.NET/Java PDF, Tiff, Barcode SDK Library

HttpApplication is the type that manages the request as it moves through the pipeline. Up to now we ve examined the events along that pipeline and the mechanisms at your disposal for extending its functionality. A critical step of that process is creating and executing the request handler. The Page handler, which is an instance of System.Web.UI.Page (or any type derived from that type), deals with ASPX pages. In this section we re going to take a look at what it takes to be a handler that the Framework recognizes, some of the other handlers that are built into the Framework, and how to create your own handlers to custom process specialized requests. So what does it take to be a handler How does the Framework know how deal with an instance of the Page class, a derived type that didn t exist at the time the Framework was compiled Via polymorphism, of course. The only thing the pipeline cares about is a simple interface named IHttpHandler. Any type that implements this interface qualifies to receive requests from the ASP .NET Framework and process them however it sees fit. Once a type implements this interface, it s associated with requests via any combination of file name, file extension, or request type. For example, the extension ASPX is mapped to the Page handler factory. The pipeline hands the request off to this type by calling a method on the IHttpHandler interface. This class looks at the request, creates an instance of the corresponding page object, and hands the request off to it via the same interface method, as shown in Figure 2-12.

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Summary

import book.util.Util; class DemoClobOperations { public static void main(String args[]) { Util.checkProgramUsage( args ); Connection conn = null; try { // following gets connection; sets autocommit to true conn = JDBCUtil.getConnection("benchmark", "benchmark", args[0]); We invoke the following five methods in the main() method: readClob(): Reads a CLOB value readClobInChunks(): Reads a CLOB value piecemeal writeClob(): Writes to a CLOB value, replacing the characters from the beginning writeClobInChunks(): Writes to a CLOB value piecemeal, replacing the characters from the beginning appendToClob(): Appends a string value to a CLOB At the end of the main() method, we commit the changes: _readClob( conn ); _readClobInChunks( conn ); _writeClob( conn ); _writeClobInChunks( conn ); _appendToClob( conn ); conn.commit(); } catch (Exception e) { JDBCUtil.printExceptionAndRollback(conn, e ); } finally { // release resources associated with JDBC in the finally clause. JDBCUtil.close( conn ); } } The following section explains the method _readClob() in the class DemoClobOperations.

The method _readClob() is explained here, with comments interspersed: /* demos how to read from a CLOB in the database.*/ private static void _readClob( Connection conn ) throws SQLException, IOException { PreparedStatement pstmt = null; ResultSet rset = null; BufferedReader reader = null; try { In the try catch block, we first declare our query string to select the CLOB column, following which we prepare the query statement: String stmtString = "select clob_col from clob_table "+ " where id = "; pstmt = conn.prepareStatement( stmtString ); Next, we bind the value of the column id to 1 (the length of the CLOB column in this row is 4,000 bytes). We execute the query and begin the standard ResultSet while loop: pstmt.setInt( 1, 1 ); rset = pstmt.executeQuery(); while( rset.next() ) { We use the method getClob() to get the CLOB object: Clob clob = rset.getClob( 1 ); Next, we get the data from the CLOB object using the getAsciiStream() method. We then read the stream data using the standard Java I/O method and print the number of characters read: reader = new BufferedReader ( new InputStreamReader ( clob.getAsciiStream() ) ); int numOfCharactersRead = 0; String line = null; while( (line = reader.readLine()) != null ) { //System.out.println( line ); numOfCharactersRead += line.length(); } System.out.println("num of characters read: " + numOfCharactersRead ); } } finally {

A few handlers are built into the ASP .NET 1.x versions of the Framework, and ASP .NET 2.0 adds quite a few more. Handlers can be used for any type of specialized request processing. They can be mapped to a specific URL (as is the case with trace.axd), or the can be mapped to a specific extension (as is the case with *.aspx). Handlers can also respond to specific HTTP request types (GET, POST, HEAD, and others). There actually is a handler that rejects outright any request type that is not a GET, POST, or HEAD (the HttpMethodNotAllowed handler). Table 2-4 is a list of the handlers built into the Framework and a brief description of the work that they do. A detailed discussion of some of the more prominent handlers follows. Table 2-4. Handlers Built into the ASP .NET Framework

In this chapter, you saw how the functional programming techniques from 3 are often used to implement in-memory queries similar to those used to access databases. You also saw how to use sequence expressions as an alternative notation for these query expressions. We then turned to databases themselves and covered how to use ADO.NET to access relational databases. You also saw how to perform a variety of database-related tasks from Visual Studio. You next saw how to perform simple, typed queries using F# LinqToSql, taking particular advantage of the object/relational data objects generated by the LINQ tool SqlMetal.exe. Finally, you saw how to use XML as a generic data format, partly by using functionality from the LINQ libraries. In the next chapter, we ll cover parsing techniques, including using the lexer and parser generator tools that come with the F# distribution.