Java 如何使用JPA从PostgreSQL读取bytea图像数据？

我有PostgreSQL数据库，有数据类型为“bytea”的“image”列。我无法修改列或数据库配置。JPA注释的POJO包含以下映射

@Column(name="image")
private byte[] image;

返回的数据采用以下格式（这只是一个示例）

当我将这些数据写入文件（.jpeg）时，照片查看器会显示“这是损坏的文件”。我也知道实际的图像字节数据看起来和上面的示例不同。我读过一些博客，其中提到PostgreSQL将十六进制转换应用于bytea数据。如何将其恢复为原始数据（带或不带JPA）

数据库-PostgresSQL版本9.5.1

司机

<dependency>
    <groupId>org.postgresql</groupId>
    <artifactId>postgresql</artifactId>
    <version>9.4-1205-jdbc41</version>
</dependency>

org.postgresql
postgresql
9.4-1205-jdbc41

插入图像，您可以使用：

  //Get the Large Object Manager to perform operations with
    LargeObjectManager lobj = ((org.postgresql.PGConnection)conn).getLargeObjectAPI();

    // Create a new large object
    int oid = lobj.create(LargeObjectManager.READ | LargeObjectManager.WRITE);

    // Open the large object for writing
    LargeObject obj = lobj.open(oid, LargeObjectManager.WRITE);

    // Now open the file
    File file = new File("myimage.gif");
    FileInputStream fis = new FileInputStream(file);

    // Copy the data from the file to the large object
    byte buf[] = new byte[2048];
    int s, tl = 0;
    while ((s = fis.read(buf, 0, 2048)) > 0) {
        obj.write(buf, 0, s);
        tl += s;
    }

    // Close the large object
    obj.close();

// Now insert the row into imageslo
PreparedStatement ps = conn.prepareStatement("INSERT INTO imageslo VALUES (?, ?)");
ps.setString(1, file.getName());
ps.setInt(2, oid);
ps.executeUpdate();
ps.close();
fis.close();

// Finally, commit the transaction.
conn.commit();

// All LargeObject API calls must be within a transaction block
conn.setAutoCommit(false);

// Get the Large Object Manager to perform operations with
LargeObjectManager lobj = ((org.postgresql.PGConnection)conn).getLargeObjectAPI();

PreparedStatement ps = conn.prepareStatement("SELECT imgoid FROM imageslo WHERE imgname = ?");
ps.setString(1, "myimage.gif");
ResultSet rs = ps.executeQuery();
while (rs.next()) {
    // Open the large object for reading
    int oid = rs.getInt(1);
    LargeObject obj = lobj.open(oid, LargeObjectManager.READ);

    // Read the data
    byte buf[] = new byte[obj.size()];
    obj.read(buf, 0, obj.size());
    // Do something with the data read here

    // Close the object
    obj.close();
}
rs.close();
ps.close();

// Finally, commit the transaction.
conn.commit();

从大型对象检索图像：

  //Get the Large Object Manager to perform operations with
    LargeObjectManager lobj = ((org.postgresql.PGConnection)conn).getLargeObjectAPI();

    // Create a new large object
    int oid = lobj.create(LargeObjectManager.READ | LargeObjectManager.WRITE);

    // Open the large object for writing
    LargeObject obj = lobj.open(oid, LargeObjectManager.WRITE);

    // Now open the file
    File file = new File("myimage.gif");
    FileInputStream fis = new FileInputStream(file);

    // Copy the data from the file to the large object
    byte buf[] = new byte[2048];
    int s, tl = 0;
    while ((s = fis.read(buf, 0, 2048)) > 0) {
        obj.write(buf, 0, s);
        tl += s;
    }

    // Close the large object
    obj.close();

// Now insert the row into imageslo
PreparedStatement ps = conn.prepareStatement("INSERT INTO imageslo VALUES (?, ?)");
ps.setString(1, file.getName());
ps.setInt(2, oid);
ps.executeUpdate();
ps.close();
fis.close();

// Finally, commit the transaction.
conn.commit();

// All LargeObject API calls must be within a transaction block
conn.setAutoCommit(false);

// Get the Large Object Manager to perform operations with
LargeObjectManager lobj = ((org.postgresql.PGConnection)conn).getLargeObjectAPI();

PreparedStatement ps = conn.prepareStatement("SELECT imgoid FROM imageslo WHERE imgname = ?");
ps.setString(1, "myimage.gif");
ResultSet rs = ps.executeQuery();
while (rs.next()) {
    // Open the large object for reading
    int oid = rs.getInt(1);
    LargeObject obj = lobj.open(oid, LargeObjectManager.READ);

    // Read the data
    byte buf[] = new byte[obj.size()];
    obj.read(buf, 0, obj.size());
    // Do something with the data read here

    // Close the object
    obj.close();
}
rs.close();
ps.close();

// Finally, commit the transaction.
conn.commit();

