c# usb barcode reader example Updating an Existing CLOB Record in Font

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Updating an Existing CLOB Record
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Figure 8-30 shows the results of updating an existing CLOB record.
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Figure 8-30. Updating a CLOB using a servlet
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CHAPTER 8 READING AND WRITING CLOBS
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Viewing the Database Content After Insertion
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This shows the database after the insertion: mysql> select id, filename, filebody from datafiles where id=4000; +------+----------+---------------------------------------------- + | id | filename | filebody | +------+----------+-----------------------------------------------+ | 4000 | file40 | This is the first line of file500. | | | | This is the 2nd of file500. | | | | This is the end of file500. | +------+----------+-----------------------------------------------+ 1 row in set (0.00 sec) Using DisplayMySqlClobServlet, you can view the CLOB in a Web browser, as shown in Figure 8-31.
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Figure 8-31. Viewing an updated CLOB using a servlet
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Solution: UpdateMySqlClobServlet
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The MySQL solution is identical to the Oracle solution with the exception of the getConnection() method, which returns a MySQL Connection object. You can download the complete MySQL solution from the book s Web site. The following is getConnection() for the MySQL database: public static Connection getConnection() throws Exception { String driver = "org.gjt.mm.mysql.Driver"; String url = "jdbc:mysql://localhost/octopus"; String username = "root"; String password = "root"; Class.forName(driver); // load MySQL driver return DriverManager.getConnection(url, username, password); }
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8-16. How Do You Delete an Existing CLOB of an Oracle Database Using a Servlet
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The SQL DELETE statement deletes rows in a table. The simple syntax is as follows: DELETE FROM table_name WHERE column_name_1 = some_value_1 and Column_name_2 = some_value_2 and ... The goal is to delete an existing database record that has a CLOB column. You can do this by providing the primary key for the desired record (to be deleted). You may also delete the CLOB record using SQL s LIKE statement against the content of the CLOB (the body of the file), but this is not
CHAPTER 8 READING AND WRITING CLOBS
recommended. (Most databases will not allow you to index the CLOBs; for example, MySQL allows you to index portions of CLOBs.) For solving this problem, you will use the DataFiles table (the id column is the primary key, and fileBody is the CLOB column). The servlet interface is as follows: http://localhost:8000/octopus/servlet/DeleteClobFromOracleServlet id=<id> Therefore, DeleteClobFromMySqlServlet has only one parameter: id (the ID of CLOB, which is the primary key that identifies the record) To delete an existing record with the ID of 500, issue this: http://localhost:8000/octopus/servlet/DeleteClobFromOracleServlet id=500
Viewing the Database Content Before Deletion
This is the database before the deletion: SQL> desc DataFiles; Name Null --------------------- -------ID NOT NULL FILENAME FILEBODY Type -----------NUMBER(38) VARCHAR2(20) CLOB
SQL> select id, filename from dataFiles; ID ---------4000 1000 2000 500 FILENAME -------------------file4000 file1 file2 file500
Using a Servlet to Delete a Record (with CLOB)
Therefore, the servlet call is as follows: http://localhost:8000/octopus/servlet/DeleteClobFromOracleServlet id=500
Viewing the Actual Servlet Call for Deleting a Record (with CLOB)
Figure 8-32 shows the result of deleting a record.
Figure 8-32. Deleting a CLOB using a servlet
Viewing the Database Content After Deletion
This shows the database after the deletion:
CHAPTER 8 READING AND WRITING CLOBS
SQL> select id, filename from dataFiles; ID ---------4000 1000 2000 FILENAME -------------------file4000 file1 file2
Solution: DeleteClobFromOracleServlet
This shows the DeleteClobFromOracleServlet solution: import java.io.*; import java.sql.*; import javax.servlet.*; import javax.servlet.http.*; import jcb.db.DatabaseUtil; import jcb.util.IOUtil; public class DeleteClobFromOracleServlet extends HttpServlet { private static final String DELETE_CLOB_RECORD = "delete from DataFiles where id = "; public static Connection getConnection() throws Exception {...} public void doGet(...) {...} public void doPost(...) {...} }
getConnection()
This shows getConnection(): public static Connection getConnection() throws Exception { String driver = "oracle.jdbc.driver.OracleDriver"; String url = "jdbc:oracle:thin:@matrix:1521:caspian"; String username = "mp"; String password = "mp2"; Class.forName(driver); // load Oracle driver return DriverManager.getConnection(url, username, password); }
doGet()
This shows doGet(): public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { Connection conn = null; PreparedStatement pstmt = null; String id = request.getParameter("id").trim(); ServletOutputStream out = response.getOutputStream(); response.setContentType("text/html"); out.println("<html><head><title>Delete CLOB Record</title></head>");
CHAPTER 8 READING AND WRITING CLOBS
try { conn = getConnection(); pstmt = conn.prepareStatement(DELETE_CLOB_RECORD); pstmt.setString(1, id); pstmt.executeUpdate(); pstmt.executeUpdate(); out.println("<body><h4>deleted CLOB record with id=" +id+"</h4></body></html>"); } catch (Exception e) { out.println("<body><h4>Error="+e.getMessage()+"</h4></body></html>"); } finally { DatabaseUtil.close(pstmt); DatabaseUtil.close(conn); } }
doPost()
This shows doPost(): public void doPost( HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { doGet(request, response); }
8-17. How Do You Delete an Existing CLOB of an MySQL Database Using a Servlet
The goal is to delete an existing database record, which has a CLOB column. Basically, you can do this by providing the primary key for the desired record (to be deleted). For solving this problem, you will use the DataFiles table (the id column is the primary key, and fileBody is the CLOB column). The servlet interface is as follows: http://localhost:8000/octopus/servlet/DeleteClobFromMySqlServlet id=<id> Therefore, DeleteClobFromMySqlServlet has only one parameter: id (the ID of CLOB, which is the primary key that identifies the record) To delete an existing record with the ID of 500, you will issue the following servlet call: http://localhost:8000/octopus/servlet/DeleteClobFromMySqlServlet id=500
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