How to Select a BLOB column from database using iBatis - oracle

Question

One of a table's column is of BLOB datatype (Oracle 10g). We have a simple select query executed via iBatis to select the BLOB column and display it using Struts2 & JSP.
The result tag in the iBatis xml file had the jdbctype as java.sql.Blob
<result property="uploadContent" column="uploadcontent" jdbctype="Blob"/>
Should we be mentioning any typeHandler class for Blob column ? Currently we are getting an error stating column type mismatch.
Note: This column is selected and mapped into a java bean who has an attribute of type java.sql.Blob

Answer 1

I think you cannot use native jdbctype for LOB types in Oracle with iBatis. The solution is to create custom typeHandler to handle LOB and then map it like -
<result property="aClassStringProperty" column="aClobColumn" typeHandler="com.path.to.my.ClobTypeHandler"/>
More information on typeHandlerCallback here.

Answer 2

It is not neccesary to create a typeHandler. For Oracle, the jdbctype is BLOB
<result property="bytes" column="COLUMNBLOB" jdbcType="BLOB" />
Assumming "bytes" as byte [].
The important thing: in the select sql, you must set the jdbcType in this way:
INSERT INTO X (COLUMNBLOB) VALUES #bytes:BLOB#
I noticed that this jdbctype for Postgresql is different. You must set:
<result property="bytes" column="COLUMNBLOB" jdbcType="BINARY" />

Answer 3

I found somebody who deal with this here.
For a CLOB :
<result property="uploadContent" column="obfile" jdbctype="String" />
For a BLOB :
<result property="uploadContent" column="obfile" jdbctype="byte[]" />
I am still looking for it to work with C# !

Answer 4

I dindn't have problems using INSERTs, my problems where when I did SELECT of the blob type. I am using Oracle 9i and this is how I've done:
Add the Oracle JDBC driver to your project, you will need mybatis dependencies too. If you are using Maven:
<dependency>
<groupId>com.oracle</groupId>
<artifactId>ojdbc14</artifactId>
<version>10.2.0.3.0</version>
</dependency>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis-spring</artifactId>
<version>1.2.1</version>
</dependency>
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.2.3</version>
</dependency>
Add the custom BaseTypeHandler for reading byte[] from Oracle BLOB class:
#MappedTypes(byte[].class)
public class OracleBlobTypeHandler extends BaseTypeHandler<byte[]> {
#Override
public void setNonNullParameter(PreparedStatement preparedStatement, int i, byte[] bytes, JdbcType jdbcType) throws SQLException {
// see setBlobAsBytes method from https://jira.spring.io/secure/attachment/11851/OracleLobHandler.java
try {
if (bytes != null) {
//prepareLob
BLOB blob = BLOB.createTemporary(preparedStatement.getConnection(), true, BLOB.DURATION_SESSION);
//callback.populateLob
OutputStream os = blob.getBinaryOutputStream();
try {
os.write(bytes);
} catch (Exception e) {
throw new SQLException(e);
} finally {
try {
os.close();
} catch (Exception e) {
e.printStackTrace();//ignore
}
}
preparedStatement.setBlob(i, blob);
} else {
preparedStatement.setBlob(i, (Blob) null);
}
} catch (Exception e) {
throw new SQLException(e);
}
}
/** see getBlobAsBytes method from https://jira.spring.io/secure/attachment/11851/OracleLobHandler.java */
private byte[] getBlobAsBytes(BLOB blob) throws SQLException {
//initializeResourcesBeforeRead
if(!blob.isTemporary()) {
blob.open(BLOB.MODE_READONLY);
}
//read
byte[] bytes = blob.getBytes(1L, (int)blob.length());
//releaseResourcesAfterRead
if(blob.isTemporary()) {
blob.freeTemporary();
} else if(blob.isOpen()) {
blob.close();
}
return bytes;
}
#Override
public byte[] getNullableResult(ResultSet resultSet, String columnName) throws SQLException {
try {
//use a custom oracle.sql.BLOB
BLOB blob = (BLOB) resultSet.getBlob(columnName);
return getBlobAsBytes(blob);
} catch (Exception e) {
throw new SQLException(e);
}
}
#Override
public byte[] getNullableResult(ResultSet resultSet, int i) throws SQLException {
try {
//use a custom oracle.sql.BLOB
BLOB blob = (BLOB) resultSet.getBlob(i);
return getBlobAsBytes(blob);
} catch (Exception e) {
throw new SQLException(e);
}
}
#Override
public byte[] getNullableResult(CallableStatement callableStatement, int i) throws SQLException {
try {
//use a custom oracle.sql.BLOB
BLOB blob = (BLOB) callableStatement.getBlob(i);
return getBlobAsBytes(blob);
} catch (Exception e) {
throw new SQLException(e);
}
}
}
Add the type handlers package to mybatis configuration. As you can see, I am using spring-mybatis:
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<property name="dataSource" ref="dataSource" />
<property name="typeHandlersPackage" value="package.where.customhandler.is" />
</bean>
And then, you can read byte[] from Oracle BLOBs from Mybatis:
public class Bean {
private byte[] file;
}
interface class Dao {
#Select("select file from some_table where id=#{id}")
Bean getBean(#Param("id") String id);
}
I hope this will help.
This is an adaptation of this excellent answer: This is an adaptation of this excellent answer: https://stackoverflow.com/a/27522590/2692914.