oracle中读写blob字段的问题

    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。
 
Trackback: http://tb.blog.csdn.net/TrackBack.aspx?PostId=1475385