oracle中读写blob字段的问题
2024-08-29 13:34:11
供稿：网友
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。
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