oracle中讀寫blob字段的問題
LOB類型分為BLOB和CLOB兩種：BLOB即二進制大型對像（Binary Large Object），適用於存貯非文本的字節流數據（如程序、圖像、影音等）。而CLOB，即字符型大型對像（Character Large Object），則與字符集相關，適於存貯文本型的數據（如歷史檔案、大部頭著作等）。
下面以程序實例說明通過JDBC操縱Oracle數據庫LOB類型字段的幾種情況。
先建立如下兩個測試用的數據庫表，Power Designer PD模型如下：
建表SQL語句為：
CREATE TABLE TEST_CLOB ( ID NUMBER(3), CLOBCOL CLOB)
CREATE TABLE TEST_BLOB ( ID NUMBER(3), BLOBCOL BLOB)
一、 CLOB對象的存取
1、往數據庫中插入一個新的CLOB對像
public static void clobInsert(String infile) throws Exception
{
/* 設定不自動提交 */
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);
try {
/* 插入一個空的CLOB對像 */
stmt.executeUpdate("INSERT INTO TEST_CLOB VALUES ('111', EMPTY_CLOB())");
/* 查詢此CLOB對象並鎖定 */
ResultSet rs = stmt.executeQuery("SELECT CLOBCOL FROM TEST_CLOB WHERE ID='111' FOR UPDATE");
while (rs.next()) {
/* 取出此CLOB對像 */
oracle.sql.CLOB clob = (oracle.sql.CLOB)rs.getClob("CLOBCOL");
/* 向CLOB對像中寫入數據 */
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) {
/* 出錯回滾 */
conn.rollback();
throw ex;
}
/* 恢復原提交狀態 */
conn.setAutoCommit(defaultCommit);
}
2、修改CLOB對像（是在原CLOB對像基礎上進行覆蓋式的修改）
public static void clobModify(String infile) throws Exception
{
/* 設定不自動提交 */
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);
try {
/* 查詢CLOB對象並鎖定 */
ResultSet rs = stmt.executeQuery("SELECT CLOBCOL FROM TEST_CLOB WHERE ID='111' FOR UPDATE");
while (rs.next()) {
/* 獲取此CLOB對像 */
oracle.sql.CLOB clob = (oracle.sql.CLOB)rs.getClob("CLOBCOL");
/* 進行覆蓋式修改 */
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) {
/* 出錯回滾 */
conn.rollback();
throw ex;
}
/* 恢復原提交狀態 */
conn.setAutoCommit(defaultCommit);
}
3、替換CLOB對像（將原CLOB對像清除，換成一個全新的CLOB對像）
public static void clobReplace(String infile) throws Exception
{
/* 設定不自動提交 */
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);
try {
/* 清空原CLOB對像 */
stmt.executeUpdate("UPDATE TEST_CLOB SET CLOBCOL=EMPTY_CLOB() WHERE ID='111'");
/* 查詢CLOB對象並鎖定 */
ResultSet rs = stmt.executeQuery("SELECT CLOBCOL FROM TEST_CLOB WHERE ID='111' FOR UPDATE");
while (rs.next()) {
/* 獲取此CLOB對像 */
oracle.sql.CLOB clob = (oracle.sql.CLOB)rs.getClob("CLOBCOL");
/* 更新數據 */
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) {
/* 出錯回滾 */
conn.rollback();
throw ex;
}
/* 恢復原提交狀態 */
conn.setAutoCommit(defaultCommit);
}
4、CLOB對像讀取
public static void clobRead(String outfile) throws Exception
{
/* 設定不自動提交 */
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);
try {
/* 查詢CLOB對像 */
ResultSet rs = stmt.executeQuery("SELECT * FROM TEST_CLOB WHERE ID='111'");
while (rs.next()) {
/* 獲取CLOB對像 */
oracle.sql.CLOB clob = (oracle.sql.CLOB)rs.getClob("CLOBCOL");
/* 以字符形式輸出 */
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;
}
/* 恢復原提交狀態 */
conn.setAutoCommit(defaultCommit);
}
二、 BLOB對象的存取
1、 向數據庫中插入一個新的BLOB對像
public static void blobInsert(String infile) throws Exception
{
/* 設定不自動提交 */
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);
try {
/* 插入一個空的BLOB對像 */
stmt.executeUpdate("INSERT INTO TEST_BLOB VALUES ('222', EMPTY_BLOB())");
/* 查詢此BLOB對象並鎖定 */
ResultSet rs = stmt.executeQuery("SELECT BLOBCOL FROM TEST_BLOB WHERE ID='222' FOR UPDATE");
while (rs.next()) {
/* 取出此BLOB對像 */
oracle.sql.BLOB blob = (oracle.sql.BLOB)rs.getBlob("BLOBCOL");
/* 向BLOB對像中寫入數據 */
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) {
/* 出錯回滾 */
conn.rollback();
throw ex;
}
/* 恢復原提交狀態 */
conn.setAutoCommit(defaultCommit);
}
2、修改BLOB對像（是在原BLOB對像基礎上進行覆蓋式的修改）
public static void blobModify(String infile) throws Exception
{
/* 設定不自動提交 */
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);
try {
/* 查詢BLOB對象並鎖定 */
ResultSet rs = stmt.executeQuery("SELECT BLOBCOL FROM TEST_BLOB WHERE ID='222' FOR UPDATE");
while (rs.next()) {
/* 取出此BLOB對像 */
oracle.sql.BLOB blob = (oracle.sql.BLOB)rs.getBlob("BLOBCOL");
/* 向BLOB對像中寫入數據 */
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) {
/* 出錯回滾 */
conn.rollback();
throw ex;
}
/* 恢復原提交狀態 */
conn.setAutoCommit(defaultCommit);
}
3、替換BLOB對像（將原BLOB對像清除，換成一個全新的BLOB對像）
public static void blobReplace(String infile) throws Exception
{
/* 設定不自動提交 */
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);
try {
/* 清空原BLOB對像 */
stmt.executeUpdate("UPDATE TEST_BLOB SET BLOBCOL=EMPTY_BLOB() WHERE ID='222'");
/* 查詢此BLOB對象並鎖定 */
ResultSet rs = stmt.executeQuery("SELECT BLOBCOL FROM TEST_BLOB WHERE ID='222' FOR UPDATE");
while (rs.next()) {
/* 取出此BLOB對像 */
oracle.sql.BLOB blob = (oracle.sql.BLOB)rs.getBlob("BLOBCOL");
/* 向BLOB對像中寫入數據 */
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) {
/* 出錯回滾 */
conn.rollback();
throw ex;
}
/* 恢復原提交狀態 */
conn.setAutoCommit(defaultCommit);
}
4、BLOB對像讀取
public static void blobRead(String outfile) throws Exception
{
/* 設定不自動提交 */
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);
try {
/* 查詢BLOB對像 */
ResultSet rs = stmt.executeQuery("SELECT BLOBCOL FROM TEST_BLOB WHERE ID='222'");
while (rs.next()) {
/* 取出此BLOB對像 */
oracle.sql.BLOB blob = (oracle.sql.BLOB)rs.getBlob("BLOBCOL");
/* 以二進制形式輸出 */
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) {
/* 出錯回滾 */
conn.rollback();
throw ex;
}
/* 恢復原提交狀態 */
conn.setAutoCommit(defaultCommit);
}
觀察上述程序對LOB類型字段的存取，我們可以看出，較之其它類型字段，有下面幾個顯著不同的特點：
一是必須取消自動提交。
