spring LobHandler 源码

spring LobHandler 代码

文件路径：/spring-jdbc/src/main/java/org/springframework/jdbc/support/lob/LobHandler.java

/*
 * Copyright 2002-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.jdbc.support.lob;

import java.io.InputStream;
import java.io.Reader;
import java.sql.ResultSet;
import java.sql.SQLException;

import org.springframework.lang.Nullable;

/**
 * Abstraction for handling large binary fields and large text fields in
 * specific databases, no matter if represented as simple types or Large OBjects.
 *
 * <p>Provides accessor methods for BLOBs and CLOBs, and acts as factory for
 * LobCreator instances, to be used as sessions for creating BLOBs or CLOBs.
 * LobCreators are typically instantiated for each statement execution or for
 * each transaction; they are not thread-safe because they might track
 * allocated database resources in order to free them after execution.
 *
 * <p>Most databases/drivers should be able to work with {@link DefaultLobHandler},
 * which by default delegates to JDBC's direct accessor methods, avoiding the
 * {@code java.sql.Blob} and {@code java.sql.Clob} API completely.
 * {@link DefaultLobHandler} can also be configured to access LOBs using
 * {@code PreparedStatement.setBlob/setClob} (e.g. for PostgreSQL), through
 * setting the {@link DefaultLobHandler#setWrapAsLob "wrapAsLob"} property.
 *
 * <p>Of course, you need to declare different field types for each database.
 * In Oracle, any binary content needs to go into a BLOB, and all character content
 * beyond 4000 bytes needs to go into a CLOB. In MySQL, there is no notion of a
 * CLOB type but rather a LONGTEXT type that behaves like a VARCHAR. For complete
 * portability, use a LobHandler for fields that might typically require LOBs on
 * some database because of the field size (take Oracle's numbers as a guideline).
 *
 * <p><b>Summarizing the recommended options (for actual LOB fields):</b>
 * <ul>
 * <li><b>JDBC 4.0 driver (including Oracle 11g driver):</b> Use {@link DefaultLobHandler},
 * potentially with {@code streamAsLob=true} if your database driver requires that
 * hint when populating a LOB field. Fall back to {@code createTemporaryLob=true}
 * if you happen to run into LOB size limitations with your (Oracle) database setup.
 * <li><b>Oracle 10g driver:</b> Use {@link DefaultLobHandler} with standard setup.
 * On Oracle 10.1, set the "SetBigStringTryClob" connection property; as of Oracle 10.2,
 * DefaultLobHandler should work with standard setup out of the box.
 * <li><b>PostgreSQL:</b> Configure {@link DefaultLobHandler} with {@code wrapAsLob=true},
 * and use that LobHandler to access OID columns (but not BYTEA) in your database tables.
 * <li>For all other database drivers (and for non-LOB fields that might potentially
 * turn into LOBs on some databases): Simply use a plain {@link DefaultLobHandler}.
 * </ul>
 *
 * @author Juergen Hoeller
 * @since 23.12.2003
 * @see DefaultLobHandler
 * @see java.sql.ResultSet#getBlob
 * @see java.sql.ResultSet#getClob
 * @see java.sql.ResultSet#getBytes
 * @see java.sql.ResultSet#getBinaryStream
 * @see java.sql.ResultSet#getString
 * @see java.sql.ResultSet#getAsciiStream
 * @see java.sql.ResultSet#getCharacterStream
 */
public interface LobHandler {

	/**
	 * Retrieve the given column as bytes from the given ResultSet.
	 * Might simply invoke {@code ResultSet.getBytes} or work with
	 * {@code ResultSet.getBlob}, depending on the database and driver.
	 * @param rs the ResultSet to retrieve the content from
	 * @param columnName the column name to use
	 * @return the content as byte array, or {@code null} in case of SQL NULL
	 * @throws SQLException if thrown by JDBC methods
	 * @see java.sql.ResultSet#getBytes
	 */
	@Nullable
	byte[] getBlobAsBytes(ResultSet rs, String columnName) throws SQLException;

	/**
	 * Retrieve the given column as bytes from the given ResultSet.
	 * Might simply invoke {@code ResultSet.getBytes} or work with
	 * {@code ResultSet.getBlob}, depending on the database and driver.
	 * @param rs the ResultSet to retrieve the content from
	 * @param columnIndex the column index to use
	 * @return the content as byte array, or {@code null} in case of SQL NULL
	 * @throws SQLException if thrown by JDBC methods
	 * @see java.sql.ResultSet#getBytes
	 */
	@Nullable
	byte[] getBlobAsBytes(ResultSet rs, int columnIndex) throws SQLException;

