BLOB和CLOB的存取操作

LOB类型分为BLOB和CLOB两种：BLOB即二进制大型对象（Binary Large Object），适用于存贮非文本的字节流数据（如程序、图象、影音等）。而CLOB，即字符型大型对象（Character Large Object），则与字符集相关，适于存贮文本型的数据（如历史档案、大部头著作等）。

下面以程序实例说明通过JDBC操纵Oracle数据库LOB类型字段的几种情况。

先建立如下两个测试用的数据库表，Power Designer PD模型如下：

[img]http://www.csdn.net/Develop/ArticleImages/18/155/CSDN_Dev_Image_2003-6-111028171.jpg[/img] 建表SQL语句为：

CREATE TABLE TEST_CLOB ( ID NUMBER(3), CLOBCOL CLOB) CREATE TABLE TEST_BLOB ( ID NUMBER(3), BLOBCOL BLOB)

一、 CLOB对象的存取

1、往数据库中插入一个新的CLOB对象

public static void clobInsert(String infile) throws Exception {

/* 设定不自动提交 */

boolean defaultCommit = conn.getAutoCommit();

conn.setAutoCommit(false);

try {

/* 插入一个空的CLOB对象 */

stmt.executeUpdate(\"INSERT INTO TEST_CLOB VALUES ('111', EMPTY_CLOB())\");

/* 查询此CLOB对象并锁定 */

ResultSet rs = stmt.executeQuery(\"SELECT CLOBCOL FROM TEST_CLOB WHERE ID='111' FOR UPDATE\"); while (rs.next()) { /* 取出此CLOB对象 */

oracle.sql.CLOB clob = (oracle.sql.CLOB)rs.getClob(\"CLOBCOL\"); /* 向CLOB对象中写入数据 */

BufferedWriter out = new

BufferedWriter(clob.getCharacterOutputStream());

BufferedReader in = new BufferedReader(new FileReader(infile)); int c;

while ((c=in.read())!=-1) { out.write(c); }

in.close(); out.close(); }

/* 正式提交 */ conn.commit();

} catch (Exception ex) { /* 出错回滚 */ conn.rollback(); throw ex; }

/* 恢复原提交状态 */

conn.setAutoCommit(defaultCommit); }

2、修改CLOB对象（是在原CLOB对象基础上进行覆盖式的修改）

public static void clobModify(String infile) throws Exception {

/* 设定不自动提交 */

boolean defaultCommit = conn.getAutoCommit(); conn.setAutoCommit(false);

try {

/* 查询CLOB对象并锁定 */

ResultSet rs = stmt.executeQuery(\"SELECT CLOBCOL FROM TEST_CLOB WHERE ID='111' FOR UPDATE\"); while (rs.next()) { /* 获取此CLOB对象 */

oracle.sql.CLOB clob = (oracle.sql.CLOB)rs.getClob(\"CLOBCOL\");

/* 进行覆盖式修改 */

BufferedWriter out = new

BufferedWriter(clob.getCharacterOutputStream());

BufferedReader in = new BufferedReader(new FileReader(infile)); int c;

while ((c=in.read())!=-1) { out.write(c); }

in.close(); out.close(); }

/* 正式提交 */ conn.commit();

} catch (Exception ex) { /* 出错回滚 */ conn.rollback(); throw ex; }

/* 恢复原提交状态 */

conn.setAutoCommit(defaultCommit); }

3、替换CLOB对象（将原CLOB对象清除，换成一个全新的CLOB对象）

public static void clobReplace(String infile) throws Exception {

/* 设定不自动提交 */

boolean defaultCommit = conn.getAutoCommit(); conn.setAutoCommit(false);

try {

/* 清空原CLOB对象 */

stmt.executeUpdate(\"UPDATE TEST_CLOB SET CLOBCOL=EMPTY_CLOB() WHERE ID='111'\");

/* 查询CLOB对象并锁定 */

ResultSet rs = stmt.executeQuery(\"SELECT CLOBCOL FROM TEST_CLOB WHERE ID='111' FOR UPDATE\"); while (rs.next()) { /* 获取此CLOB对象 */

oracle.sql.CLOB clob = (oracle.sql.CLOB)rs.getClob(\"CLOBCOL\"); /* 更新数据 */

BufferedWriter out = new

BufferedWriter(clob.getCharacterOutputStream());

BufferedReader in = new BufferedReader(new FileReader(infile)); int c;

while ((c=in.read())!=-1) { out.write(c); }

in.close();

out.close(); }

/* 正式提交 */ conn.commit();

