用 Java 写入新的 Blob
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Writing to a new Blob in Java
提问by Benjadette
I want to be able to create a new Blob object and then write to it. Originally, my general plan for this was as follows:
我希望能够创建一个新的 Blob 对象，然后写入它。本来，我对此的总体计划如下：
Create a new blob (null, because there's no Blob constructor) Create a new OutputStream and set it to blob.setBinaryStream(0) Write to the output stream.
创建一个新的 blob（null，因为没有 Blob 构造函数） 创建一个新的 OutputStream 并将其设置为 blob.setBinaryStream(0) 写入输出流。
However, I get a NullPointerException when I try to execute this code. Is there a different way I should be going about this? Any help would be appreciated.
但是，当我尝试执行此代码时，出现 NullPointerException。我应该采取不同的方式来解决这个问题吗？任何帮助，将不胜感激。
Thanks!
谢谢！
~B
~B
回答by Howard
java.sql.Blobis an interface and not a class, thus no constructor can exist. But you can instantiate the implementing class SerialBlobwhich allows you to construct a blob from a byte array.
java.sql.Blob是接口而不是类，因此不能存在构造函数。但是您可以实例化实现类SerialBlob，该类允许您从字节数组构造一个 blob。
回答by Jesper
Create a new blob (null, because there's no Blob constructor) Create a new OutputStream and set it to blob.setBinaryStream(0) Write to the output stream.
However, I get a NullPointerException when I try to execute this code.
创建一个新的 blob（null，因为没有 Blob 构造函数） 创建一个新的 OutputStream 并将其设置为 blob.setBinaryStream(0) 写入输出流。
但是，当我尝试执行此代码时，出现 NullPointerException。
Yes, that's not a surprise - you will get a NullPointerExceptionwhen you try to call a method on a variable that is null(as is your blobvariable).
是的，这并不奇怪 -NullPointerException当您尝试调用一个变量的方法时，您会得到一个null（就像您的blob变量一样）。
You should call setBinaryStreamon your PreparedStatementobject instead. Suppose that you have the data in a byte[], then you could do something like this:
你应该调用setBinaryStream你的PreparedStatement对象。假设您在 a 中有数据byte[]，那么您可以执行以下操作：
byte[] data = ...;
PreparedStatement ps = connection.prepareStatement(...);
ByteArrayInputStream stream = new ByteArrayInputStream(data);
ps.setBinaryStream(1, stream);
ps.executeUpdate();
回答by Ted Hopp
If you want to use the Blob in a CallableStatement or a PreparedStatement, you don't actually need to create a Blob object itself. The setBlobmethods come in flavors that take an InputStream in place of a Blob object. You could, for instance, write to a ByteArrayOutputStream, retrieve the byte array, and then wrap that in a ByteArrayInputStream. Or you could use piped streams.
如果您想在 CallableStatement 或 PreparedStatement 中使用 Blob，您实际上不需要创建 Blob 对象本身。这些setBlob方法具有使用 InputStream 代替 Blob 对象的风格。例如，您可以写入 ByteArrayOutputStream，检索字节数组，然后将其包装在 ByteArrayInputStream 中。或者您可以使用管道流。
