[Feature][Connector-JDBC] Supprot read Oracle BLOB data as string instead of bytes

[yzeng1618]

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Description

The JDBC connector currently fails to properly preserve the original content when processing BLOB fields from Oracle databases. This issue is clearly demonstrated in the provided example:

In the Oracle source table (TEST_BLOB_TABLE), we have BLOB data with different content types:

• Row 1: Simple text "Hello, World!"

• Row 2: XML content

• Row 3: HTML content
  However, after synchronization to the Doris target table, all BLOB data is converted to Base64-encoded strings:

• Row 1: "SGVsbG8sIFdvcmxkIQ=="

• Row 2: "PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiPz4..."

• Row 3: "PCFET0NUWVBFIGh0bWw+PGh0bWwgc3R5bGU9Im92..."
  This transformation makes the data unusable in its original form. Users cannot directly work with the text, XML, or HTML content as they could in the source database. Instead, they would need to perform additional Base64 decoding steps to retrieve the original content.

Usage Scenario

This feature is essential for users who need to accurately transfer Oracle BLOB data to target systems while preserving the original content format. Specific scenarios include:

1. Data Migration Projects : When migrating databases containing BLOB fields with text, XML, HTML, or other structured content from Oracle to systems like Doris, users need the original content to remain usable.
2. Document Management Systems : Organizations storing documents (HTML, XML, JSON) in Oracle BLOB fields need to maintain the document structure during data synchronization.
3. Application Integration : When applications rely on specific data formats stored in BLOB fields, the integrity of these formats must be preserved during data transfer.
4. Data Analysis : Analysts working with structured data stored in BLOB fields need the original format for proper analysis rather than encoded strings.
   Without this feature, users must implement additional post-processing steps to decode and reconstruct the original data, significantly complicating their data pipelines.

Related issues

no

Are you willing to submit a PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct

[Copilot]

Pull Request Overview

This PR addresses the Oracle BLOB data preservation issue by introducing a new configuration option, HANDLE_BLOB_AS_STRING, to allow conditional conversion of BLOB data to a string rather than always converting to Base64‐encoded bytes. Key changes include:

• Adding new tests to verify both BYTE and STRING conversions for BLOB fields.
• Updating type conversion logic in OracleTypeConverter, OracleTypeMapper, and OracleDialect to conditionally use string conversion based on the HANDLE_BLOB_AS_STRING flag.
• Propagating the new configuration option through JdbcConnectionConfig, JdbcCatalogOptions, and related factory and loader classes.

Reviewed Changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
OracleTypeConverterTest.java	Added tests to verify BLOB conversion with and without string conversion enabled.
JdbcFieldTypeUtils.java	Introduced special handling for BLOB in getString to decode using UTF-8.
JdbcCatalogUtils.java, JdbcSourceFactory.java, OracleTypeMapper.java, OracleTypeConverter.java, OracleDialectFactory.java, OracleDialect.java	Updated constructors and mappings to pass through the HANDLE_BLOB_AS_STRING flag for proper BLOB handling.
JdbcDialectLoader.java, JdbcDialectFactory.java	Added overloads to accept JdbcConnectionConfig for consistent option propagation.
JdbcSourceConfig.java, JdbcOptions.java, JdbcConnectionConfig.java	Integrated the new HANDLE_BLOB_AS_STRING configuration at the source level.
OracleCatalogFactory.java, OracleCatalog.java, JdbcCatalogOptions.java	Updated catalog creation and options to include HANDLE_BLOB_AS_STRING.
OracleTypeUtils.java (connector-cdc)	Adjusted the call to OracleTypeConverter to explicitly disable BLOB to string conversion for CDC.

[Copilot]

The getString method unconditionally converts a java.sql.Blob to a UTF-8 string. Consider integrating a check against the HANDLE_BLOB_AS_STRING configuration so that the conversion happens only when explicitly enabled.

Suggested change

	java.sql.Blob blob = (java.sql.Blob) obj;
	try {
	byte[] bytes = blob.getBytes(1, (int) blob.length());
	return new String(bytes, java.nio.charset.StandardCharsets.UTF_8);
	} finally {
	blob.free();
	if (HANDLE_BLOB_AS_STRING) {
	java.sql.Blob blob = (java.sql.Blob) obj;
	try {
	byte[] bytes = blob.getBytes(1, (int) blob.length());
	return new String(bytes, java.nio.charset.StandardCharsets.UTF_8);
	} finally {
	blob.free();
	}
	} else {
	throw new SQLException("BLOB handling as string is disabled by configuration.");

[Hisoka-X]

+1

[yzeng1618]

I have made some attempts at modification. I found that it would require a lot of changes to other files and some logical adaptations. Moreover, there is a high likelihood of parameter passing errors. In order to maintain simplicity, I have removed this part of the content.

[Copilot]

[nitpick] Consider making the handleBlobAsString field private and providing accessor methods to ensure consistency with other configuration fields, improving encapsulation.

Suggested change

	public boolean handleBlobAsString = JdbcOptions.HANDLE_BLOB_AS_STRING.defaultValue();
	private boolean handleBlobAsString = JdbcOptions.HANDLE_BLOB_AS_STRING.defaultValue();
	public boolean isHandleBlobAsString() {
	return handleBlobAsString;
	}
	public void setHandleBlobAsString(boolean handleBlobAsString) {
	this.handleBlobAsString = handleBlobAsString;
	}

[Hisoka-X]

+1 for this. @yzeng1618

[yzeng1618]

It has been modified.

[Hisoka-X]

Please update the docs and e2e.