Simple .NET/ASP.NET PDF document editor web control SDK

When you create an instance of a COM component, you obtain a pointer to an IUnknown interface that acts as the entry point to all interfaces implemented by the component The QueryInterface method of this interface allows you to get pointers to additional interfaces Interface pointers in COM are pointers to tables of pointers defining the method s location The program must know the layout of the table in order to read the desired pointer and invoke the corresponding method This knowledge can be compiled into the program (interfaces.

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The following DemoImplicitCaching program, along with the explanatory comments, illustrates the concept of implicit caching: /* * This program demonstrates implicit statement caching. * COMPATIBLITY NOTE: * runs successfully against and */ import java.sql.SQLException; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.CallableStatement; import oracle.jdbc.OracleConnection; import oracle.jdbc.OracleTypes; import book.util.JDBCUtil; import book.util.Util; class DemoImplicitCaching { public static void main(String args[]) throws SQLException { Util.checkProgramUsage( args ); OracleConnection conn = null; try { // get connection conn = (OracleConnection) JDBCUtil.getConnection("benchmark", "benchmark", args[0]); We print out the flag that indicates whether or not caching is enabled and the cache size (by default caching is disabled): System.out.println("implicit caching enabled: " + conn.getImplicitCachingEnabled() ); System.out.println("cache size: " + conn.getStatementCacheSize() ); Next we start the SQL trace: JDBCUtil.startTrace( conn ); We invoke the method _doSelect() in a for loop 1,000 times. The method itself will be explained shortly. for( int i=0; i < 1000; i++ ) { _doSelect ( conn, "/*+ implicit disabled */" ); }

The Page object happily aggregates all the rendered HTML as this recursive descent of the control tree transpires, and when all of the controls have made their contributions, the Page returns the rendered HTML to IIS as the response stream Along the way, any state information that controls might need when a postback occurs is squirreled away in the ViewState (unless, of course, ViewState is turned off for that control)..

1. Languages targeting .NET are not affected by these interoperability issues since they share the same CLR runtime.

We invoke the same loop again after enabling implicit caching and setting the statement cache size to a positive number (10 in this case): conn.setImplicitCachingEnabled( true ); conn.setStatementCacheSize( 10 ); System.out.println("implicit caching enabled: " + conn.getImplicitCachingEnabled() ); System.out.println("cache size: " + conn.getStatementCacheSize() ); for( int i=0; i < 1000; i++ ) { _doSelect ( conn, "/*+ implicit enabled */" ); } We demonstrate the concept of implicit caching for a CallableStatement by invoking the method _doExecuteCallableStatement(): // demonstrating use of implicit caching with callable statement for( int i=0; i < 1000; i++ ) { _doExecuteCallableStatement( conn, "/*+ enabled implicit caching for callable statement */" ); } } finally { // release resources associated with JDBC in the finally clause. JDBCUtil.close( conn ); } } The method _doSelect() mentioned previously is as follows: private static void _doSelect( Connection conn, String tag ) throws SQLException { PreparedStatement pstmt = null; ResultSet rset = null; The main point to note is that we tag the SQL string so that we can easily recognize it in the tkprof output. The rest of the code is a simple execution of the query using the PreparedStatement interface: String stmtString = "select " + tag + " count(*) from dual"; try { pstmt = conn.prepareStatement( stmtString ); rset = pstmt.executeQuery(); } finally {

The rendered size and contribution to the ViewState can be seen on the Trace output report. You can see this report simply by adding trace=true to the Page directive at the top of your ASPX file, as shown in Figure 3-14.

must be known at compile time) or acquired at run time by accessing component metadata in the form of an interface named IDispatch or a database called type library Since COM components can be compiled by any compiler supporting the generation of memory layouts compatible with the standard, it is necessary that the client shares the same layout for data structures that must be passed or returned by the component methods The standard type system for COM, defined in oledll, defines a simple and restricted set of types COM types correspond to the Variant type of Visual Basic and provide only basic types and arrays For structured types, COM requires a custom marshaller to be developed, but this has been rarely used in components that are widely available The COM infrastructure provides a memory manager that uses reference counting to automatically free components when they are not used anymore.

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