SystemPropertiesPicoContainer

SystemPropertiesPicoContainer is a special type of PicoContainer that is populated from the System Properties passed into the Java application when it started.

Here is an example of how to use SystemPropertiesPicoContainer to map system properties as configuration for a component, with parameter names as the bindings.

Consider this component:

public class BigFatComponent { 
  URL spellWebService; 
  int timeout;
  public BigFatComponent(String spellingWebServiceURL, int timeout) throws MalformedURLExeption {
    this.spellWebService = new URL(spellingWebServiceURL); 
    this.timeout = timeout;
  }
  public String toString() { 
    return "URL=" + spellWebService + ", timeout=" + timeout; 
  } 
  // other methods 
}

For automatic binding of system properties to parameter names of the component:

PicoContainer syspropsContainer = new SystemPropertiesPicoContainer(); 
MutablePicoContainer mpc = new DefaultPicoContainer(syspropsContainer); 
mpc.as(Characteristics.USE_NAMES).addComponent(BigFatComponent.class);

Here is another manual use forcing an association between a system properties, and the relative position of a parameter in the constructor. It is most useful when there is not a tie-up between the parameter names and the system properties. In this case the arg passed in to the ConfigParameter (varargs list) is the one that matches the system property name:

mpc.addComponent(BigFatComponent.class, ConfigParameter("wsURL"), ConfigParameter("serviceTimeout"));

System properties can be set for the scope of the application only, as you start the application:

java -Dwebservice.url=http://servicehost/service -Dwebservice.timeout=50 -jar myAppJar.jar -cp picocontainer-2.0.jar

Type conversion is automatic in many cases. Properties in a properties file are clearly strings. Parameters can be any of:

• String
• All numeric types, boxed as well as primitives
• java.util.Date
• java.io.File as well as java.io.URL
• java.util.Date

• java.sql.(Date

  Time

  Timestamp)

• Any type sporting accessible constructor taking single string parameter.

SystemPropertiesPicoContainer can be part of a tree of containers. It makes sense, of course, being more near the root of that tree.