Java 使用 Hibernate 以块的形式读取/写入 blob 数据
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Read/write blob data in chunks with Hibernate
提问by Atticus
Is there a way to read and write from a blobin chunks using Hibernate.
Right now I am getting OutOfmemoryExceptionbecause the whole blob data is loaded in memory into a byte[].
有没有办法blob使用Hibernate. 现在我得到了，OutOfmemoryException因为整个 blob 数据都加载到内存中的byte[].
To be more specific, let's say I want to save a large file into a database table called File.
更具体地说，假设我想将一个大文件保存到名为File.
public class File {
private byte[] data;
}
I open the file in a FileInputStream and then what?
How do I tell Hibernate that I need to stream the content and will not give the whole byte[]array at once?
Should I use Blobinstead of byte[]? Anyway how can I stream the content?
我在 FileInputStream 中打开文件，然后呢？我如何告诉 Hibernate 我需要流式传输内容并且不会立即提供整个byte[]数组？我应该使用Blob而不是byte[]吗？无论如何，我如何流式传输内容？
Regarding reading, is there a way I can tell hibernate that (besides the lazy loading it does) I need the blob to be loaded in chunks, so when I retrieve my Fileit should not give me OutOfMemoryException.
关于阅读，有没有一种方法可以告诉 hibernate（除了它所做的延迟加载之外）我需要将 blob 分块加载，因此当我检索File它时，它不应该给我OutOfMemoryException.
I am using:
我在用：
- Oracle 11.2.0.3.0
- Hibernate 4.2.3 Final
- Oracle Driver 11.2
- 甲骨文 11.2.0.3.0
- 休眠 4.2.3 最终版
- Oracle 驱动程序 11.2
采纳答案by Roy Six
If going the Blob route, have you tried using Hibernate's LobHelpercreateBlobmethod, which takes an InputStream? To create a Blob and persist to the database, you would supply the FileInputStream object and the number of bytes.
如果走 Blob 路线，您是否尝试过使用 Hibernate 的LobHelpercreateBlob方法，该方法采用InputStream? 要创建 Blob 并持久保存到数据库，您需要提供 FileInputStream 对象和字节数。
Your File bean/entity class could map the Blob like this (using JPA annotations):
您的 File bean/实体类可以像这样映射 Blob（使用 JPA 注释）：
@Lob
@Column(name = "DATA")
private Blob data;
// Getter and setter
And the business logic/data access class could create the Blob for your bean/entity object like this, taking care not to close the input stream before persisting to the database:
并且业务逻辑/数据访问类可以像这样为您的 bean/实体对象创建 Blob，注意不要在持久化到数据库之前关闭输入流：
FileInputStream fis = new FileInputStream(file);
Blob data = getSession().getLobHelper().createBlob(fis, file.length());
fileEntity.setData(data);
// Persist file entity object to database
To go the other way and read the Blob from the database as a stream in chunks, you could call the Blob's getBinaryStreammethod, giving you the InputStream and allowing you to set the buffer size later if needed:
反过来，从数据库中读取 Blob 作为块中的流，您可以调用 Blob 的getBinaryStream方法，为您提供 InputStream 并允许您稍后根据需要设置缓冲区大小：
InputStream is = fileEntity.getData().getBinaryStream();
Struts 2 has a convenient configuration available that can set the InputStream result's buffer size.
Struts 2有一个方便的配置，可以设置 InputStream 结果的缓冲区大小。
