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It is possible to throw an exception a second time within a "catch" block. A script should hide system errors from users. System errors may be important for the coder, but is of no interest to the user.

Example explained: The code above tests if the email-address contains the string "example" in it, if it does, the exception is re-thrown: 1. The "try" block contains another "try" block to make it possible to rethrow the exception 5. The exception is triggered since the e-mail contains the string "example" 6. The "catch" block catches the exception and re-throws a "customException" 7. The "customException" is caught and displays an error message If the exception is not caught in its current "try" block, it will search for a catch block on "higher levels".

In the code above there was no "catch" block. Instead, the top level exception handler triggered. This function should be used to catch uncaught exceptions. Code may be surrounded in a try block, to help catch potential exceptions Each try block or "throw" must have at least one corresponding catch block Multiple catch blocks can be used to catch different classes of exceptions Exceptions can be thrown or re-thrown in a catch block within a try block.

What is a PHP Filter? A PHP filter is used to validate and filter data coming from insecure sources. To test, validate and filter user input or custom data is an important part of any web application. The PHP filter extension is designed to make data filtering easier and quicker.

Why use a Filter? Almost all web applications depend on external input. Usually this comes from a user or another application like a web service. By using filters you can be sure your application gets the correct input type. Page 65 of You should always filter all external data!

Input filtering is one of the most important application security issues. What is external data? Input data from a form Cookies Web services data Server variables Database query results. Since the integer is valid, the output of the code above will be: "Integer is valid". If we try with a variable that is not an integer like "abc" , the output will be: "Integer is not valid". Page 66 of Options and Flags Options and flags are used to add additional filtering options to the specified filters.

Different filters have different options and flags. Like the code above, options must be put in an associative array with the name "options". If a flag is used it does not need to be in an array. Since the integer is "" it is not in the specified range, and the output of the code above will be: "Integer is not valid". Check each filter to see what options and flags are available.

Validate Input Let's try validating input from a form. The first thing we need to do is to confirm that the input data we are looking for exists. Check if an "email" input variable of the "GET" type exist 2. If the input variable exists, check if it is a valid e-mail address. Let's try cleaning up an URL sent from a form. First we confirm that the input data we are looking for exists. Check if the "url" input of the "POST" type exists 2.

Filter Multiple Inputs A form almost always consist of more than one input field. Example Explained The example above has three inputs name, age and email sent to it using the "GET" method: 1. Set an array containing the name of input variables and the filters used on the specified input variables 2. Page 70 of If the parameter is a single filter ID all values in the input array are filtered by the specified filter.

If the parameter is an array it must follow these rules: Must be an associative array containing an input variable as an array key like the "age" input variable The array value must be a filter ID or an array specifying the filter, flags and options. This way, we have full control of the data filtering.

You can create your own user defined function or use an existing PHP function The function you wish to use to filter is specified the same way as an option is specified. What is MySQL? MySQL is a database.

The data in MySQL is stored in database objects called tables. A table is a collections of related data entries and it consists of columns and rows.

Databases are useful when storing information categorically. A company may have a database with the following tables: "Employees", "Products", "Customers" and "Orders". Database Tables A database most often contains one or more tables. Each table is identified by a name e. Tables contain records rows with data.

With MySQL, we can query a database for specific information and have a recordset returned. The query above selects all the data in the "LastName" column from the "Persons" table, and will return a recordset like this: LastName Hansen Svendson Pettersen. Perhaps it is because of this reputation that many people believe that MySQL can only handle small to medium-sized systems.

The truth is that MySQL is the de-facto standard database for web sites that support huge volumes of both data and end users like Friendster, Yahoo, Google.

Page 73 of Parameter Description servername Optional. Specifies the server to connect to. Default value is "localhost" username Optional.

Specifies the username to log in with. Default value is the name of the user that owns the server process Optional. Specifies the password to log in with.

Default is "". Note: There are more available parameters, but the ones listed above are the most important. Closing a Connection The connection will be closed automatically when the script ends. This function is used to send a query or command to a MySQL connection.