} catch (Exception ex) { /* 出错回滚 */ conn.rollback(); throw ex; }

/* 恢复原提交状态 */

conn.setAutoCommit(defaultCommit); }

4、CLOB对象读取

public static void clobRead(String outfile) throws Exception {

/* 设定不自动提交 */

boolean defaultCommit = conn.getAutoCommit(); conn.setAutoCommit(false);

try {

/* 查询CLOB对象 */

ResultSet rs = stmt.executeQuery(\"SELECT * FROM TEST_CLOB WHERE

ID='111'\");

while (rs.next()) { /* 获取CLOB对象 */

oracle.sql.CLOB clob = (oracle.sql.CLOB)rs.getClob(\"CLOBCOL\"); /* 以字符形式输出 */

BufferedReader in = new BufferedReader(clob.getCharacterStream()); BufferedWriter out = new BufferedWriter(new FileWriter(outfile)); int c;

while ((c=in.read())!=-1) { out.write(c); }

out.close(); in.close(); }

} catch (Exception ex) { conn.rollback(); throw ex; }

/* 恢复原提交状态 */

conn.setAutoCommit(defaultCommit); }

二、 BLOB对象的存取

1、 向数据库中插入一个新的BLOB对象

public static void blobInsert(String infile) throws Exception {

/* 设定不自动提交 */

boolean defaultCommit = conn.getAutoCommit(); conn.setAutoCommit(false);

try {

/* 插入一个空的BLOB对象 */

stmt.executeUpdate(\"INSERT INTO TEST_BLOB VALUES ('222', EMPTY_BLOB())\");

/* 查询此BLOB对象并锁定 */

ResultSet rs = stmt.executeQuery(\"SELECT BLOBCOL FROM TEST_BLOB WHERE ID='222' FOR UPDATE\"); while (rs.next()) { /* 取出此BLOB对象 */

oracle.sql.BLOB blob = (oracle.sql.BLOB)rs.getBlob(\"BLOBCOL\"); /* 向BLOB对象中写入数据 */

BufferedOutputStream out = new

BufferedOutputStream(blob.getBinaryOutputStream()); BufferedInputStream in = new BufferedInputStream(new FileInputStream(infile)); int c;

while ((c=in.read())!=-1) {

out.write(c); }

in.close(); out.close(); }

/* 正式提交 */ conn.commit();

} catch (Exception ex) { /* 出错回滚 */ conn.rollback(); throw ex; }

/* 恢复原提交状态 */

conn.setAutoCommit(defaultCommit); }

2、修改BLOB对象（是在原BLOB对象基础上进行覆盖式的修改）

public static void blobModify(String infile) throws Exception {

/* 设定不自动提交 */

boolean defaultCommit = conn.getAutoCommit(); conn.setAutoCommit(false);

try {

/* 查询BLOB对象并锁定 */

ResultSet rs = stmt.executeQuery(\"SELECT BLOBCOL FROM TEST_BLOB WHERE ID='222' FOR UPDATE\"); while (rs.next()) { /* 取出此BLOB对象 */

oracle.sql.BLOB blob = (oracle.sql.BLOB)rs.getBlob(\"BLOBCOL\"); /* 向BLOB对象中写入数据 */

BufferedOutputStream out = new

BufferedOutputStream(blob.getBinaryOutputStream()); BufferedInputStream in = new BufferedInputStream(new FileInputStream(infile)); int c;

while ((c=in.read())!=-1) { out.write(c); }

in.close(); out.close(); }

/* 正式提交 */ conn.commit();

} catch (Exception ex) { /* 出错回滚 */ conn.rollback();

throw ex; }

/* 恢复原提交状态 */

conn.setAutoCommit(defaultCommit); }

3、替换BLOB对象（将原BLOB对象清除，换成一个全新的BLOB对象）

public static void blobReplace(String infile) throws Exception {

/* 设定不自动提交 */

boolean defaultCommit = conn.getAutoCommit(); conn.setAutoCommit(false);

try {

/* 清空原BLOB对象 */

stmt.executeUpdate(\"UPDATE TEST_BLOB SET BLOBCOL=EMPTY_BLOB() WHERE ID='222'\");

/* 查询此BLOB对象并锁定 */

ResultSet rs = stmt.executeQuery(\"SELECT BLOBCOL FROM TEST_BLOB WHERE ID='222' FOR UPDATE\"); while (rs.next()) { /* 取出此BLOB对象 */

oracle.sql.BLOB blob = (oracle.sql.BLOB)rs.getBlob(\"BLOBCOL\"); /* 向BLOB对象中写入数据 */

BufferedOutputStream out = new

BufferedOutputStream(blob.getBinaryOutputStream()); BufferedInputStream in = new BufferedInputStream(new FileInputStream(infile)); int c;

while ((c=in.read())!=-1) { out.write(c); }

in.close(); out.close(); }

/* 正式提交 */ conn.commit();

} catch (Exception ex) { /* 出错回滚 */ conn.rollback(); throw ex; }

/* 恢复原提交状态 */

conn.setAutoCommit(defaultCommit); }

4、BLOB对象读取

public static void blobRead(String outfile) throws Exception {

/* 设定不自动提交 */

boolean defaultCommit = conn.getAutoCommit(); conn.setAutoCommit(false);

try {

/* 查询BLOB对象 */

ResultSet rs = stmt.executeQuery(\"SELECT BLOBCOL FROM TEST_BLOB WHERE ID='222'\");

while (rs.next()) { /* 取出此BLOB对象 */

oracle.sql.BLOB blob = (oracle.sql.BLOB)rs.getBlob(\"BLOBCOL\"); /* 以二进制形式输出 */

BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(outfile));

BufferedInputStream in = new

BufferedInputStream(blob.getBinaryStream()); int c;

while ((c=in.read())!=-1) { out.write(c); }

in.close(); out.close(); }

/* 正式提交 */ conn.commit();

} catch (Exception ex) { /* 出错回滚 */ conn.rollback(); throw ex; }

/* 恢复原提交状态 */

conn.setAutoCommit(defaultCommit); }