java - 从 mysql 数据库中检索图像时引发异常

Question

我想以二进制格式存储图像并以二进制格式检索它并以图像格式显示它。我能够以二进制格式存储文件，但是在检索它时出现错误 java 空指针异常。请指出错误。这是代码：

import java.awt.Image;
import java.awt.Toolkit;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class InsertImageTest {
int len;
    /**
     * This is used to get the Connection
     * 
     * @return
     */
    public Connection getConnection() {
        Connection connection = null;
        Statement stmt = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection(
                    "jdbc:mysql://localhost:3306/test", "root", "spanwave");
        } catch (Exception e) {
            System.out.println("Error Occured While Getting the Connection: - "
                    + e);
        }
        return connection;
    }

    /**
     * Insert Image
     */
     public Image getImageFile(String fileName) throws Exception {
InsertImageTest ins= new InsertImageTest();
Connection con=ins.getConnection();
Statement stmt=con.createStatement();
          //  String baseName=StoreImage.getBaseName(fileName);
            ResultSet rs=stmt.executeQuery("select * from trn_imgs where img_title='"+"Honda Car"+"'");
            if (!rs.next()) {
              System.out.println("Image:"+"honda car"+" not found");
              return null;
            }
           // int len=rs.getInt(2);

            byte [] b=new byte[len];
            InputStream in = rs.getBinaryStream(3);
            int n=in.read(b);
            System.out.println("n: "+n);
            in.close();
            Image img=Toolkit.getDefaultToolkit().createImage(b);
            System.out.println("Image: "+"honda car"+" retrieved ok, size: "+len);
            return img;
          }
    public void insertImage() throws IOException {
        Connection connection = null;
        PreparedStatement statement = null;
        FileInputStream inputStream = null;

        try {
            File image = new File("calender.png");
            inputStream = new FileInputStream(image);
            len=inputStream.available();
            connection = getConnection();
            statement = connection
                    .prepareStatement("insert into trn_imgs(img_title, img_data) "
                            + "values(?,?)");
            statement.setString(1, "Honda Car");
            statement.setBinaryStream(2, (InputStream) inputStream,
                    (int) (image.length()));

            statement.executeUpdate();
        } catch (FileNotFoundException e) {
            System.out.println("FileNotFoundException: - " + e);
        } catch (SQLException e) {
            System.out.println("SQLException: - " + e);
        } finally {
            try {
                connection.close();
                statement.close();
            } catch (SQLException e) {
                System.out.println("SQLException Finally: - " + e);
            }
        }

    }

    /***
     * Execute Program
     * 
     * @param args
     * @throws Exception 
     */
    public static void main(String[] args) throws Exception {
        InsertImageTest imageTest = new InsertImageTest();
        imageTest.insertImage();
    Image img=  imageTest.getImageFile("calender.png");
    }

}

Answer 1

除非您的代码中缺少某些内容：

 Statement stmt = null;
      //  String baseName=StoreImage.getBaseName(fileName);
        ResultSet rs=stmt.executeQuery("select * from trn_imgs where

 //stmt is null, right?

Answer 2

connection = getConnection();
 Statement stmt = connection.createStatement();
 ResultSet rs=stmt.executeQuery("select * from trn_imgs where img_title='"+"Honda Car"+"'");