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oracle中读写blob字段的问题解析

2019-01-03 Oracle 前端之家

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@H_301_0@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。

@H_301_0@先建立如下两个测试用的数据库表，Power Designer PD模型如下：

@H_301_0@建表sql语句为：
CREATE TABLE TEST_CLOB ( ID NUMBER(3),CLOBCOL CLOB)
CREATE TABLE TESTBLOB ( ID NUMBER(3),BLOBCOL BLOB)

@H3010@
一、 CLOB对象的存取

@H301_0@1、往数据库中插入一个新的CLOB对像

@H_301_0@<div class="codetitle"><a style="CURSOR: pointer" data="17852" class="copybut" id="copybut17852" onclick="doCopy('code17852')"> 代码如下:

<div class="codebody" id="code17852">
public static void clobInsert(String infile) throws Exception
{
/ 设定不自动提交 /
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);

@H_301_0@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;
}

@H_3010@/ 恢复原提交状态 /
conn.setAutoCommit(defaultCommit);
}

@H301_0@2、修改CLOB对像（是在原CLOB对像基础上进行覆盖式的修改）

@H_301_0@<div class="codetitle"><a style="CURSOR: pointer" data="9566" class="copybut" id="copybut9566" onclick="doCopy('code9566')"> 代码如下:

<div class="codebody" id="code9566">
public static void clobModify(String infile) throws Exception
{
/ 设定不自动提交 /
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);

@H_301_0@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;
}

@H_3010@/ 恢复原提交状态 /
conn.setAutoCommit(defaultCommit);
}

@H3010@3、替换CLOB对像（将原CLOB对像清除，换成一个全新的CLOB对像）

@H301_0@<div class="codetitle"><a style="CURSOR: pointer" data="87540" class="copybut" id="copybut87540" onclick="doCopy('code87540')"> 代码如下:

<div class="codebody" id="code87540">
public static void clobReplace(String infile) throws Exception
{
/ 设定不自动提交 /
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);

@H_301_0@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;
}

@H_3010@/ 恢复原提交状态 /
conn.setAutoCommit(defaultCommit);
}

@H3010@4、CLOB对像读取

@H301_0@<div class="codetitle"><a style="CURSOR: pointer" data="27061" class="copybut" id="copybut27061" onclick="doCopy('code27061')"> 代码如下:

<div class="codebody" id="code27061">
public static void clobRead(String outfile) throws Exception
{
/ 设定不自动提交 /
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);

@H_301_0@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;
}

@H_301_0@/ 恢复原提交状态 /
conn.setAutoCommit(defaultCommit);
}

@H_3010@
二、 BLOB对象的存取

@H301_0@1、向数据库中插入一个新的BLOB对像

@H_301_0@<div class="codetitle"><a style="CURSOR: pointer" data="8498" class="copybut" id="copybut8498" onclick="doCopy('code8498')"> 代码如下:<div class="codebody" id="code8498">
public static void blobInsert(String infile) throws Exception
{
/ 设定不自动提交 /
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);

@H_301_0@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);
}

@H_301_0@2、修改BLOB对像（是在原BLOB对像基础上进行覆盖式的修改）

@H_301_0@<div class="codetitle"><a style="CURSOR: pointer" data="90744" class="copybut" id="copybut90744" onclick="doCopy('code90744')"> 代码如下:<div class="codebody" id="code90744">
public static void blobModify(String infile) throws Exception
{
/ 设定不自动提交 /
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);

@H_301_0@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;
}

@H_301_0@/ 恢复原提交状态 /
conn.setAutoCommit(defaultCommit);
}

@H_3010@3、替换BLOB对像（将原BLOB对像清除，换成一个全新的BLOB对像）

@H301_0@<div class="codetitle"><a style="CURSOR: pointer" data="17447" class="copybut" id="copybut17447" onclick="doCopy('code17447')"> 代码如下:<div class="codebody" id="code17447">
public static void blobReplace(String infile) throws Exception
{
/ 设定不自动提交 /
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);

@H_301_0@try {
/ 清空原BLOB对像 /
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;
}

@H_301_0@/ 恢复原提交状态 /
conn.setAutoCommit(defaultCommit);
}

@H_3010@4、BLOB对像读取

@H301_0@<div class="codetitle"><a style="CURSOR: pointer" data="37337" class="copybut" id="copybut37337" onclick="doCopy('code37337')"> 代码如下:<div class="codebody" id="code37337">
public static void blobRead(String outfile) throws Exception
{
/ 设定不自动提交 /
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);

@H_301_0@try {
/ 查询BLOB对像 /
ResultSet rs = stmt.executeQuery("SELECT BLOBCOL FROM TEST_BLOB WHERE ID='222'");
while (rs.next()) {
/ 取出此BLOB对像 /
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;
}

@H_301_0@/ 恢复原提交状态 */
conn.setAutoCommit(defaultCommit);
}

观察上述程序对LOB类型字段的存取，我们可以看出，较之其它类型字段，有下面几个显著不同的特点：

@H_301_0@一是必须取消自动提交。

blob oracle oracle