Because there can be so many variations in rowsets, the first part of this chapter gives a conceptual description of rowsets and their uses. The next part walks you through creating and using a rowset. Because a RowSet object follows the JavaBeansTM model for properties and event notification, it is a JavaBeans component that can be combined with other components in an application.
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As is true with other Beans, application programmers will probably use a development tool to create a RowSet object and set its properties. Rowsets may have many different implementations to fill different needs. These implementations fall into two broad categories, rowsets that are connected and those that are disconnected. A disconnected rowset gets a connection to a data source in order to fill itself with data or to propagate changes in data back to the data source, but most of the time it does not have a connection open.
Thus a rowset is an ideal format for sending data over a network to a thin client. Because it is not continually connected to its data source, a disconnected rowset stores its data in memory.
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It needs to maintain metadata about the columns it contains and information about its internal state. It also needs a facility for making connections, for executing commands, and for reading and writing data to and from the data source. A connected rowset, by contrast, opens a connection and keeps it open for as long as the rowset is in use. Although anyone can implement a rowset, most implementations will probably be provided by vendors offering RowSet classes designed for fairly specific purposes.
The following list of planned implementations gives you an idea of some of the possibilities. It can also depend on which properties have been set. The example rowsets used in this chapter are based on the CachedRowSet implementation, but because they are used for different purposes, one has several properties set whereas the other has none. Among other things, this tutorial will show you which properties to use and when to use them. Getting back to our owner of The Coffee Break chain, he has had one of his developers write an application that lets him project the effects of changing different coffee prices.
To create this application, the developer hooked together various JavaBeans components, setting their properties to customize them for his application. The first JavaBeans component, called Projector, was one that the owner bought from an economic forecasting firm.
This Bean takes all kinds of factors into account to project future revenues. Given the price and past sales performance of a coffee, it predicts the revenue the coffee is likely to generate and displays the results as a bar chart. The owner wants to be able to look at different coffee pricing scenarios using his laptop, so the application is set up such that it creates a rowset that can be copied to the laptop's disc.
The owner can later fire up the application on his laptop so that he can make updates to the rowset to test out various pricing strategies. The third Bean is a form for displaying and updating ResultSet objects. The application has a graphical user interface that includes buttons for opening and closing the application. These buttons are themselves JavaBeans components that the programmer assembled to make the GUI for his application. While he is at work, the owner can click on the form's New Data button to get a rowset filled with data. This is the work that requires the rowset to get a connection to the data source, execute its query, get a result set, and populate itself with the result set data.
When this work is done, the rowset disconnects itself.
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The owner can now click on the Close button to save the disconnected rowset to his laptop's disc. At home or on a plane, the owner can open the application on his laptop and click the button Open to copy the rowset from disc and start making updates using the form. The form displays the rowset, and he simply uses arrow keys or tabs to highlight the piece of data he wants to update.
He uses the editing component of the form to type in new values, and the Projector Bean shows the effects of the new values in its bar chart. When he gets back to headquarters, the owner can copy his updated rowset to his office computer if he wants to propagate the updates back to the database.
As part of the implementation, the application programmer will do the following: Create the CachedRowSet Bean and set its properties Register the Projector Bean as a listener to the rowset Create the GUI for the application and implement the actions of the open and close buttons Specify the rowset as a property on the form Bean To put this all together, the application programmer will probably use a visual Bean development tool, which means that he will use very little RowSet API directly.
Of course, the owner will use the application without writing any RowSet code himself. The upshot of all of this is that generally tools will generate the RowSet code you see in this tutorial. Also, remember that the code shown here is for illustrative purposes only because it uses the CachedRowSet class, for which there is no implementation currently available. Although the JDBC Standard Extension specification gives a preliminary outline of its functionality, some details in its implementation may be different when it is completed.
