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Professional Open Source

Implementing Middleware with AOPJBoss Aspect Oriented Middleware

Topics

Overview From Interceptors to Aspects

– J2EE a la carte– AOP + metadata

From Aspects to EJB3– Proxy based AOP– AOP Domains– Annotations as Meta Model– XML + Annotations

Dynamic AOP– Transparent caching– JBoss Cache Demo– Designing a Cache

AOP and Middleware

Middleware is but a collection of cross-cutting concerns Most middleware already sort of aspectized

– CORBA and JBoss heavy use of interceptors

Basing designs on AOP natural step Expensive to use regular OOP techniques to mix/match

configurations Application is just configuration a set of cross-cutting concerns

– Natural step is to implement middleware using AOP– More modular designs– Less code clutter

AOP and Middleware

Aspect Oriented Middleware brings transparency System aspects can be made orthonogal Application code can free of system programming Middleware can be made simpler to use

AOP Makes things Easier

AOP to implement Ease-of-Use– EJB 3 and annotation library implemented with AOP

AOP for Ease-of-Extension– Ease-of-use frameworks written on top of AOP– AOP gives easy consistent way to extend behavior

From Interceptors To AspectsJBoss 3.x to JBoss AOP

JBoss 3.x Architecture

– J2EE behavior expressed as interceptors

– Detyped method invocations

Client JVMJM

X Microkernel

icrokernel

Server JVM

EJB Container MBean

011101010101

RemoteInvokerRemoteInvoker

Typed Interface

Client Proxy

EJB Container MBean

Service MBean

Invocation

Port 1234

Port 4321ClientClient

– Internally invocation objects are routed within the kernel

Cross-cutting Concern

<container-configuration>

<container-name>Standard CMP 2.x EntityBean</container-name>

<container-interceptors>

<interceptor>org.jboss.ejb.plugins.ProxyFactoryFinderInterceptor</interceptor>

<interceptor>org.jboss.ejb.plugins.LogInterceptor</interceptor>

<interceptor>org.jboss.ejb.plugins.SecurityInterceptor</interceptor>

<interceptor>org.jboss.ejb.plugins.TxInterceptorCMT</interceptor>

<interceptor>org.jboss.ejb.plugins.CallValidationInterceptor</interceptor>

<interceptor>org.jboss.ejb.plugins.EntityCreationInterceptor</interceptor>

<interceptor>org.jboss.ejb.plugins.EntityLockInterceptor</interceptor>

<interceptor>org.jboss.ejb.plugins.EntityInstanceInterceptor</interceptor>

<interceptor>org.jboss.ejb.plugins.EntityReentranceInterceptor</interceptor>

<interceptor>org.jboss.resource.connectionmanager.CachedConnectionInterceptor</interceptor>

<interceptor>org.jboss.ejb.plugins.EntitySynchronizationInterceptor</interceptor>

<interceptor>org.jboss.ejb.plugins.cmp.jdbc.JDBCRelationInterceptor</interceptor>

</container-interceptors>

Cross-cutting Concern

Extract Aspects

Interceptors to Aspects

Aspectizing JBoss seemed like logical next step Leverage pointcut expressions Bring J2EE a la cart to plain Java Leverage our existing interceptor design

J2EE a la carte

Transaction Demarcation

Transaction demarcation (method, field, constructor) You can specify transaction boundaries within code Tags can transparently interact with Transaction Manager

– Begin, suspend, commit and rollback transactions

– On method, field, or constructor execution

EJB adjectives used to specify transactional behavior– Required, RequiresNew, Supports, Never, NotSupported, Mandatory

Complete control over when a rollback is triggered– i.e. which thrown exceptions cause a rollback

Transaction Demarcation

Annotations or XML metadata can specify annotation

@Tx(TxType.REQUIRED)

public void somepojoMethod() { … }

@Tx(TxType.REQUIRED)

public void somepojoMethod() { … }

<value>RequiresNew</value>

</method></metadata>

<value>RequiresNew</value>

</method></metadata>

Roled-based Security

Secured access to any method, field, or constructor Only users of a certain role allowed to access Authentication/Authorization integrated with JBoss Security

– Various Security Domains (LDAP, RDBMS, SRP, etc…)

Access to username available within other interceptors

Role-Based security

JDK 5.0 Annotations are usable

@SecurityDomain(“other”)

public class POJO {

@Unchecked public POJO() {}

@Exclude public exlucedMethod() {…}

@Permissions({“admin”, “manager”})

public void someMethod() {…}

@Permissions({“user”})

public static int status;

@SecurityDomain(“other”)

public class POJO {

@Unchecked public POJO() {}

@Exclude public exlucedMethod() {…}

@Permissions({“admin”, “manager”})

public void someMethod() {…}

@Permissions({“user”})

public static int status;

Role-Based security

XML metadata can specify annotation

<metadata tag="security" class="org.jboss.test.aop.bean.SecuredPOJO"> <security-domain>other</security-domain> <method-permission> <role-name>allowed</role-name> <method><method-name>someMethod</method-name></method> </method-permission> <constructor-permission> <unchecked/> <constructor><constructor-params/></constructor> </constructor-permission> <exclude-list> <description>Methods that connect be used</description> <method> <method-name>excluded</method-name> </method> </exclude-list></metadata>

Metadata

J2EE a la carte examples show importance of metadata Pointcut expressions aren’t always the silver bullet Can be confusing to developers

– Developers want simple, familiar ways of applying aspects

– Some developers like annotations

– Others prefer XML to externalize configuration

– An AOP framework needs to be aware of both.

