本文是<<struts2 技术内幕>>的学习笔记

在进行面向对象编程的时候,我们不可避免地要使用继承实现等等java提供的语法支持。但是复杂的对象关系也为对象生命周期的管理带来了至少以下两个问题。

对象的生命管理周期

public class Person{
    private Car car;

    public Person(Car c){
    this.car=c;
    }
    public void drive(){
    car.drive();
    }
}

public class Person{
    private Car car;

    public Person(){
    //其他代码
    }
    public void setCar(Car c){
    this.car=c;
    }
    public void drive(){
    car.drive();
    }
}

XWork容器的定义

public interface Container extends Serializable {

  /**
   * Default dependency name.
   */
  String DEFAULT_NAME = "default";

  /**
   * 创建类的实例,并进行注入 在上面说的person与car的例子中
   * injcet的参数就应该是person
   * object内部声明有@inject的字段和方法都将被注
   * 入容器所托管的对象(例如上面说的car)
   */
  void inject(Object o);

 
  <T> T inject(Class<T> implementation);

  /**
   * 根据type与name获得容器中的java类实例
   */
  <T> T getInstance(Class<T> type, String name);

  /**
   * 根据type和默认的name(default)获得容器中的java类实例
   */
  <T> T getInstance(Class<T> type);
 
  /**
   * 根据type获得所有注册这个type的name
   */
  Set<String> getInstanceNames(Class<?> type);

  /**
   * Sets the scope strategy for the current thread.
   */
  void setScopeStrategy(Scope.Strategy scopeStrategy);

  /**
   * Removes the scope strategy for the current thread.
   */
  void removeScopeStrategy();
}

XWork容器的管辖范围

public class Person{
    @Inject
    private Car car;

    public Person(){
    //其他代码
    }
    @Inject
    public void setCar(Car c){
    this.car=c;
    }
    public void drive(){
    car.drive();
    }
}

@Target({METHOD, CONSTRUCTOR, FIELD, PARAMETER})
@Retention(RUNTIME)
public @interface Inject {

  /**
   * Dependency name. Defaults to {@link Container。DEFAULT_NAME}.
   */
  String value() default DEFAULT_NAME;

  /**
   * Whether or not injection is required. Applicable only to methods and
   * fields (not constructors or parameters).
   */
  boolean required() default true;
}

通过容器接口进行对象操作

public class DefaultUnknownHandlerManager implements UnknownHandlerManager {
    protected ArrayList<UnknownHandler> unknownHandlers;
    private Configuration configuration;
    private Container container;

    @Inject
    public void setConfiguration(Configuration configuration) {
        this.configuration = configuration;
        build();
    }

    @Inject
    public void setContainer(Container container) {
        this.container = container;
        build();
    }

    /**
     * Builds a list of UnknowHandlers in the order specified by the configured "unknown-handler-stack".
     * If "unknown-handler-stack" was not configured, all UnknowHandlers will be returned, in no specific order
     */
    protected void build() {
        if (configuration != null && container != null) {
            List<UnknownHandlerConfig> unkownHandlerStack = configuration.getUnknownHandlerStack();
            unknownHandlers = new ArrayList<UnknownHandler>();

            if (unkownHandlerStack != null && !unkownHandlerStack.isEmpty()) {
                //get UnknownHandlers in the specified order
        // 根据一定顺序获取UnknownHandler实例
                for (UnknownHandlerConfig unknownHandlerConfig : unkownHandlerStack) {
            //通过容器的getInstance方法获得容器内部脱光光的type为UnknownHandler.class
            //name为传入的参数的UnknownHandler
                    UnknownHandler uh = container.getInstance(UnknownHandler.class, unknownHandlerConfig.getName());
                    unknownHandlers.add(uh);
                }
            } else {
                //add all available UnknownHandlers
                Set<String> unknowHandlerNames = container.getInstanceNames(UnknownHandler.class);
                for (String unknowHandlerName : unknowHandlerNames) {
                    UnknownHandler uh = container.getInstance(UnknownHandler.class, unknowHandlerName);
                    unknownHandlers.add(uh);
                }
            }
        }
    }
    .....
}

public class ActionSupport implements Action, Validateable, ValidationAware, TextProvider, LocaleProvider, Serializable {

    private TextProvider getTextProvider() {
        if (textProvider == null) {
            TextProviderFactory tpf = new TextProviderFactory();
            if (container != null) {
                container.inject(tpf);
            }
            textProvider = tpf.createInstance(getClass(), this);
        }
        return textProvider;
    }

    @Inject
    public void setContainer(Container container) {
        this.container = container;
    }
}

public class TextProviderFactory {

    private TextProvider textProvider;

    @Inject
    public void setTextProvider(TextProvider textProvider) {
        this.textProvider = textProvider;
    }
    .....
}

参考资料

XWork中的容器1