The main purpose of this section is to show you when and why you would want to set certain properties. The code for creating a CachedRowSet object simply uses the default constructor. These properties and a RowSet object's event notification capabilities explained in a later section are what make a RowSet object a JavaBeans component. A rowset's properties include its command, concurrency, type, data source name, url, user name, password, transaction isolation level, escape processing, maximum field size, maximum rows, query timeout, and type map.
You are required to set only those properties that are needed for your particular use of a rowset.
source url The following example uses several properties and explains why they are needed. The owner wants the convenience of being able to make updates by scrolling to the rows he wants to update, so the property for the type needs to be set to scrollable. It does no harm to set it, however. The default for the concurrency property is ResultSet. The following lines of code make the CachedRowSet object crset scrollable and updatable. The owner can then use the rowset to make his updates. However, he wants to use the preferred means of getting a connection, which is to use a DataSource object, so he will set the properties for the data source name, the owner's user name, and the owner's password.
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For security, the programmer may opt to get the user name and password from the owner interactively at run time, in which case he would not need to set them as properties. If you need a refresher on using a DataSource object to make a connection, start reading at page in the advanced tutorial.
Here is the code a tool would generate to set the command string, the data source name, the user name, and the password properties for the CachedRowSet object crset. When the rowset makes a connection, it will use the information in its properties, so the programmer or tool will not need to do anything except execute the command string, which you will see later.
Internally the rowset gives the JNDITM naming service the string the programmer set for the data source name property. The programmer sets one more property, the transaction isolation level, which determines the transaction isolation level given to the connection that the rowset establishes. The following line of code sets the rowset's property so that "dirty reads" will not be allowed.
If the owner has the programmer change the command string so that it gets data from a table that has user-defined types with custom mappings, then the type map property will need to be set. In the application we are considering, the Projector Bean needs to be notified when the rowset is updated, so it needs to be registered with the rowset as a listener. These methods specify what the listener will do when an event occurs on the CachedRowSet object crset.
The Projector Bean does not care about where the cursor is, so its implementation of cursorMoved is probably to do nothing. When one or more values in a row changes, the method rowChanged will be called on the listener.
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This method will probably check to see if the value in the PRICE or SALES columns has changed, and if either has changed, it will plug the appropriate value s into its projection model to get a value to display. The method rowSetChanged is invoked when the contents of the whole rowset change, which happens only when the rowset's command string has been changed and then executed. This method will probably have an implementation similar to that of the method rowChanged. The following line of code registers projector, the bar chart component, as a listener for crset.
The programmer will use his development tool to bring one more component into the application, the editor that will be used to update the rowset. He does this by simply specifying crset as a property on the editor. This tells the editor to which component it should send the changes keyed into it. Now all he has to do in order to get a scrollable and updatable rowset is to call the method execute on the rowset.
As a result of this call, the rowset does all of the following behind the scenes: The difference is that because the application developer has set the properties on the rowset to make it scrollable and updatable, the owner can move the cursor to any position in the rowset and modify its data. This is true even if the ResultSet object from which the rowset got its data is not scrollable or updatable.
In fact, it is especially when a JDBC driver does not support scrollable or updatable result sets that you might want to use a rowset as a means of getting those capabilities. The cursor is positioned before the first row in a newly-populated rowset, and a call to the method next moves the cursor to the first row. Thus, to iterate through a rowset from first row to last row, you call the method next in a while loop, just as you would do for a ResultSet object. With scrolling, you can move the cursor in any direction and can go to a row as many times as you like.
If you want a review of how to move the cursor, see the advanced tutorial section "Moving the Cursor in Scrollable Result Sets" on page The owner of The Coffee Break wanted a scrolling rowset so that he could easily make updates to a particular row.
The following section illustrates moving the cursor to update a row. The GUI tool displaying the rowset will generate the following line of code to move the cursor to the fifth row. The owner now moves the cursor to the price, which is the third column, and changes the column's value to In response, the GUI tool generates the following update statement.
This causes the GUI tool to generate the following line of code.