	/**
	 * Retrieve the given column as binary stream from the given ResultSet.
	 * Might simply invoke {@code ResultSet.getBinaryStream} or work with
	 * {@code ResultSet.getBlob}, depending on the database and driver.
	 * @param rs the ResultSet to retrieve the content from
	 * @param columnName the column name to use
	 * @return the content as binary stream, or {@code null} in case of SQL NULL
	 * @throws SQLException if thrown by JDBC methods
	 * @see java.sql.ResultSet#getBinaryStream
	 */
	@Nullable
	InputStream getBlobAsBinaryStream(ResultSet rs, String columnName) throws SQLException;

	/**
	 * Retrieve the given column as binary stream from the given ResultSet.
	 * Might simply invoke {@code ResultSet.getBinaryStream} or work with
	 * {@code ResultSet.getBlob}, depending on the database and driver.
	 * @param rs the ResultSet to retrieve the content from
	 * @param columnIndex the column index to use
	 * @return the content as binary stream, or {@code null} in case of SQL NULL
	 * @throws SQLException if thrown by JDBC methods
	 * @see java.sql.ResultSet#getBinaryStream
	 */
	@Nullable
	InputStream getBlobAsBinaryStream(ResultSet rs, int columnIndex) throws SQLException;

	/**
	 * Retrieve the given column as String from the given ResultSet.
	 * Might simply invoke {@code ResultSet.getString} or work with
	 * {@code ResultSet.getClob}, depending on the database and driver.
	 * @param rs the ResultSet to retrieve the content from
	 * @param columnName the column name to use
	 * @return the content as String, or {@code null} in case of SQL NULL
	 * @throws SQLException if thrown by JDBC methods
	 * @see java.sql.ResultSet#getString
	 */
	@Nullable
	String getClobAsString(ResultSet rs, String columnName) throws SQLException;

	/**
	 * Retrieve the given column as String from the given ResultSet.
	 * Might simply invoke {@code ResultSet.getString} or work with
	 * {@code ResultSet.getClob}, depending on the database and driver.
	 * @param rs the ResultSet to retrieve the content from
	 * @param columnIndex the column index to use
	 * @return the content as String, or {@code null} in case of SQL NULL
	 * @throws SQLException if thrown by JDBC methods
	 * @see java.sql.ResultSet#getString
	 */
	@Nullable
	String getClobAsString(ResultSet rs, int columnIndex) throws SQLException;

	/**
	 * Retrieve the given column as ASCII stream from the given ResultSet.
	 * Might simply invoke {@code ResultSet.getAsciiStream} or work with
	 * {@code ResultSet.getClob}, depending on the database and driver.
	 * @param rs the ResultSet to retrieve the content from
	 * @param columnName the column name to use
	 * @return the content as ASCII stream, or {@code null} in case of SQL NULL
	 * @throws SQLException if thrown by JDBC methods
	 * @see java.sql.ResultSet#getAsciiStream
	 */
	@Nullable
	InputStream getClobAsAsciiStream(ResultSet rs, String columnName) throws SQLException;

	/**
	 * Retrieve the given column as ASCII stream from the given ResultSet.
	 * Might simply invoke {@code ResultSet.getAsciiStream} or work with
	 * {@code ResultSet.getClob}, depending on the database and driver.
	 * @param rs the ResultSet to retrieve the content from
	 * @param columnIndex the column index to use
	 * @return the content as ASCII stream, or {@code null} in case of SQL NULL
	 * @throws SQLException if thrown by JDBC methods
	 * @see java.sql.ResultSet#getAsciiStream
	 */
	@Nullable
	InputStream getClobAsAsciiStream(ResultSet rs, int columnIndex) throws SQLException;

	/**
	 * Retrieve the given column as character stream from the given ResultSet.
	 * Might simply invoke {@code ResultSet.getCharacterStream} or work with
	 * {@code ResultSet.getClob}, depending on the database and driver.
	 * @param rs the ResultSet to retrieve the content from
	 * @param columnName the column name to use
	 * @return the content as character stream
	 * @throws SQLException if thrown by JDBC methods
	 * @see java.sql.ResultSet#getCharacterStream
	 */
	Reader getClobAsCharacterStream(ResultSet rs, String columnName) throws SQLException;

	/**
	 * Retrieve the given column as character stream from the given ResultSet.
	 * Might simply invoke {@code ResultSet.getCharacterStream} or work with
	 * {@code ResultSet.getClob}, depending on the database and driver.
	 * @param rs the ResultSet to retrieve the content from
	 * @param columnIndex the column index to use
	 * @return the content as character stream
	 * @throws SQLException if thrown by JDBC methods
	 * @see java.sql.ResultSet#getCharacterStream
	 */
	Reader getClobAsCharacterStream(ResultSet rs, int columnIndex) throws SQLException;

	/**
	 * Create a new {@link LobCreator} instance, i.e. a session for creating BLOBs
	 * and CLOBs. Needs to be closed after the created LOBs are not needed anymore -
	 * typically after statement execution or transaction completion.
	 * @return the new LobCreator instance
	 * @see LobCreator#close()
	 */
	LobCreator getLobCreator();

}

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