Page 75 of The following example creates a table named "Persons", with three columns. Important: A database must be selected before a table can be created. Note: When you create a database field of type varchar, you must specify the maximum length of the field, e. The data type specifies what type of data the column can hold. A primary key is used to uniquely identify the rows in a table. Each primary key value must be unique within the table. Furthermore, the primary key.

The following example sets the personID field as the primary key field. In the previous chapter we created a table named "Persons", with three columns; "Firstname", "Lastname" and "Age". We will use the same table in this example. When a user clicks the submit button in the HTML form in the example above, the form data is sent to "insert.

The "insert. Here is the "insert. The while loop loops through all the records in the recordset. The output of the code above will be: Page 81 of If you want to sort the records in a descending order, you can use the DESC keyword. Order by Two Columns It is also possible to order by more than one column.

Earlier in the tutorial we created a table named "Persons". Open the Administrative Tools icon in your Control Panel. Choose the System DSN tab. Select the Microsoft Access Driver. Click Finish. In the next screen, click Select to locate the database. Click OK. Note that this configuration has to be done on the computer where your web site is located.

If you are running Internet Information Server IIS on your own computer, the instructions above will work, but if your web site is located on a remote server, you have to have physical access to that server, or ask your web host to to set up a DSN for you to use. The function takes four parameters: the data source name, username, password, and an optional cursor type. The following example creates a connection to a DSN called northwind, with no username and no password.

This function returns true if it is able to return rows, otherwise false. This function takes two parameters: the ODBC result identifier and a field number or name. What is XML? XML is used to describe data and to focus on what data is. An XML file describes the structure of the data. In XML, no tags are predefined. You must define your own tags. What is Expat? There are two basic types of XML parsers:. Tree-based parser: This parser transforms an XML document into a tree structure.

It analyzes the whole document, and provides access to the tree elements. When a specific event occurs, it calls a function to handle it Page 91 of The Expat parser is an event-based parser.

Event-based parsers focus on the content of the XML documents, not their structure. Because of this, event-based parsers can access data faster than tree-based parsers. However, this makes no difference when using the Expat parser. Expat is a non-validating parser, and ignores any DTDs. Note: XML documents must be well-formed or Expat will generate an error.

There is no installation needed to use these functions. How it works: 1. Create functions to use with the different event handlers 3. Parse the file "test. What is DOM? It analyzes the whole document, and provides access to the tree elements Event-based parser: Views an XML document as a series of events. When a specific event occurs, it calls a function to handle it. The DOM parser is an tree-based parser. The output of the code above will be: Tove Jani Reminder Don't forget me this weekend!

In the example above you see that there are empty text nodes between each element. When XML generates, it often contains white-spaces between the nodes. The XML DOM parser treats these as ordinary elements, and if you are not aware of them, they sometimes cause problems. Page 97 of What is SimpleXML? It is an easy way of getting an element's attributes and text, if you know the XML document's layout.

When there's more than one element on one level, they're placed inside an array Attributes - Are accessed using associative arrays, where an index corresponds to the attribute name Element Data - Text data from elements are converted to strings. If an element has more than one text node, they will be arranged in the order they are found SimpleXML is fast and easy to use when performing basic tasks like: Reading XML files Extracting data from XML strings Editing text nodes or attributes. Installation As of PHP 5.

We want to output the element names and data from the XML file above. Here's what to do: 1. Load the XML file 2. Get the name of the first element 3. Create a loop that will trigger on each child node, using the children function 4. AJAX is not a new programming language, but simply a new technique for creating better, faster, and more interactive web applications. The AJAX technique makes web pages more responsive by exchanging data with the web server behind the scenes, instead of reloading an entire web page each time a user makes a change.

AJAX applications are browser and platform independent. Cross-Platform, Cross-Browser technology. Web applications have many benefits over desktop applications: they can reach a larger audience they are easier to install and support they are easier to develop However, Internet applications are not always as "rich" and user-friendly as traditional desktop applications. AJAX is based on open standards. These standards have been used by most developers for several years.

After the web server has processed the data, it will return a completely new web page to the user. Because the server returns a new web page each time the user submits input, traditional web applications often run slowly and tend to be less user friendly. With AJAX, web applications can send and retrieve data without reloading the whole web page.

