参考方案1】:您必须调用 rs.next()(并检查它是否返回 true)才能访问结果集的第一行:
if (rs.next()
InputStream stream = rs.getBinaryStream(1);
...
也不是索引应该是 1,因为您的查询只选择一列。
我也不明白将 int 转换为 char 的意义。该方法将 int 作为参数。转换为字节至少是合乎逻辑的,但字节和字符在 Java 中不是一回事。
【讨论】:
感谢@JB Nizet。它起作用了。但我使用不同的方法来读取和显示图像: 我使用 ResultSet.getBytes() 方法读取图像和 'Image img = Toolkit.getDefaultToolkit().createImage(imagedata);'创建图像的方法。然后我使用新框架通过 setPreferedSize 方法将其大小设置为图像大小来显示图像。现在我想将存储在数据库中的图像显示为画廊。有什么方便的方法这样做???【参考方案2】:如果您执行选择查询,您将获得一个 ResultSet 对象。遍历它,你不会得到这个异常。
ResultSet rs = null;
rs = statement.executeQuery("select UUID_BINARY()");
if(rs.next())
newTripUUID = rs.getBytes(1);
【讨论】:
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