CLOB 字段读写

创建测试表

建表语句如下：

create table t_clob( 
        id varchar2(32) primary key, 
        clobfield CLOB 
); 

读取CLOB字段的代码示例

public void readClob() {  
    //自定义的数据库连接管理类　  
    Connection conn = DbManager.getInstance().getConnection();  
    try {  
        PreparedStatement stat = conn.prepareStatement("select clobfield from t_clob where id ='1'");  
        ResultSet rs = stat.executeQuery();  
        if (rs.next()) {  
            oracle.sql.CLOB clob = (oracle.sql.CLOB) rs.getClob("clobfield");  
            String value = clob.getSubString(1, (int) clob.length());  
            System.out.println("CLOB字段的值：" + value);  
        }  
        conn.commit();  
    } catch (SQLException e) {  
        e.printStackTrace();  
    } finally {
    	DbManager.getInstance().closeConnection(conn); 
	}
}  

写入CLOB字段的代码示例

public void writeClob() {  
    //自定义的数据库连接管理类　  
    Connection conn = DbManager.getInstance().getConnection();  
    try {  
        conn.setAutoCommit(false);  
        // 1.这种方法写入CLOB字段可以。  
        PreparedStatement stat = conn.prepareStatement("insert into t_clob (id, clobfield) values(sys_guid(), ?)");  
        String clobContent = "This is a very very long string";  
        StringReader reader = new StringReader(clobContent);  
        stat.setCharacterStream(1, reader, clobContent.length());  
        stat.executeUpdate();  
  
        // 2.使用类似的方法进行更新CLOB字段，则不能成功　  
        // stat.close();  
        // stat = null;  
        // stat = conn.prepareStatement("update t_clob set clobfield =? where id=1");  
        // stat.setCharacterStream(1, reader, clobContent.length());  
        // stat.executeUpdate();  
  
        // 3.需要使用for update方法来进行更新，  
        // 但是，特别需要注意，如果原来CLOB字段有值，需要使用empty_clob()将其清空。  
        // 如果原来是null，也不能更新，必须是empty_clob()返回的结果。  
        stat = conn.prepareStatement("select clobfield from t_clob where id='1' for update");  
        ResultSet rs = stat.executeQuery();  
        if (rs.next()) {  
            oracle.sql.CLOB clob = (oracle.sql.CLOB) rs.getClob("clobfield");  
            Writer outStream = clob.getCharacterOutputStream();  
            char[] c = clobContent.toCharArray();  
            outStream.write(c, 0, c.length);  
            outStream.flush();  
            outStream.close();  
        }  
        conn.commit();  
    } catch (SQLException | IOException e) {  
        // TODO Auto-generated catch block  
        e.printStackTrace();  
    }  
  
    DbManager.getInstance().closeConnection(conn);