Metadata

JBoss AOP requirements– Support annotations in pointcut expressions

– Support annotation overrides at runtime

– Support untyped metadata

– Support metadata/annotation defaults

– Support XML externalization of metadata

Allow metadata/annotations to be attached without modifying bytecode Metadata changeable on a per-deployment basis through XML Allow pointcut expressions to be aware of this attached metadata.

Dynamic Metadata

Aspects can resolve metadata dynamically The AOP Invocation object (ThisJoinPoint) gives hooks for this. Metadata can be attached to a invocation and propagated

– Aspects can pass information to one another locally or remotely

Metadata can be overridden on a per Thread basis– Change behavior per Thread

– Provide simple mechanism to clear all Thread metadata (Thread Pooling)

Default values can be defined/managed per VM or per Cluster

Invocation Thread Class VM Cluster

EJB 3.0 and JBoss AOPAn aspect-oriented EJB container

EJB 3.0 and JBoss AOP

Can EJB be implemented using AOP? “Traditional” AspectJ like weaving not possible

– EJB is a proxy architecture by definition

– proxy.someMethod() different behavior than this.someMethod()

– Same class can be deployed in multiple containers

– Mix/match of XML and Annotations

JBoss 3.x and lower showed AOP was the right approach A Proxy-based AOP container was needed.

JBoss AOP binds aspects at class load time Since binding is java.lang.reflection based Very easy to create a proxy container a.k.a an EJB container

Client JVMJB

oss Rem

otingJB

oss Rem

Server JVM

AOP Container

011101010101

Typed Interface

Client Proxy

AOP ContainerInvocation

Port 1234

Port 4321ClientClient

Why re-architect within an AOP Container?– Full pointcut expressions available

– Per method advice chains

– Pluggable annotations

– Pluggable behavior

– Reuse existing Aspect Library

Remember?– If middleware is easy to use…

– …it should also be easy to extend

– AOP allows us to easily extend EJB behavior

The next issue: EJB Containers have similar, but different aspects

– Stateless, Stateful, MDB (and JBoss extensions)

Proxies to these container types also similar but different Needed a way to define a template for each of these types Needed a way to define a template for proxy definition Solution:

– JBoss AOP “Aspect Domains”

Aspect Domains

Advice Stacks:– Named chain of unbound advices

– Proxies use these to understand what their advices should be

Aspect Domains:– Define a set of pointcuts, metadata overrides, and advice bindings

– Containers reference domains for their advices

– Domains can inherit from one-another

Advice stacks

<interceptor-ref name="org.jboss.aspects.remoting.IsLocalInterceptor"/>

<interceptor-ref name="org.jboss.aspects.security.SecurityClientInterceptor"/>

<interceptor-ref name="org.jboss.aspects.tx.ClientTxPropagationInterceptor"/>

<interceptor-ref name="org.jboss.aspects.remoting.InvokeRemoteInterceptor"/>

</stack>

<interceptor-ref name="org.jboss.aspects.remoting.IsLocalInterceptor"/>

<interceptor-ref name="org.jboss.aspects.security.SecurityClientInterceptor"/>

<interceptor-ref name="org.jboss.aspects.tx.ClientTxPropagationInterceptor"/>

<interceptor-ref name="org.jboss.aspects.remoting.InvokeRemoteInterceptor"/>

</stack>

Containers reference advice stacks when they create proxies Stacks are predefined and configurable

<interceptor-ref name="org.jboss.ejb3.security.AuthenticationInterceptorFactory"/>

<interceptor-ref name="org.jboss.ejb3.security.RoleBasedAuthorizationInterceptorFactory"/>

</bind>

<interceptor-ref name="org.jboss.ejb3.security.RunAsSecurityInterceptor"/>

</bind>

<interceptor-ref name="org.jboss.ejb3.stateless.StatelessInstanceInterceptor"/>

<interceptor-ref name="org.jboss.aspects.tx.TxPropagationInterceptor"/>

<interceptor-ref name="org.jboss.ejb3.tx.TxInterceptorFactory"/>

</bind>

@org.jboss.ejb3.PoolClass (value=org.jboss.ejb3.ThreadlocalPool.class, maxSize=30, timeout=10000)

</annotation>

</domain>

<interceptor-ref name="org.jboss.ejb3.security.AuthenticationInterceptorFactory"/>

<interceptor-ref name="org.jboss.ejb3.security.RoleBasedAuthorizationInterceptorFactory"/>

