将BufferedInputStream转换为图像

  • Z时代
  • 2024-01-10
  • 分类：问答

我无法将我的Blob转换为缓冲图像，因此可以使用它。我从使用inputstream上传的数据库中得到了一个blob（jpg图像）。在我的数据库中，它存储为BufferedInputStream，我注意到了。我得到的Blob很好，它有一堆怪异的符号，并说它是jpg，所以图像必须很好。谁能发现我在做什么错？也许我将其转换为错误？在image

= ImageIO.read（new ByteArrayInputStream（data））; 图片返回null。

@GET
@Path("{id}")
 @Produces("image/*")
public Response post(@PathParam("id") String id) throws IOException {
    Connection con = connection();
    Blob blob = getPhoto(con);
    BufferedImage image = null;
    byte[] data = null;
    int blobLength = 0;
    try {
        blobLength = (int) blob.length();
        data = blob.getBytes(1, blobLength);
        image = ImageIO.read(new ByteArrayInputStream(data));
    //  ImageIO.write(image, "JPEG", new File("C:/Users/Nicolas/Desktop/image.jpg"));
    } catch (SQLException e2) {
        e2.printStackTrace();
    }
    return Response.ok(image).build();
}

我如何写入数据库

public void postPhoto(Connection con, InputStream uploadedInputStream){
String mySQL = "INSERT INTO photos (photo) values (?)";
PreparedStatement pStmt = con.prepareStatement(mySQL);
pStmt.setBlob(1, uploadedInputStream);
pStmt.execute();
}

我如何将文件发送到我的servlet

var fileInput = document.getElementById('file');
var file = fileInput.files[0];
var formData = new FormData();
formData.append("file", file);
var parameters="first="+firstName+"&last="+lastName+"&file="+file;
xmlhttp.open("post","http://localhost:8080/restService/api/submitinfo",true);
xmlhttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
xmlhttp.send(formData);

回答：

首先，先确认uploadedInputStream是有效图像，然后再使用将其写出来ImageIO.write。您始终可以使用ImageIO.read读回的图像并将其写回到ByteArrayInputStream;）

我使用H2数据库进行了快速测试。

我注意到了几件事。 Blob#length返回long，而Blob#getBytes期望则返回int，这可能意味着您正在截断字节流。

另外，从H2的文档来看，似乎Blob内容没有保存在内存中，因此我改用了getBinaryStream。

import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.sql.Blob;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
public class TestImageDatbase {
    private Connection con;
    public static void main(String[] args) {
        new TestImageDatbase();
    }
    public TestImageDatbase() {
        try {
            clearDatabase();
            saveImage();
            loadImage();
        } catch (ClassNotFoundException | SQLException | IOException exp) {
            exp.printStackTrace();
        }
    }
    protected Connection getConnection() throws ClassNotFoundException, SQLException {
        Class.forName("org.h2.Driver");
        return DriverManager.getConnection("jdbc:h2:d:\\Image", "sa", "");
    }
    protected void clearDatabase() throws IOException, ClassNotFoundException, SQLException {
        Connection con = null;
        PreparedStatement stmt = null;
        try {
            con = getConnection();
            System.out.println("Cleaning database");
            stmt = con.prepareStatement("delete from images");
            int updated = stmt.executeUpdate();
            System.out.println("Updated " + updated + " rows");
        } finally {
            try {
                stmt.close();
            } catch (Exception e) {
            }
            try {
                con.close();
            } catch (Exception e) {
            }
        }
    }
    protected void saveImage() throws IOException, ClassNotFoundException, SQLException {
        Connection con = null;
        PreparedStatement stmt = null;
        ByteArrayOutputStream baos = null;
        ByteArrayInputStream bais = null;
        try {
            baos = new ByteArrayOutputStream();
            File source = new File("/path/to/file");
            System.out.println("Source size = " + source.length());
            BufferedImage img = ImageIO.read(source);
            ImageIO.write(img, "png", baos);
            baos.close();
            bais = new ByteArrayInputStream(baos.toByteArray());
            con = getConnection();
            stmt = con.prepareStatement("insert into images (image) values (?)");
            stmt.setBinaryStream(1, bais);
            int updated = stmt.executeUpdate();
            System.out.println("Updated " + updated + " rows");
        } finally {
            try {
                bais.close();
            } catch (Exception e) {
            }
            try {
                baos.close();
            } catch (Exception e) {
            }
            try {
                stmt.close();
            } catch (Exception e) {
            }
            try {
                con.close();
            } catch (Exception e) {
            }
        }
    }
    protected void loadImage() throws IOException, ClassNotFoundException, SQLException {
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {
            con = getConnection();
            stmt = con.prepareStatement("select image from images");
            rs = stmt.executeQuery();
            while (rs.next()) {
                System.out.println("Getting blob");
                Blob blob = rs.getBlob(1);
                System.out.println("Reading image");
                BufferedImage img = ImageIO.read(blob.getBinaryStream());
                System.out.println("img = " + img);
                JOptionPane.showMessageDialog(null, new JScrollPane(new JLabel(new ImageIcon(img))));
            }
        } finally {
            try {
                rs.close();
            } catch (Exception e) {
            }
            try {
                stmt.close();
            } catch (Exception e) {
            }
            try {
                con.close();
            } catch (Exception e) {
            }
        }
    }
}

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