src/dolda/jsvc/SvcConfig.java

   1 package dolda.jsvc;
   2
   3 import java.util.*;
   4
   5 public class SvcConfig {
   6     public static class Param<T> {
   7         private T value;
   8         private final Object id = new Object();
   9
  10         public Param(T def) {
  11             this.value = def;
  12         }
  13
  14         @SuppressWarnings("unchecked")
  15         public T get() {
  16             if(Thread.currentThread() instanceof RequestThread) {
  17                 Map<Object, Object> props = RequestThread.request().props();
  18                 if(props.containsKey(id)) {
  19                     /* This can very well actually be set to something
  20                      * of the wrong type, but since the result would,
  21                      * obviously, be a ClassCastException either way,
  22                      * this way is at least the more convenient. */
  23                     return((T)props.get(id));
  24                 }
  25             }
  26             return(value);
  27         }
  28     }
  29
  30     public static Responder let(final Responder next, Object... params) {
  31         final Map<Param, Object> values = new HashMap<Param, Object>();
  32         if((params.length % 2) != 0)
  33             throw(new IllegalArgumentException("SvcConfig.let takes only an even number of parameters"));
  34         for(int i = 0; i < params.length; i += 2)
  35             values.put((Param)params[i], params[i + 1]);
  36         return(new Responder() {
  37                 public void respond(Request req) {
  38                     final Map<Param, Object> old = new HashMap<Param, Object>();
  39                     {
  40                         Map<Object, Object> props = req.props();
  41                         for(Map.Entry<Param, Object> val : values.entrySet()) {
  42                             Param p = val.getKey();
  43                             if(props.containsKey(p.id))
  44                                 old.put(p, props.get(p.id));
  45                             props.put(p.id, val.getValue());
  46                         }
  47                     }
  48                     try {
  49                         next.respond(req);
  50                     } finally {
  51                         Map<Object, Object> props = req.props();
  52                         for(Map.Entry<Param, Object> val : values.entrySet()) {
  53                             Param p = val.getKey();
  54                             if(old.containsKey(p)) {
  55                                 props.put(p.id, old.get(p));
  56                             } else {
  57                                 props.remove(p.id);
  58                             }
  59                         }
  60                     }
  61                 }
  62             });
  63     }
  64 }