oracle中读写blob字段的问题解析

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

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对像

try {
/* 插入一个空的CLOB对像 */
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对像 */
oracle.sql.CLOB clob = (oracle.sql.CLOB)rs.getClob("CLOBCOL");
/* 向CLOB对像中写入数据 */
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);
}
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2、修改CLOB对像（是在原CLOB对像基础上进行覆盖式的修改）

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对像 */
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);
}
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3、替换CLOB对像（将原CLOB对像清除，换成一个全新的CLOB对像）

try {
/* 清空原CLOB对像 */
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对像 */
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);
}
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4、CLOB对像读取

try {
/* 查询CLOB对像 */
ResultSet rs = stmt.executeQuery("SELECT * FROM TEST_CLOB WHERE ID='111'");
while (rs.next()) {
/* 获取CLOB对像 */
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);
}
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二、 BLOB对象的存取

1、 向数据库中插入一个新的BLOB对像

try {
/* 插入一个空的BLOB对像 */
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对像 */
oracle.sql.BLOB blob = (oracle.sql.BLOB)rs.getBlob("BLOBCOL");
/* 向BLOB对像中写入数据 */
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);
}
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2、修改BLOB对像（是在原BLOB对像基础上进行覆盖式的修改）

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对像 */
oracle.sql.BLOB blob = (oracle.sql.BLOB)rs.getBlob("BLOBCOL");
/* 向BLOB对像中写入数据 */
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);
}
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3、替换BLOB对像（将