265 lines
13 KiB
HTML
265 lines
13 KiB
HTML
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<title>Strolch: Overview</title>
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<a class="navbar-brand" href="index.html">Strolch</a>
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<li class="active"><a href="index.html">Overview</a></li>
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<li><a href="api.html">API</a></li>
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<li><a href="documentation.html">Documentation</a></li>
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<div class="container">
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<div class="page-header">
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<h1 class="page-title">Strolch Overview</h1>
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<p class="lead page-description">This page describes the Strolch software agent and the motivation behind its
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development.</p>
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</div>
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<div class="content">
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<h2>Overview</h2>
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<p>Strolch is an open source component based software agent written in Java and can be compared, in a light
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sense, with the Java EE stack: Strolch takes care of persistence, implements Services for use cases, Commands
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as re-usable algorithms and has a parameterized data model.</p>
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<p>Strolch has an intrinsic understanding for mandates, which are called realms so that a single agent can be
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used to implement applications with multiple users/customers for instance in SaaS environments.</p>
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<p>The parameterized data model consists of three top level objects, Resources, Orders and Activities. These
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objects can have any number of ParameterBags which in turn can have any number of Parameters on them. This
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allows for a very dynamic modelling of data structures including modification at run time. Multiple ready to
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use Parameter types are already implemented which handle the primitive types in Java including ListParameters
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for collections of these primitive types.</p>
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<p>One of the main features of the Strolch agent, is that persistence is handled transparently and the user must
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not be worried about databases and the likes. Currently there are two implementations for persisting the
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Strolch model, a PostgreSQL and an XML file persistence. Currently both persistence layers persist the data
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by converting to XML and storing it into the database. The XML file persistence stores each object in its own
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file.</p>
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<p>The agent itself has a small memory footprint and requires very few components to start. For the agent to be
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useful it needs additional functionality which is implemented in StrolchComponents. Each component is
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registered via its Java interface on the agent and is bound to the life cycle of the agent. When the agent is
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started, these components can be retrieved and used to perform any number of functionalities. This is the
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preferred way to extend the Strolch agent. There are a number of components already implemented, e.g. the
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ServiceHandler which executes Services in a controlled fashion and can validate authorized access to these
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services.</p>
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<p>No software product is complete without a system for authentication and authorization. Strolch implements
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this by using the Privilege framework which has been written by Robert von Burg. The standard ServiceHandler
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detects the existence of the PrivilegeHandler and then validates that the user has authorization to perform
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the service. This framework is implemented as its own Strolch component, thus can be retrieved at any time
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during execution to perform fine grained and special authorization validation.</p>
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<h2>Motivation</h2>
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<p>A question often asked is why create Strolch. What are its benefits in contrast to using Java SE with an
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OR-Mapper like Hibernate, or using Java EE on JBoss or Glassfish? Especially since many of the features
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existing in those stacks needed to be re-created in Strolch.</p>
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<p>The first answer to this question is that those systems are often overly complicated and bloated. Java SE
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with Hibernate certainly is a viable option when it comes to being light-weightier but Hibernate, even though
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it is supposed to, often fails to truly help remove the need to really understand an RDBMS. Often enough
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Hibernate will just get in the way of the most important part of development: writing the business code.
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Being an OR-Mapper which is supposed to implement all the nitty-gritty details of an RDBMS system, Hibernate,
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and JPA for that matter, still often has the developer go back to understanding these details.</p>
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<p>Strolch tries a different approach to persistence. Instead of writing pojos/entities, Strolch's model has the
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concept that each element's attributes are part of a composition pattern: each attribute is its own object
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and thus can be dynamically changed at runtime, but also makes persistence of such an element generic.
