Home > Articles > Programming > Java

  • Print
  • + Share This
Like this article? We recommend

A Simple AOP Example

Suppose we have a simple class that takes a number from user input and determines whether that number is prime. Several ways are available to perform such a check, and Joe, the author of this class, is overly cautious: He has written three separate methods for verification, and the number entered is said to be prime only if all three methods agree. Here's the application code:

public class ComplexFormulae
{
  /**
   * Highly inefficient but overly thorough algorithm
   */
  public boolean isPrimeOne(BigInteger number)
  {
    BigInteger testNumber = new BigInteger("2");

    while(testNumber.compareTo(number) < 0)
    {
      if(number.mod(testNumber).equals(
        new BigInteger("0")))
      {  return false;  }
      testNumber = testNumber.add(
        new BigInteger("1"));
    }

    return true;
  }

  /**
   * Slightly more efficient algorithm
   */
  public boolean isPrimeTwo(BigInteger number)
  {
    BigInteger testNumber = new BigInteger("2");

    while(testNumber.compareTo(
      number.divide(new BigInteger("2"))) <= 0)
    {
      if(number.mod(testNumber).equals(
        new BigInteger("0")))
      {  return false;  }

      testNumber = testNumber.add(
        new BigInteger("1"));
    }

    return true;
  }

  /**
   * Reliant on the BigInteger class, unknown performance
   */
  public boolean isPrimeThree(BigInteger number)
  {
    return number.isProbablePrime(50);
  }

  public static void main(String[] args)
  {
    ComplexFormulae   formulae  = new ComplexFormulae();
    BufferedReader   reader   = null;
    BigInteger     number   = null;
    String       numberStr  = "";

    boolean       isPrimeOne   = false;
    boolean       isPrimeTwo   = false;
    boolean       isPrimeThree  = false;

    reader = new BufferedReader(
      new InputStreamReader(System.in));

    while(number == null)
    {
      System.out.println(
        "Please enter the number to test:");
      try
      {  numberStr = reader.readLine(); }
        catch(Exception e)
        {
          System.out.println(
            "Error reading input: " + e);
          System.exit(1);
        }
      try
      {  number = new BigInteger(numberStr.trim()); }
        catch(NumberFormatException nfe)
        {
          System.out.println(numberStr +
            " is not a number!" + '\n' + nfe);
        }
    }

    isPrimeThree = formulae.isPrimeThree(number);
    isPrimeTwo = formulae.isPrimeTwo(number);
    isPrimeOne = formulae.isPrimeOne(number);

    if(isPrimeThree && isPrimeTwo && isPrimeOne)
      System.out.println(numberStr +
        " is a prime number!");
    else
      System.out.println(numberStr +
        " is not a prime number!");

  }
}

Now Speed It Up, Jack

Unfortunately, running the sample code I just showed you on any prime number greater than 219–1 (the next greatest is 2,147,483,647) takes a very long time to complete on most computers. What's taking so long? The typical brute-force way to find out would be to change the code and put in some timing logic. Or you could run the code through a debugger or performance analyzer and get timings that way. But AOP provides a rather easy way to do just that without changing code, recompiling, or relying on any debugging or profiling tools.

The first thing we need to do is code an instance of Interceptor—the class that JBoss uses to intercept method calls, field access, object instantiation, etc. It's a simple interface, requiring only two methods of the implementer. In this case, we want to intercept any calls to the three methods above, track how long they take to execute, and print the method name and the timing after the methods have completed. The code to do so is quite simple:

public class PerformanceInterceptor implements Interceptor
{
  public String getName()
  {  return "PerformanceInterceptor";  }

  public Object invoke(Invocation invocation) throws Throwable
  {
    long  startTime  = new Date().getTime();
    long  endTime   = 0l;
    MethodInvocation   methodInvoke  = null;

    //Must ensure that this is only bound to method
    // invocations, else ClassCastException will ensue
    methodInvoke = (MethodInvocation)invocation;

    try
    {  return invocation.invokeNext(); }
    finally
    {
      endTime = new Date().getTime();
      System.out.println("Execution of " +
        methodInvoke.actualMethod.getName() +
        " took " + (endTime - startTime) + " millis");
    }
  }
}

The work is handled in the invoke() method. This method receives an instance of Invocation, a JBoss class, which contains all the information required to determine what is being intercepted. In this case, we'll be receiving a MethodInvocation instance, as a method is being intercepted, and we use it only to get the name of the method being intercepted. But, with similar code, it would be easy to modify the parameters we pass along to the method being intercepted, change the return values from that method, modify exception handling, or simply absorb the method call and do nothing.

