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oracle中讀寫blob字段的問題解析

LOB類型分為BLOB和CLOB兩種：BLOB即二進(jìn)制大型對像（Binary Large Object），適用于存貯非文本的字節(jié)流數(shù)據(jù)（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(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明通過JDBC操縱Oracle數(shù)據(jù)庫LOB類型字段的幾種情況。

先建立如下兩個測試用的數(shù)據(jù)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(shù)據(jù)庫中插入一個新的CLOB對像

復(fù)制代碼代碼如下:

public static void clobInsert(String infile) throws Exception
{
/* 設(shè)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對像 */
oracle.sql.CLOB clob = (oracle.sql.CLOB)rs.getClob("CLOBCOL");
/* 向CLOB對像中寫入數(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) {
/* 出錯回滾 */
conn.rollback();
throw ex;
}

/* 恢復(fù)原提交狀態(tài) */
conn.setAutoCommit(defaultCommit);
}

2、修改CLOB對像（是在原CLOB對像基礎(chǔ)上進(jìn)行覆蓋式的修改）

復(fù)制代碼代碼如下:

public static void clobModify(String infile) throws Exception
{
/* 設(shè)定不自動提交 */
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);

try {
/* 查詢CLOB對象并鎖定 */
ResultSet rs = stmt.executeQuery("SELECT CLOBCOL FROM TEST_CLOB WHERE ID='111' FOR UPDATE");
while (rs.next()) {
/* 獲取此CLOB對像 */
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) {
/* 出錯回滾 */
conn.rollback();
throw ex;
}

/* 恢復(fù)原提交狀態(tài) */
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）

復(fù)制代碼代碼如下:

public static void clobReplace(String infile) throws Exception
{
/* 設(shè)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對像 */
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) {
/* 出錯回滾 */
conn.rollback();
throw ex;
}

/* 恢復(fù)原提交狀態(tài) */
conn.setAutoCommit(defaultCommit);
}

4、CLOB對像讀取

復(fù)制代碼代碼如下:

public static void clobRead(String outfile) throws Exception
{
/* 設(shè)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(fù)原提交狀態(tài) */
conn.setAutoCommit(defaultCommit);
}

二、 BLOB對象的存取

1、向數(shù)據(jù)庫中插入一個新的BLOB對像

復(fù)制代碼代碼如下:

public static void blobInsert(String infile) throws Exception
{
/* 設(shè)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對像 */
oracle.sql.BLOB blob = (oracle.sql.BLOB)rs.getBlob("BLOBCOL");
/* 向BLOB對像中寫入數(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) {
/* 出錯回滾 */
conn.rollback();
throw ex;
}
/* 恢復(fù)原提交狀態(tài) */
conn.setAutoCommit(defaultCommit);
}

2、修改BLOB對像（是在原BLOB對像基礎(chǔ)上進(jìn)行覆蓋式的修改）

復(fù)制代碼代碼如下:

public static void blobModify(String infile) throws Exception
{
/* 設(shè)定不自動提交 */
boolean defaultCommit = conn.getAutoCommit();
conn.setAutoCommit(false);

try {
/* 查詢BLOB對象并鎖定 */
ResultSet rs = stmt.executeQuery("SELECT BLOBCOL FROM TEST_BLOB WHERE ID='222' FOR UPDATE");
while (rs.next()) {
/* 取出此BLOB對像 */
oracle.sql.BLOB blob = (oracle.sql.BLOB)rs.getBlob("BLOBCOL");
/* 向BLOB對像中寫入數(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) {
/* 出錯回滾 */
conn.rollback();
throw ex;
}

/* 恢復(fù)原提交狀態(tài) */
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）

復(fù)制代碼代碼如下:

public static void blobReplace(String infile) throws Exception
{
/* 設(shè)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對像 */
oracle.sql.BLOB blob = (oracle.sql.BLOB)rs.getBlob("BLOBCOL");
/* 向BLOB對像中寫入數(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) {
/* 出錯回滾 */
conn.rollback();
throw ex;
}

/* 恢復(fù)原提交狀態(tài) */
conn.setAutoCommit(defaultCommit);
}

4、BLOB對像讀取

復(fù)制代碼代碼如下:

public static void blobRead(String outfile) throws Exception
{
/* 設(shè)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(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，有下面幾個顯著不同的特點：

一是必須取消自動提交。

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