</bind>

<interceptor-ref name="org.jboss.ejb3.security.RunAsSecurityInterceptor"/>

</bind>

<interceptor-ref name="org.jboss.ejb3.stateless.StatelessInstanceInterceptor"/>

<interceptor-ref name="org.jboss.aspects.tx.TxPropagationInterceptor"/>

<interceptor-ref name="org.jboss.ejb3.tx.TxInterceptorFactory"/>

</bind>

@org.jboss.ejb3.PoolClass (value=org.jboss.ejb3.ThreadlocalPool.class, maxSize=30, timeout=10000)

</annotation>

</domain>

Aspect Domains

Annotation Override

Annotations with behavior

Default advices

Dynamic AOPTransparent caching

What is Dynamic AOP ?

Hot-deployment of aspects Bind/unbind advices arbitrarily at runtime Per-instance AOP Add advices on a per instance basis

What is JBossCache ?

Transparent caching Local or replicated

– Synchronous or asynchronous replication (using JGroups)

Transactional or non-transactional– Transactional

• Replication at TX commit

• DB isolation levels supported

• Support for pluggable TxManagers

– Non-Transactional

• Replication after each modification

Pluggable eviction policies– Ships with time-based and size-based (LRU) policies

Cache loader– Persistent backend store (load - store)

AOP Cache

Work with POJOs

public class Person { String name=null; int age=0; Map hobbies=null; Address address=null; Set skills; List languages;

public String getName() { return name; }

public void setName(String name) { this.name=name; } ...}

public class Person { String name=null; int age=0; Map hobbies=null; Address address=null; Set skills; List languages;

public String getName() { return name; }

public void setName(String name) { this.name=name; } ...}

public class Address { String street=null; String city=null; int zip=0;

public String getStreet() { return street; }

public void setStreet(String street) { this.street=street; } ...}

public class Address { String street=null; String city=null; int zip=0;

public String getStreet() { return street; }

public void setStreet(String street) { this.street=street; } ...}

Interaction With Cache

tree = new TreeCacheAop();

config = new PropertyConfigurator();// configure tree cache.config.configure(tree, "META-INF/replSync-service.xml");

joe = new Person();joe.setName("Joe Black");joe.setAge(31);

addr = new Address();addr.setCity("Sunnyvale");addr.setStreet("123 Albert Ave");addr.setZip(94086);

joe.setAddress(addr);

tree = new TreeCacheAop();

config = new PropertyConfigurator();// configure tree cache.config.configure(tree, "META-INF/replSync-service.xml");

joe = new Person();joe.setName("Joe Black");joe.setAge(31);

addr = new Address();addr.setCity("Sunnyvale");addr.setStreet("123 Albert Ave");addr.setZip(94086);

joe.setAddress(addr);

Use Pojos as Pojos

Interaction With Cache

Joe’s state is automatically transactional and replicated State replicated, synchronized at transaction commit/rollback

tree.start(); // kick start tree cachetree.putObject("/aop/joe", joe); // add aop sanctioned object

tx.begin();joe.setAge(41);joe.getAddress().setZip(95124);tx.commit();

tree.start(); // kick start tree cachetree.putObject("/aop/joe", joe); // add aop sanctioned object

tx.begin();joe.setAge(41);joe.getAddress().setZip(95124);tx.commit();

Demo JBossCache

How does it work?

<?xml version="1.0" encoding="UTF-8"?>

</aop>

<?xml version="1.0" encoding="UTF-8"?>

</aop>

Classes must be prepared for field interception This preparation creates AOP hooks Any advice can be added where hooks are instrumented

How does it work?

Uses reflection to discover the structure of a POJO– Requires a jboss-aop.xml to declare user-defined class to be “advisable“

– Uses AOP to keep track of changes to a POJO

putObject() breaks an object apart and maps it to the TreeCache– Primitive fields are mapped to entries in a node's attributes

– Complex fields are mapped to child nodes (recursively)

• Transparent handling of object hierarchies

• No need for one-to-one, one-to-many, etc relationship declarations

• POJO inheritance hierarchy is preserved

– We dynamically add a field advice to each complex object to keep track of state changes

JBoss Cache - Advices

Each advice remembers the node to which it maps– On field read: advice returns the value from the TreeCache

– On field write: advice updates the associated node's attributes, e.g.

– person.getAddress().setCity("San Jose“) generates a put("/322649/addr", "city", "San Jose")

On TX commit: modified fields are replicated and written back to the POJO

JBoss Cache - Design

Cache design itself can aspectized Cache Aspects

– CacheLoader, cache persistence

– Replication

– Transactionality

Cannot aspectize using class-level weaving Same classes but configured differently per instance Aspects can only be assembled if AOP framework support Dynamic AOP

JBoss Strategy

Middleware is the perfect application of AOP– Transparency

– Flexibility

Annotations for ease of use AOP for ease of extension

Professional Open Source © JBoss, Inc. 2003-2005. 1 2/6/2014 Professional Open Source © JBoss...

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