---

返回的数据看起来像是base64编码的。在写入文件之前，必须将其解码回二进制数据

---

有关解码look的更多信息，请尝试使用

@Lob

@Lob
@Column(name="image")
private byte[] image;

如果您使用的是hibernate实现，那么也可以在列中添加

@Type（Type=“org.hibernate.Type.BinaryType”）

@Lob
@Column(name="image")
@Type(type="org.hibernate.type.BinaryType")
private byte[] image;

---

ImageEntity

package com.example;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class ImageEntity {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name="image")
    private byte[] image;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public byte[] getImage() {
        return image;
    }

    public void setImage(byte[] image) {
        this.image = image;
    }
}

package com.example;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface ImageRepository extends JpaRepository<ImageEntity, Long> {
}

ImageRepository

package com.example;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class ImageEntity {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name="image")
    private byte[] image;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public byte[] getImage() {
        return image;
    }

    public void setImage(byte[] image) {
        this.image = image;
    }
}

package com.example;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface ImageRepository extends JpaRepository<ImageEntity, Long> {
}

package.com.example；
导入org.springframework.data.jpa.repository.JpaRepository；
导入org.springframework.stereotype.Repository；
@存储库
公共接口ImageRepository扩展了JpaRepository{
}

测试

package com.example;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;

import javax.annotation.Resource;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.boot.test.SpringApplicationConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import junit.framework.TestCase;

@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = TestApplication.class)
public class ImageDaoTest {

    @Resource
    private ImageRepository imageRepository;

    @Test
    public void testImage() throws IOException {

        // Read an image from disk. Assume test.png exists
        ByteArrayOutputStream out = new ByteArrayOutputStream();

        try (InputStream in = getClass().getResourceAsStream("test.png")) {
            int length;
            byte[] buffer = new byte[1024];
            while ((length = in.read(buffer)) != -1) out.write(buffer, 0, length);
        }

        byte[] image = out.toByteArray();

        // Store image to DB
        ImageEntity imageEntiry = new ImageEntity();
        imageEntiry.setImage(image);
        long imageEntiryId = imageRepository.save(imageEntiry).getId();

        // Retrieve image from DB
        ImageEntity resultImageEntiry = imageRepository.findOne(imageEntiryId);
        byte[] resultImage = resultImageEntiry.getImage();

        // Compare retrieved image with source image by byte to byte comparison
        for (int i = 0; i < resultImage.length; i++) {
            TestCase.assertEquals(image[i], resultImage[i]);
        }

    }

}

package.com.example；
导入java.io.ByteArrayOutputStream；
导入java.io.IOException；
导入java.io.InputStream；
导入javax.annotation.Resource；
导入org.junit.Test；
导入org.junit.runner.RunWith；
导入org.springframework.boot.test.SpringApplicationConfiguration；
导入org.springframework.test.context.junit4.SpringJUnit4ClassRunner；
导入junit.framework.TestCase；
@RunWith（SpringJUnit4ClassRunner.class）
@SpringApplicationConfiguration（类=TestApplication.class）
公共类映像测试{
@资源
私有图像库；
@试验
public void testImage（）引发IOException{
//从磁盘读取图像。假设test.png存在
ByteArrayOutputStream out=新建ByteArrayOutputStream（）；
try（InputStream in=getClass（）.getResourceAsStream（“test.png”））{
整数长度；
字节[]缓冲区=新字节[1024]；
而（（长度=in.read（buffer））！=-1）out.write（buffer，0，length）；
}
byte[]image=out.toByteArray（）；
//将图像存储到数据库
ImageEntity ImageEntry=新的ImageEntity（）；
设置图像（图像）；
long-ImageEntryId=imageRepository.save（ImageEntry.getId（）；
//从数据库中检索图像
ImageEntity ResultimageEntry=imageRepository.findOne（ImageEntryId）；
字节[]resultImage=resultimageEntry.getImage（）；
//逐字节比较检索到的图像与源图像
for（int i=0；i

---

它适用于带有9.4.1207.jre7 jdbc驱动程序的Postgres 9.5.0-1。

我正在添加可能对其他人有用的完整代码（跳过try/catch）

---

我正在使用JPA，我不能做所有这些事情，比如回到JDBC。我认为此解决方案仍然无法处理十六进制编码的数据。

bytea

类型和大型对象在PostgreSQL中完全分离。您的示例应该可以工作（如果您不使用

@Lob

注释；请参阅）。你到底是怎么得到base64表示的？您确定这不是由视图相关服务输出（并可能转换）的内容吗？（请尝试调试

@实体

以查看

图像

属性的确切内容&在保存之前，您对该属性设置了什么）。您确定这是图像吗？你怎么储存它？另请检查。@pozs是用apache编解码器Base64类和javax.xml.bind.DatatypeConverter parseBase64Binary（）解码的。是的，您是对的，它的64Base ecoded。塔克斯。下面添加了完整的代码，可能对其他人有用。