How to Select a BLOB column from database using iB

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 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 2

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 3

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:

1. 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>
   

2. 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);
           }
       }
   }
   

3. 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>
   

4. 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.

Answer 4

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" />