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, 5 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.
#	User	Rev	Content
1	pjm2	1.1	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	pjm2	1.3	// Construct it if it does not already exist, otherwise just return the reference.
15	pjm2	1.1	public static PluginFilterManager getInstance() throws NotInitialisedException {
16			if (_instance == null){
17	pjm2	1.3	return new PluginFilterManager();
18	pjm2	1.1	}
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	pjm2	1.3	System.out.println("");
28	pjm2	1.1
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	pjm2	1.3	System.out.println("Added filter: "+files[i]+" ("+pf.getDescription()+")");
46	pjm2	1.1	}
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	pjm2	1.3
60			System.out.println("");
61	pjm2	1.1	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	pjm2	1.2	}