通過(guò)JDBC操縱Oracle數(shù)據(jù)庫(kù)LOB字段的幾種情況分析縱橫軟件制作中心 雨亦奇2003-6-10 15:14:19 在Oracle中，LOB（Large Object，大型對(duì)象）類型的字段現(xiàn)在用得越來(lái)越多了。因?yàn)檫@種類型的字段，容量大（最多能容納4GB的數(shù)據(jù)），且一個(gè)表中可以有多個(gè)這種類型的字段，很靈活，適用于數(shù)據(jù)量非常大的業(yè)務(wù)領(lǐng)域（如圖象、檔案等）。而LONG、LONG RAW等類型的字段，雖然存儲(chǔ)容量也不小（可達(dá)2GB），但由于一個(gè)表中只能有一個(gè)這樣類型的字段的限制，現(xiàn)在已很少使用了。 LOB類型分為BLOB和CLOB兩種：BLOB即二進(jìn)制大型對(duì)象（Binary Large Object），適用于存貯非文本的字節(jié)流數(shù)據(jù)（如程序、圖象、影音等）。而CLOB，即字符型大型對(duì)象（Character Large Object），則與字符集相關(guān)，適于存貯文本型的數(shù)據(jù)（如歷史檔案、大部頭著作等）。下面以程序?qū)嵗f(shuō)明通過(guò)JDBC操縱Oracle數(shù)據(jù)庫(kù)LOB類型字段的幾種情況。先建立如下兩個(gè)測(cè)試用的數(shù)據(jù)庫(kù)表，Power Designer PD模型如下：建表SQL語(yǔ)句為：CREATE TABLE TEST_CLOB ( ID NUMBER(3), CLOBCOL CLOB)CREATE TABLE TEST_BLOB ( ID NUMBER(3), BLOBCOL BLOB)一、 CLOB對(duì)象的存取1、往數(shù)據(jù)庫(kù)中插入一個(gè)新的CLOB對(duì)象public static void clobInsert(String infile) throws Exception{/* 設(shè)定不自動(dòng)提交 */boolean defaultCommit = conn.getAutoCommit();conn.setAutoCommit(false);try {/* 插入一個(gè)空的CLOB對(duì)象 */stmt.executeUpdate('INSERT INTO TEST_CLOB VALUES ('111', EMPTY_CLOB())');/* 查詢此CLOB對(duì)象并鎖定 */ResultSet rs = stmt.executeQuery('SELECT CLOBCOL FROM TEST_CLOB WHERE ID='111' FOR UPDATE');while (rs.next()) {/* 取出此CLOB對(duì)象 */oracle.sql.CLOB clob = (oracle.sql.CLOB)rs.getClob('CLOBCOL');/* 向CLOB對(duì)象中寫入數(shù)據(jù) */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(cuò)回滾 */conn.rollback();throw ex;}/* 恢復(fù)原提交狀態(tài) */conn.setAutoCommit(defaultCommit);}2、修改CLOB對(duì)象（是在原CLOB對(duì)象基礎(chǔ)上進(jìn)行覆蓋式的修改）public static void clobModify(String infile) throws Exception{/* 設(shè)定不自動(dòng)提交 */boolean defaultCommit = conn.getAutoCommit();conn.setAutoCommit(false);try {/* 查詢CLOB對(duì)象并鎖定 */ResultSet rs = stmt.executeQuery('SELECT CLOBCOL FROM TEST_CLOB WHERE ID='111' FOR UPDATE');while (rs.next()) {/* 獲取此CLOB對(duì)象 */oracle.sql.CLOB clob = (oracle.sql.CLOB)rs.getClob('CLOBCOL');/* 進(jìn)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(cuò)回滾 */conn.rollback();throw ex;}/* 恢復(fù)原提交狀態(tài) */conn.setAutoCommit(defaultCommit);} 3、替換CLOB對(duì)象（將原CLOB對(duì)象清除，換成一個(gè)全新的CLOB對(duì)象）public static void clobReplace(String infile) throws Exception{/* 設(shè)定不自動(dòng)提交 */boolean defaultCommit = conn.getAutoCommit();conn.setAutoCommit(false);try {/* 清空原CLOB對(duì)象 */stmt.executeUpdate('UPDATE TEST_CLOB SET CLOBCOL=EMPTY_CLOB() WHERE ID='111'');/* 查詢CLOB對(duì)象并鎖定 */ResultSet rs = stmt.executeQuery('SELECT CLOBCOL FROM TEST_CLOB WHERE ID='111' FOR UPDATE');while (rs.next()) {/* 獲取此CLOB對(duì)象 */oracle.sql.CLOB clob = (oracle.sql.CLOB)rs.getClob('CLOBCOL');/* 更新數(shù)據(jù) */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(cuò)回滾 */conn.rollback();throw ex;}/* 恢復(fù)原提交狀態(tài) */conn.setAutoCommit(defaultCommit);}4、CLOB對(duì)象讀取public static void clobRead(String outfile) throws Exception{/* 設(shè)定不自動(dòng)提交 */boolean defaultCommit = conn.getAutoCommit();conn.setAutoCommit(false);try {/* 查詢CLOB對(duì)象 */ResultSet rs = stmt.executeQuery('SELECT * FROM TEST_CLOB WHERE ID='111'');while (rs.next()) {/* 獲取CLOB對(duì)象 */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(fù)原提交狀態(tài) */conn.setAutoCommit(defaultCommit);}二、 BLOB對(duì)象的存取1、 向數(shù)據(jù)庫(kù)中插入一個(gè)新的BLOB對(duì)象public static void blobInsert(String infile) throws Exception{/* 設(shè)定不自動(dòng)提交 */boolean defaultCommit = conn.getAutoCommit();conn.setAutoCommit(false);try {/* 插入一個(gè)空的BLOB對(duì)象 */stmt.executeUpdate('INSERT INTO TEST_BLOB VALUES ('222', EMPTY_BLOB())');/* 查詢此BLOB對(duì)象并鎖定 */ResultSet rs = stmt.executeQuery('SELECT BLOBCOL FROM TEST_BLOB WHERE ID='222' FOR UPDATE');while (rs.next()) {/* 取出此BLOB對(duì)象 */oracle.sql.BLOB blob = (oracle.sql.BLOB)rs.getBlob('BLOBCOL');/* 向BLOB對(duì)象中寫入數(shù)據(jù) */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(cuò)回滾 */conn.rollback();throw ex;}/* 恢復(fù)原提交狀態(tài) */conn.setAutoCommit(defaultCommit);}2、修改BLOB對(duì)象（是在原BLOB對(duì)象基礎(chǔ)上進(jìn)行覆蓋式的修改）public static void blobModify(String infile) throws Exception{/* 設(shè)定不自動(dòng)提交 */boolean defaultCommit = conn.getAutoCommit();conn.setAutoCommit(false);try {/* 查詢BLOB對(duì)象并鎖定 */ResultSet rs = stmt.executeQuery('SELECT BLOBCOL FROM TEST_BLOB WHERE ID='222' FOR UPDATE');while (rs.next()) {/* 取出此BLOB對(duì)象 */oracle.sql.BLOB blob = (oracle.sql.BLOB)rs.getBlob('BLOBCOL');/* 向BLOB對(duì)象中寫入數(shù)據(jù) */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(cuò)回滾 */conn.rollback();throw ex;}/* 恢復(fù)原提交狀態(tài) */conn.setAutoCommit(defaultCommit);}3、替換BLOB對(duì)象（將原BLOB對(duì)象清除，換成一個(gè)全新的BLOB對(duì)象）public static void blobReplace(String infile) throws Exception{/* 設(shè)定不自動(dòng)提交 */boolean defaultCommit = conn.getAutoCommit();conn.setAutoCommit(false);try {/* 清空原BLOB對(duì)象 */stmt.executeUpdate('UPDATE TEST_BLOB SET BLOBCOL=EMPTY_BLOB() WHERE ID='222'');/* 查詢此BLOB對(duì)象并鎖定 */ResultSet rs = stmt.executeQuery('SELECT BLOBCOL FROM TEST_BLOB WHERE ID='222' FOR UPDATE');while (rs.next()) {/* 取出此BLOB對(duì)象 */oracle.sql.BLOB blob = (oracle.sql.BLOB)rs.getBlob('BLOBCOL');/* 向BLOB對(duì)象中寫入數(shù)據(jù) */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(cuò)回滾 */conn.rollback();throw ex;}/* 恢復(fù)原提交狀態(tài) */conn.setAutoCommit(defaultCommit);}4、BLOB對(duì)象讀取public static void blobRead(String outfile) throws Exception{/* 設(shè)定不自動(dòng)提交 */boolean defaultCommit = conn.getAutoCommit();conn.setAutoCommit(false);try {/* 查詢BLOB對(duì)象 */ResultSet rs = stmt.executeQuery('SELECT BLOBCOL FROM TEST_BLOB WHERE ID='222'');while (rs.next()) {/* 取出此BLOB對(duì)象 */oracle.sql.BLOB blob = (oracle.sql.BLOB)rs.getBlob('BLOBCOL');/* 以二進(jìn)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(cuò)回滾 */conn.rollback();throw ex;}/* 恢復(fù)原提交狀態(tài) */conn.setAutoCommit(defaultCommit);}觀察上述程序?qū)OB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(gè)顯著不同的特點(diǎn)：一是必須取消自動(dòng)提交。 存取操作開始前，必須用setAutoCommit(false)取消自動(dòng)提交。其它類型字段則無(wú)此非凡要求。這是因?yàn)榇嫒OB類型字段時(shí)，通常要進(jìn)行多次操作可以完成。不這樣的話，Oracle將拋出“讀取違反順序”的錯(cuò)誤。二是插入方式不同。LOB數(shù)據(jù)不能象其它類型數(shù)據(jù)一樣直接插入（INSERT）。插入前必須先插入一個(gè)空的LOB對(duì)象，CLOB類型的空對(duì)象為EMPTY_CLOB()，BLOB類型的空對(duì)象為EMPTY_BLOB()。之后通過(guò)SELECT命令查詢得到先前插入的記錄并鎖定，繼而將空對(duì)象修改為所要插入的LOB對(duì)象。三是修改方式不同。其它類型的字段修改時(shí)，用UPDATE … SET…命令即可。而LOB類型字段，則只能用SELECT … FOR UPDATE命令將記錄查詢出來(lái)并鎖定，然后才能修改。且修改也有兩種改法：一是在原數(shù)據(jù)基礎(chǔ)上的修改（即覆蓋式修改），執(zhí)行SELECT … FOR UPDATE后再改數(shù)據(jù)；二是替換（先將原數(shù)據(jù)清掉，再修改），先執(zhí)行UPDATE命令將LOB字段之值設(shè)為空的LOB對(duì)象，然后進(jìn)行第一種改法。建議使用替換的方法，以實(shí)現(xiàn)與其它字段UPDATE操作后一樣的效果。四是存取時(shí)應(yīng)使用由數(shù)據(jù)庫(kù)JDBC驅(qū)動(dòng)程序提供的LOB操作類。對(duì)于Oracle數(shù)據(jù)庫(kù)，應(yīng)使用oracle.sql.CLOB和oracle.sql.BLOB。不使用由數(shù)據(jù)庫(kù)JDBC驅(qū)動(dòng)程序提供的LOB類時(shí)，程序運(yùn)行時(shí)易于出現(xiàn)“抽象方法調(diào)用”的錯(cuò)誤，這是因?yàn)镴DBC所定義的Java.sql.Clob與java.sql.Blob接口，其中的一些方法并未在數(shù)據(jù)庫(kù)廠家提供的驅(qū)動(dòng)程序中真正實(shí)現(xiàn)。五是存取手段與文件操作相仿。對(duì)于BLOB類型，應(yīng)用InputStream/OutputStream類，此類不進(jìn)行編碼轉(zhuǎn)換，逐個(gè)字節(jié)存取。oracle.sql.BLOB類相應(yīng)提供了getBinaryStream()和getBinaryOutputStream()兩個(gè)方法，前一個(gè)方法用于讀取Oracle的BLOB字段，后一個(gè)方法用于將數(shù)據(jù)寫入Oracle的BLOB字段。對(duì)于CLOB類型，應(yīng)用Reader/Writer類，此類進(jìn)行編碼轉(zhuǎn)換。oracle.sql.CLOB類相應(yīng)提供了getCharacterStream()和getCharacterOutputStream()兩個(gè)方法，前一個(gè)方法用于讀取Oracle的CLOB字段，后一個(gè)方法用于將數(shù)據(jù)寫入Oracle的CLOB字段。需要說(shuō)明的是，為了大幅提高程序執(zhí)行效率，對(duì)BLOB/CLOB字段的讀寫操作，應(yīng)該使用緩沖操作類（帶Buffered前綴），即：BufferedInputStream，BufferedOutputStream，BufferedReader，BufferedWriter。例程中全部使用了緩沖操作類。小結(jié)：通過(guò)JDBC操縱Oracle數(shù)據(jù)庫(kù)的LOB字段，不外乎插入、修改、替換、讀取四種方式，把握起來(lái)并不難。在實(shí)際操作中要注重上面所說(shuō)的幾點(diǎn)，結(jié)合閱讀例程源程序，用戶會(huì)很快明白LOB類型字段的使用的，也必將領(lǐng)悟到這種類型字段的妙處！源文件下載>>（網(wǎng)頁(yè)編輯：編程浪子）