server/PluginManager/PluginFilterManager.java

import java.io.*;
import java.util.*;

import uk.ac.ukc.iscream.util.*;

// the plugin filter manager
// This is a singleton class.

// pjm2@ukc.ac.uk

class PluginFilterManager {
    
    // Return a reference to the single class.
    // Construct it if it does not already exist, otherwise just return the reference.
    public static PluginFilterManager getInstance() throws NotInitialisedException {
        if (_instance == null){
            return new PluginFilterManager();
        }
        return _instance;
    }
    
    // Private Constructor - this part creates the filter pipeline
    // This is a singleton class, btw.
    private PluginFilterManager(){
        
        System.out.println("Creating filter pipeline for plugin filters ...");
        System.out.println("");
        
        // Look in the specified directory for "*__Plugin.class" files.
        File file = new File(_directory);
        String[] files = file.list();
        
        // For each "__Plugin.class" file...
        for (int i = 0; i < files.length; i++){
            if (files[i].endsWith(_suffix)){
                
                // Remove the ".class" file extension.
                files[i] = files[i].substring(0, files[i].length() - 6);
                
                // Create an instance of the specified PluginFilter to include
                // within the filterPipe.  Add it to the filterPipeline
                try {
                    PluginFilter pf = (PluginFilter)ClassLoader.getSystemClassLoader().loadClass(files[i]).newInstance();
                    _filterPipeline.add(pf);
                    System.out.println("Added filter: "+files[i]+" ("+pf.getDescription()+")");
                }
                catch (InstantiationException e){
                    System.out.println("Failed to add "+files[i]+" to the plugin filter pipeline.");
                }
                catch (Exception e){
                    System.out.println("Failed to add "+files[i]+" to the plugin filter pipeline.");
                }
                
            }
            else {
                //System.out.println("Ignoring "+files[i]+" in the plugin folder.");
            }
        }

        System.out.println("");        
        System.out.println("The filter pipeline has been set up with "+_filterPipeline.size()+" plugin filters.");
        
    }
    
    
    // apply all of the filters in the pipeline to the packet.
    // return true if they all accept the packet.
    // return false if any single filter rejects the packet.
    // return true if there are no filters inthe pipeline.
    public boolean runFilters(XMLPacket packet){
        
        // for each filter in the pipeline...
        ListIterator pluginFilters = _filterPipeline.listIterator(0);
        while (pluginFilters.hasNext()){
            PluginFilter filter = (PluginFilter)pluginFilters.next();
            if (!filter.runFilter(packet)){
                return false;
            }
        }
        
        return true;
    }
    
    
    // directory storing the plugins:
    private final String _directory = "./";
    
    // file name suffix for plugin filter classes:
    private final String _suffix = "__Plugin.class";
    
    // LinkedList for holding the PluginFilter objects (the pipeline).
    private LinkedList _filterPipeline = new LinkedList();
    
    // A reference to the single instance of this class
    private static PluginFilterManager _instance;
    
}
Revision:	1.3
Committed:	Fri Dec 1 14:38:47 2000 UTC (23 years, 4 months ago) by pjm2
Branch:	MAIN
CVS Tags:	PROJECT_COMPLETION, HEAD
Changes since 1.2:	+6 -13 lines
Log Message:	Altered the PluginFilterManager such that when it successfully adds each plugin filter to the plugin filter pipeline, it prints a description of what each plugin filter does. There is now a single getInstance() method on the PluginFilterManager that returns a reference to itself. If an instance of it does not already exist, then it calls its own private constructor.
#	Content
1	import java.io.*;
2	import java.util.*;
3
4	import uk.ac.ukc.iscream.util.*;
5
6	// the plugin filter manager
7	// This is a singleton class.
8
9	// pjm2@ukc.ac.uk
10
11	class PluginFilterManager {
12
13	// Return a reference to the single class.
14	// Construct it if it does not already exist, otherwise just return the reference.
15	public static PluginFilterManager getInstance() throws NotInitialisedException {
16	if (_instance == null){
17	return new PluginFilterManager();
18	}
19	return _instance;
20	}
21
22	// Private Constructor - this part creates the filter pipeline
23	// This is a singleton class, btw.
24	private PluginFilterManager(){
25
26	System.out.println("Creating filter pipeline for plugin filters ...");
27	System.out.println("");
28
29	// Look in the specified directory for "*__Plugin.class" files.
30	File file = new File(_directory);
31	String[] files = file.list();
32
33	// For each "__Plugin.class" file...
34	for (int i = 0; i < files.length; i++){
35	if (files[i].endsWith(_suffix)){
36
37	// Remove the ".class" file extension.
38	files[i] = files[i].substring(0, files[i].length() - 6);
39
40	// Create an instance of the specified PluginFilter to include
41	// within the filterPipe. Add it to the filterPipeline
42	try {
43	PluginFilter pf = (PluginFilter)ClassLoader.getSystemClassLoader().loadClass(files[i]).newInstance();
44	_filterPipeline.add(pf);
45	System.out.println("Added filter: "+files[i]+" ("+pf.getDescription()+")");
46	}
47	catch (InstantiationException e){
48	System.out.println("Failed to add "+files[i]+" to the plugin filter pipeline.");
49	}
50	catch (Exception e){
51	System.out.println("Failed to add "+files[i]+" to the plugin filter pipeline.");
52	}
53
54	}
55	else {
56	//System.out.println("Ignoring "+files[i]+" in the plugin folder.");
57	}
58	}
59
60	System.out.println("");
61	System.out.println("The filter pipeline has been set up with "+_filterPipeline.size()+" plugin filters.");
62
63	}
64
65
66	// apply all of the filters in the pipeline to the packet.
67	// return true if they all accept the packet.
68	// return false if any single filter rejects the packet.
69	// return true if there are no filters inthe pipeline.
70	public boolean runFilters(XMLPacket packet){
71
72	// for each filter in the pipeline...
73	ListIterator pluginFilters = _filterPipeline.listIterator(0);
74	while (pluginFilters.hasNext()){
75	PluginFilter filter = (PluginFilter)pluginFilters.next();
76	if (!filter.runFilter(packet)){
77	return false;
78	}
79	}
80
81	return true;
82	}
83
84
85	// directory storing the plugins:
86	private final String _directory = "./";
87
88	// file name suffix for plugin filter classes:
89	private final String _suffix = "__Plugin.class";
90
91	// LinkedList for holding the PluginFilter objects (the pipeline).
92	private LinkedList _filterPipeline = new LinkedList();
93
94	// A reference to the single instance of this class
95	private static PluginFilterManager _instance;
96
97	}