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Instead of having fixed attributes for a concrete class, these parameters are stored in a map and are
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accessed through the parameter's ID.</p>
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<p>Assigning an ID to an attribute for accessing of course brings its own downsides, i.e. the parameter might
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simply not be there, when being accessed. This is certainly an issue that the developer must handle, when
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implementing a project using Strolch, but allows the developer to not need to worry about persistence, as
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this is generically handled.</p>
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<p>Since the persistence is generically handled, and Strolch stays lightweight on its requirements at runtime,
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the developer can quickly get down to what is important for business value: Writing the business logic and
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the presentation layer. Here too Strolch tries to help the developer by bringing in concepts which are easy
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to follow: Use cases are implemented as Services, and re-usable business logic is put into Commands.</p>
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<p>There will be reasons against using Strolch, as there will be against using the Java EE stack, or an
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OR-Mapper or even the Java ecosystem for that fact. Important is to note, that the concepts behind Strolch
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are nothing new, but have been implemented in at least two previous proprietary products. Since those
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products are not accessible to the public, it was decided that a re-implementation might be of use to the
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programming community at large.</p>
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<p>Currently there is at least one company using Strolch in a commercial project which helps drive Strolch's
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development and further motivates its existence.</p>
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<p>Strolch is an open source project and licensed under the Apache License 2.0.</p>
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<h2>Technologoy</h2>
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<p>Strolch is written in Java and is programmed against the JDK 8. Strolch runs on any JRE 8 compliant
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environment. Strolch is tested on the Oracle JRE 8.</p>
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<h3>Dependencies</h3>
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<p>Strolch strives to use as few external dependencies as possible, so that the Strolch runtime is not bloated
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unnecessarily. The following list of Strolch dependencies is a summary and was created using mvn
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dependency:tree on the strolch_minimal project for release 1.6.47.</p>
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<p>Logging</p>
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<ul>
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<li>org.slf4j:slf4j-api:jar:1.7.25</li>
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<li>ch.qos.logback:logback-classic:jar:1.2.3</li>
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<li>ch.qos.logback:logback-core:jar:1.2.3</li>
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</ul>
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<p>Utils</p>
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<ul>
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<li>javax.mail:javax.mail-api:jar:1.6.0</li>
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<li>com.sun.mail:javax.mail:jar:1.6.0</li>
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<li>javax.activation:activation:jar:1.1</li>
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</ul>
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<p>Testing</p>
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<ul>
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<li>junit:junit:jar:4.12</li>
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<li>org.hamcrest:hamcrest-core:jar:1.3</li>
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<li>org.hamcrest:hamcrest-library:jar:1.3</li>
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<li>org.mockito:mockito-core:jar:2.0.8-beta</li>
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<li>org.objenesis:objenesis:jar:2.1</li>
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</ul>
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<p>Model</p>
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<ul>
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<li>com.google.code.gson:gson:jar:2.8.2</li>
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</ul>
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<p>SOQL</p>
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<ul>
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<li>org.abego.treelayout:org.abego.treelayout.core:jar:1.0.3</li>
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<li>org.antlr:antlr-runtime:jar:3.5.2</li>
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<li>org.antlr:antlr4-runtime:jar:4.7</li>
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<li>org.antlr:antlr4:jar:4.7</li>
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<li>org.antlr:ST4:jar:4.0.8</li>
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<li>org.glassfish:javax.json:jar:1.0.4</li>
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<li>com.ibm.icu:icu4j:jar:58.2</li>
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</ul>
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<p>PostgreSQL</p>
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<ul>
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<li>com.zaxxer:HikariCP:jar:2.7.1</li>
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<li>org.postgresql:postgresql:jar:42.1.4</li>
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</ul>
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<p>REST</p>
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<ul>
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<li>javax.annotation:javax.annotation-api:jar:1.3.1</li>
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<li>javax.servlet:javax.servlet-api:jar:3.1.0</li>
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<li>javax.ws.rs:javax.ws.rs-api:jar:2.1</li>
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</ul>
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<p>REST testing</p>
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<ul>
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<li>javax.validation:validation-api:jar:1.1.0.Final</li>
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<li>org.glassfish.grizzly:grizzly-framework:jar:2.3.28</li>
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<li>org.glassfish.grizzly:grizzly-http-server:jar:2.3.28</li>
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<li>org.glassfish.grizzly:grizzly-http-servlet:jar:2.3.28</li>
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<li>org.glassfish.grizzly:grizzly-http:jar:2.3.28</li>
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<li>org.glassfish.hk2:hk2-api:jar:2.5.0-b32</li>
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<li>org.glassfish.hk2:hk2-locator:jar:2.5.0-b32</li>
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<li>org.glassfish.hk2:hk2-utils:jar:2.5.0-b32</li>
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<li>org.glassfish.hk2:osgi-resource-locator:jar:1.0.1</li>
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<li>org.glassfish.hk2.external:aopalliance-repackaged:jar:2.5.0-b32</li>
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<li>org.glassfish.hk2.external:javax.inject:jar:2.5.0-b32</li>
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<li>org.glassfish.jersey.bundles.repackaged:jersey-guava:jar:2.25.1</li>
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<li>org.glassfish.jersey.containers:jersey-container-grizzly2-http:jar:2.25.1</li>
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<li>org.glassfish.jersey.containers:jersey-container-grizzly2-servlet:jar:2.25.1</li>
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<li>org.glassfish.jersey.containers:jersey-container-servlet-core:jar:2.25.1</li>
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<li>org.glassfish.jersey.containers:jersey-container-servlet:jar:2.25.1</li>
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<li>org.glassfish.jersey.core:jersey-client:jar:2.25.1</li>
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<li>org.glassfish.jersey.core:jersey-common:jar:2.25.1</li>
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<li>org.glassfish.jersey.core:jersey-server:jar:2.25.1</li>
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<li>org.glassfish.jersey.media:jersey-media-jaxb:jar:2.25.1</li>
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<li>org.glassfish.jersey.test-framework:jersey-test-framework-core:jar:2.25.1</li>
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<li>org.javassist:javassist:jar:3.20.0-GA</li>
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</ul>
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<h4>API</h4>
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<p>Check out the <a href="api.html">API page</a> to see how to use Strolch.</p>
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<p class="text-muted">© Strolch / <a href="mailto:eitch@eitchnet.ch">Robert von Burg</a> / Hosting by
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<a href="http://www.eitchnet.ch">eitchnet.ch</a></p>
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