Select a BLOB column from Oracle DB using mybatis

Question

I'm trying to retrieve the contents of a BLOB column from an Oracle Database using mybatis. There is a table 'Demo' that contains a column 'binfile' of type BLOB. I would like to select the BLOB column and display it as a byte array/raw binary data. I'm using a Oracle thin JDBC driver.

The query in the mybatis mapper looks like this:

<mapper namespace="Oracle" >
...
<select id="SelectBinary" resultType="hashmap">
    SELECT binfile from mpdemo.Demo
    </select>
</mapper>

If I do this, the result I get looks like this:

BINFILE: "oracle.sql.BLOB@5d67eb18"

If I do this:

<select id="SelectBinaryDup" resultType="hashmap">
  SELECT utl_raw.cast_to_varchar2(dbms_lob.substr(binfile)) from mpdemo.Demo
</select>

I obviously get an error saying that the raw variable saying 'PL/SQL: numeric or value error: raw variable length too long' as the image is well over 100 kB, since a VARCHAR2 variable in SQL can support only 2000 bytes.

Is there a solution to this?

I thought of writing a stored proc that reads the BLOB column block by block and writes the output to a file. But that file will be saved on the database server and I can't retrieve that.

Jarandinor · Accepted Answer · 2013-06-12T07:34:51.127

You can use the BLOB directly, do import oracle.sql.BLOB;

Examples:

BLOB blob = (BLOB)map.get("binfile");

//one way: as array
byte[] bytes = blob.getBytes(1L, (int)blob.length());
System.out.println(new String(bytes)); //use for text data
System.out.println(Arrays.toString(bytes));

//another way: as stream
BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("data.bin"));
InputStream is = blob.binaryStreamValue();
int b = -1;
while ((b = is.read()) != -1) {
    bos.write(b);
}
bos.close();

score 0 · Answer 2 · answered Jun 12 '13 at 10:31

0

Have you tried mapping the field to jdbcType=LONGVARBINARY?

answered Jun 12 '13 at 10:31

Ian Lim

4,164
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43

not working if mapping field to jdbcType=LONGVARBINARY – Ian Lim Dec 17 '18 at 03:26

score 0 · Answer 3 · edited May 23 '17 at 11:52

In my case I had to implement a custom BaseTypeHandler to support Oracle BLOB conversion to byte[] for Mybatis.

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: https://stackoverflow.com/a/27522590/2692914.

Select a BLOB column from Oracle DB using mybatis

3 Answers3