This is done by sending HTTP requests to the server behind the scenes , and by modifying only parts of the web page using JavaScript when the server returns data.

XML is commonly used as the format for receiving server data, although any format, including plain text, can be used. You will learn more about how this is done in the next chapters of this tutorial. There is no such thing as an AJAX server. AJAX is a technology that runs in your browser. It uses asynchronous data transfer HTTP requests between the browser and the web server, allowing web pages to request small bits of information from the server instead of whole pages.

AJAX is a web browser technology independent of web server software. It has been available ever since Internet Explorer 5. Internet Explorer uses an ActiveXObject. Example above explained: 1. Set the value to null. Then test if the object window.

XMLHttpRequest is available. This object is available in newer versions of Firefox, Mozilla, Opera, and Safari. If it's not available, test if an object window. ActiveXObject is available. This object is available in Internet Explorer version 5. A Better Example? The example below tries to load Microsoft's latest version "Msxml2. If this catches an error, try the older Internet Explorer 5.

The form works like this: 1. An event is triggered when the user presses, and releases a key in the input field 2. When the event is triggered, a function called showHint is executed. This is used as a placeholder for the return data of the showHint function. This function executes every time a character is entered in the input field. If there is some input in the text field str.

Defines the url filename to send to the server 2. Adds a parameter q to the url with the content of the input field 3. Adds a random number to prevent the server from using a cached file 4. Sends an HTTP request to the server If the input field is empty, the function simply clears the content of the txtHint placeholder. When the state changes to 4 or to "complete" , the content of the txtHint placeholder is filled with the response text. The code above called a function called GetXmlHttpObject.

This is explained in the previous chapter. Page of The code in the "gethint. Find a name matching the characters sent from the JavaScript 2. If more than one name is found, include all names in the response string 3.

If no matching names were found, set response to "no suggestion" 4. If one or more matching names were found, set response to these names 5. The response is sent to the "txtHint" placeholder. The paragraph below the form contains a div called "txtHint". The div is used as a placeholder for info retrieved from the web server. When the user selects data, a function called "showCD" is executed. The execution of the function is triggered by the "onchange" event. In other words: Each time the user changes the value in the drop down box, the function showCD is called.

This document contains a CD collection. Example Explained The stateChanged and GetXmlHttpObject functions are the same as in the last chapter, you can go to the previous page for an explanation of those The showCD Function If an item in the drop down box is selected the function executes the following: 1. Defines the url filename to send to the server 3. Adds a parameter q to the url with the content of the input field 4.

Adds a random number to prevent the server from using a cached file 5. Call stateChanged when a change is triggered 6. Sends an HTTP request to the server. The CD containing the correct artist is found 4. The album information is output and sent to the "txtHint" placeholder.

When the user selects data, a function called "showUser " is executed. In other words: Each time the user changes the value in the drop down box, the function showUser is called. The showUser Function If an item in the drop down box is selected the function executes the following: 1. Adds a parameter q to the url with the content of the dropdown box 4. The "user" with the specified name is found 3. A table is created and the data is inserted and sent to the "txtHint" placeholder.

Receiving the response as an XML document allows us to update this page several places, instead of just receiving a PHP output and displaying it.

The HTML form is a drop down box called "users" with names and the "id" from the database as option values. The stateChanged Function If an item in the drop down box is selected the function executes the following: 1. Defines the "xmlDoc" variable as an xml document using the responseXML function 2. The PHP document is set to "no-cache" to prevent caching 3. The "user" with the specified id is found 6. The data is outputted as an xml document. Live search has many benefits compared to traditional searching: Matching results are shown as you type Results narrow as you continue typing If results become too narrow, remove characters to see a broader result.

In this example the results are found in an XML document links. To make this example small and simple, only eight results are available. When the event is triggered, a function called showResult is executed. This is used as a placeholder for the return data of the showResult function. The JavaScript code is stored in "livesearch. The showResult Function This function executes every time a character is entered in the input field. If there is no input in the text field str.

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