The trick is to bind this PerformanceInterceptor class back to our underperforming ComplexFormulae class, and that's achieved through a combination of an XML configuration file and a custom classloader. First, the configuration file:

<?xml version="1.0" encoding="UTF-8"?>
<aop>
  <bind pointcut=
    "execution(public boolean ComplexFormulae->isPrime*(*))">
    <interceptor class="PerformanceInterceptor"/>
  </bind>
</aop>

The <bind> element indicates which methods to intercept, and what to do with them. The pointcut attribute specifies a statement much like a regular expression, identifying the points to intercept. In this case, we're looking for public methods within the ComplexFormulae class that return a type Boolean and have a name that begins with isPrime. If we also wanted to time the main() method, we could make a simple change to indicate all public methods:

<?xml version="1.0" encoding="UTF-8"?>
<aop>
  <bind pointcut=
    "execution(public * ComplexFormulae->*(*))">
    <interceptor class="PerformanceInterceptor"/>
  </bind>
</aop>

Now, any public method, regardless of name or return type, will be timed. Of course, we're assuming that you run your code through the JBoss AOP classloader. To do that, save the above XML code into a file (generally jboss-aop.xml, but we'll use performance-binding.xml here), and provide the following two system parameters on your call to Java:

java -Djava.system.class.loader=org.jboss.aop.standalone.SystemClassLoader
-Djboss.aop.path=performance-binding.xml ComplexFormulae

Running the above command using the second binding file will render output that looks something like this:

Please enter the number to test:
2147483647
Execution of ComplexFormulae$isPrimeThree$WithoutAdvisement took 16 millis
Execution of ComplexFormulae$isPrimeTwo$WithoutAdvisement took 2778875 millis
Execution of ComplexFormulae$isPrimeOne$WithoutAdvisement took 3162281 millis
2147483647 is a prime number!
Execution of ComplexFormulae$main$WithoutAdvisement took 5943734 millis

Altering the Example by Circumvention

isPrimeThree(), the method that relies on the BigInteger.isProbablePrime() method, vastly outpaces the other, more "thorough" methods. Faced with these facts, and facing customers screaming about the performance of this application, we can disable the two slower methods. But suppose that the coder who's responsible for this class is on vacation and the code isn't accessible to anyone else! No problem, as circumventing those methods' execution via AOP is a piece of cake. Simply change the invoke() method on our Interceptor class to look like this:

public Object invoke(Invocation invocation) throws Throwable
{
  try
  {  return new Boolean(true);  }
  finally
  {}
}

And change our XML binding to intercept only the two methods we want to switch off:

<bind pointcut=
  "execution(public * ComplexFormulae->isPrimeOne(*))">
  <interceptor class="PerformanceRedirector"/>
</bind>
<bind pointcut=
  "execution(public * ComplexFormulae->isPrimeTwo(*))">
  <interceptor class="PerformanceRedirector"/>
</bind>

Now, whenever isPrimeOne() or isPrimeTwo() is called, a Boolean value of true will always be returned nearly instantly, meaning that the application relies entirely on isPrimeThree().

CAUTION

This is a great fix, right?

Perhaps to some. But to many coders (including me), the ease of doing something like this is a little disconcerting. We've now radically changed the behavior of the application, yet nothing in the code has been modified to indicate this change, and unless the change is well-documented somewhere, when Joe comes back from vacation he's liable to be rather confused. While this is an unrealistic example, it's easy to see how AOP can be a dangerous weapon without clear policies and best practices. This is why care must be exercised when adopting AOP development, as its benefits in making quick and sweeping modifications to application behavior are often outweighed by the need for new process controls and documentation.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020