Question

我正在尝试使用mybatis从Oracle数据库中检索BLOB列的内容。有一个表'Demo'，其中包含BLOB类型的列'binfile'。我想选择BLOB列并将其显示为字节数组/原始二进制数据。我正在使用Oracle瘦JDBC驱动程序。

mybatis映射器中的查询如下所示：

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

如果我这样做，我得到的结果如下：

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

如果我这样做：

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

我显然得到一个错误，说原始变量说'PL / SQL：数字或值错误：原始变量长度太长'，因为图像远远超过100 kB，因为SQL中的VARCHAR2变量只能支持2000个字节

有解决方法吗？

我想过编写一个存储过程，它逐块读取BLOB列并将输出写入文件。但是该文件将保存在数据库服务器上，我无法检索它。

Answer 1

您可以直接使用BLOB，执行import oracle.sql.BLOB;

示例：

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();

Answer 2

您是否尝试将字段映射到jdbcType = LONGVARBINARY？

Answer 3

就我而言，我必须实施custom BaseTypeHandler to support Oracle BLOB conversion to byte[] for Mybatis。

将Oracle JDBC驱动程序添加到项目中，您也需要mybatis个依赖项。如果您使用的是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>

添加custom BaseTypeHandler for reading byte[] from Oracle BLOB类：

@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);
        }
    }
}

将类型处理程序包添加到mybatis配置中。如你所见，我正在使用spring-mybatis：

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <property name="dataSource" ref="dataSource" />
    <property name="typeHandlersPackage" value="package.where.customhandler.is" />
</bean>

然后，您可以从Mybatis 的Oracle BLOB中读取byte []：

public class Bean {
    private byte[] file;
}

interface class Dao {
    @Select("select file from some_table where id=#{id}")
    Bean getBean(@Param("id") String id);
}

我希望这会有所帮助。这是对这个出色答案的改编：https://stackoverflow.com/a/27522590/2692914。

使用mybatis从Oracle DB中选择BLOB列

3 个答案: