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Using the Examples in Applets (Java Distributed Computing)
Table of Contents
Appendix A. Using the Examples in Applets....................................................................................................1
A.1. Whiteboard Applet........................................................................................................................................1
A.2. Class Downloads...........................................................................................................................................6
Appendix B. CORBA Services...........................................................................................................................7
B.1. Naming Service.............................................................................................................................................7
B.1.1. Comparison to the RMI Registry...............................................................................................................8
B.2. Event Service.................................................................................................................................................9
B.2.1. Quality of Service for Channels...............................................................................................................11
B.2.2. Interface Specifics....................................................................................................................................11
B.2.3. Comparison to the Java Event Model......................................................................................................12
B.3. Security Service...........................................................................................................................................13
B.3.1. Service Types..............................................................................................................................13
B.3.2. Security Model............................................................................................................................14
B.3.3. Comparison to the Java Security API.........................................................................................15
B.4. Other Key CORBA Services.......................................................................................................................16
Appendix C. JavaSpaces..................................................................................................................................17
C.1. Overview of JavaSpaces..............................................................................................................................17
C.2. Entry and EntryRep.....................................................................................................................................19
C.3. Transactions................................................................................................................................................20
C.4. The JavaSpace Interface..............................................................................................................................20
C.4.1. write()..........................................................................................................................................21
C.4.2. read()...........................................................................................................................................21
C.4.3. take()............................................................................................................................................21
C.4.4. notify().........................................................................................................................................21
C.4.5. renew()........................................................................................................................................22
C.4.6. cancel()........................................................................................................................................22
Appendix D. RMI Quick Reference................................................................................................................23
D.1. The java.rmi Package..................................................................................................................................23
D.2. The java.rmi.registry Package.....................................................................................................................29
D.3. The java.rmi.server Package.......................................................................................................................31
Preface................................................................................................................................................................40
0.1. What Does This Book Cover?........................................................................................................41
0.1.1. Organization....................................................................................................................41
0.2. Who Should Read This Book?........................................................................................................42
0.3. About the Source Code...................................................................................................................43
0.4. Conventions Used in This Book.....................................................................................................44
0.5. Acknowledgments...........................................................................................................................45
1.1. Anatomy of a Distributed Application............................................................................................46
1.2. Requirements for Developing Distributed Applications.................................................................47
1.2.1. Partitioning and Distributing Data and Functions..........................................................48
1.2.2. Flexible, Extendible Communication Protocols.............................................................48
1.2.3. Multithreading Requirements.........................................................................................49
1.2.4. Security Issues................................................................................................................49
1.3. What Does Java Provide?...............................................................................................................49
1.3.1. Object−Oriented Environment........................................................................................50
1.3.2. Abstract Interfaces..........................................................................................................50
1.3.3. Platform Independence...................................................................................................51
1.3.4. Fault Tolerance Through Exception Handling...............................................................51
Using the Examples in Applets (Java Distributed Computing)
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Table of Contents
Preface
1.3.5. Network Support.............................................................................................................51
1.3.6. Security...........................................................................................................................52
1.3.6.1. Runtime environment..................................................................................................58
1.3.6.2. Secure remote transactions..........................................................................................59
1.3.7. Multithreading Support...................................................................................................59
2.1. Sockets and Streams.......................................................................................................................60
2.1.1. IP Addressing..................................................................................................................62
2.1.2. Your Basic Socket..........................................................................................................62
2.1.3. Multicast Sockets............................................................................................................62
2.1.4. Streams, Readers, and Writers for Input and Output......................................................63
2.2.1. When and Where Are URLs Practical?..........................................................................64
2.2. URLs, URLConnections, and ContentHandlers.............................................................................65
2.3. The ClassLoader.............................................................................................................................72
2.3.1. Loading Classes from the Network................................................................................74
3.1. Why Distribute Objects?.................................................................................................................74
3.2. What's So Tough About Distributing Objects?...............................................................................75
3.2.1. Creating Remote Objects................................................................................................80
3.2.2. Remote Method Calls.....................................................................................................80
3.2.3. Other Issues.....................................................................................................................81
3.3.1. Object Interface Specification........................................................................................81
3.3.2. Object Manager...............................................................................................................82
3.3.3. Registration/Naming Service..........................................................................................84
3.3.4. Object Communication Protocol....................................................................................85
3.3.5. Development Tools.........................................................................................................86
3.3.6. Security...........................................................................................................................87
3.3. Features of Distributed Object Systems..........................................................................................87
3.4. Distributed Object Schemes for Java..............................................................................................87
3.5. CORBA...........................................................................................................................................88
3.5.1. The Object Request Broker (ORB).................................................................................88
3.5.2. The Interface Definition Language (IDL)......................................................................88
3.5.3. Server Implementations..................................................................................................90
3.5.4. Client Stubs.....................................................................................................................91
3.5.5. A CORBA Solver...........................................................................................................91
3.5.5.1. The IDL interface.........................................................................................................92
3.5.5.2. The client stubs............................................................................................................93
3.5.5.3. The server skeleton and implementation.....................................................................93
3.5.5.4. The Solver client..........................................................................................................93
3.5.5.5. Pulling it all together....................................................................................................94
3.6. Java RMI.........................................................................................................................................96
3.6.1. Remote Object Interfaces................................................................................................99
3.6.2. Server Implementations..................................................................................................99
3.6.3. The RMI Registry.........................................................................................................100
3.6.4. Client Stubs and Server Skeletons................................................................................101
3.6.5. Registering and Using a Remote Object.......................................................................101
3.6.6. Serializing Objects........................................................................................................101
3.6.7. An RMI Solver..............................................................................................................102
3.7. RMI vs. CORBA...........................................................................................................................102
3.7.1. The Language Barrier: Advantage or Disadvantage?...................................................103
3.7.2. Other Differences..........................................................................................................103
3.7.3. The Bottom Line...........................................................................................................108
4.1. Thread and Runnable....................................................................................................................109
Using the Examples in Applets (Java Distributed Computing)
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Table of Contents
Preface
4.2. Making a Thread...........................................................................................................................109
4.2.1. Implementing Runnable................................................................................................110
4.2.2. Extending Thread..........................................................................................................111
4.3. Managing Threads at Runtime......................................................................................................111
4.3.1. Synchronizing Threads.................................................................................................112
4.3.2. Thread Groups..............................................................................................................112
4.3.3. Priorities........................................................................................................................117
4.4. Networked Threads.......................................................................................................................117
4.4.1. Asynchronous Agents...................................................................................................117
4.4.2. Distributed ThreadGroups............................................................................................118
4.4.3. Improving Efficiency with Thread Priorities................................................................118
4.4.4. Synchronizing Distributed Threads..............................................................................119
5.1. Security Issues and Concerns........................................................................................................119
5.2. The java.security Package.............................................................................................................120
5.2.1. Architectural Overview.................................................................................................123
5.2.1.1. The User API.............................................................................................................124
5.2.1.2. The Provider API.......................................................................................................126
5.2.2. The Core Security API..................................................................................................126
5.3. Identities and Access Control.......................................................................................................128
5.3.1. Access Control Lists.....................................................................................................128
5.4. Keys: Public, Private, and Secret..................................................................................................128
5.4.1. Secret Keys...................................................................................................................129
5.4.2. Public Key Methods......................................................................................................129
5.4.3. Keys in the Java Security API......................................................................................132
5.5. Digital Signatures.........................................................................................................................133
5.5.1. A Motivating Example: A Credit Agent.......................................................................135
5.5.2. Public Key Signatures for Authentication....................................................................135
5.5.3. An Authenticating Credit Agent...................................................................................135
5.5.4. Certification: The Last Identity Link............................................................................136
5.5.5. Distributing Certified Public Keys...............................................................................137
5.6. Data Encryption............................................................................................................................138
5.6.1. Ciphers for Secure Data Transfers................................................................................139
5.6.2. Back to Our Credit Agent.............................................................................................140
5.7. Choosing a Cryptographic Algorithm...........................................................................................143
5.7.1. Features of Cryptographic Algorithms.........................................................................143
5.7.1.1. Level of protection.....................................................................................................144
5.7.1.2. Sophistication and complexity...................................................................................145
5.7.1.3. One−, two−, and many−way cryptography...............................................................145
5.7.1.4. Design issues..............................................................................................................149
5.7.1.5. Financial and legal issues..........................................................................................149
5.7.2. Available Algorithms....................................................................................................149
5.7.2.1. Encryption techniques................................................................................................149
5.7.2.2. Certificates and authentication techniques................................................................149
5.7.3. General Security Protocols...........................................................................................150
5.7.3.1. Secure Socket Layer (SSL)........................................................................................150
5.7.3.2. Pretty Good Privacy (PGP)........................................................................................150
6.1. Messages Defined.........................................................................................................................151
6.2. Why Do We Need Messages?.......................................................................................................151
6.3. Message Processing......................................................................................................................151
6.3.1. Asychronous vs. Synchronous Message Handling.......................................................152
6.3.2. A Basic Message Processor..........................................................................................152
Using the Examples in Applets (Java Distributed Computing)
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Preface
6.4.1. Heterogeneous Argument Lists....................................................................................154
6.4.2. Objects as Message Arguments....................................................................................154
6.4. Fixed Protocols.............................................................................................................................155
6.5. Adaptable Protocols......................................................................................................................156
6.5.1. Variable Number of Arguments...................................................................................156
6.5.2. Variable Message Argument Types..............................................................................157
6.5.3. Adaptable Message Types............................................................................................160
6.5.4. An Adaptable Message Handler...................................................................................167
6.6. Message Passing with Java Events...............................................................................................171
6.6.1. Event Model Overview.................................................................................................173
6.6.2. Distributed Events.........................................................................................................174
6.6.3. Pros and Cons...............................................................................................................174
6.7. Using Remote Objects..................................................................................................................174
7.1. An Overview of JDBC..................................................................................................................174
7.1.1. Data Retrieval Example................................................................................................181
7.1.2. The API at a Glance......................................................................................................181
7.1.2.1. DriverManager...........................................................................................................181
7.1.2.2. Connection.................................................................................................................187
7.1.2.3. Statement...................................................................................................................189
7.1.2.4. ResultSet....................................................................................................................194
7.2.1. JDBC Driver Configurations........................................................................................194
7.2.2. Defining the Data Objects.............................................................................................194
7.2.3. A Scheduling Example.................................................................................................195
7.2.4. JDBC−Enabled Data Objects.......................................................................................195
7.2.5. Data Caching Issues......................................................................................................196
7.2.6. Remote Data Servers....................................................................................................196
7.2.6.1. Message passing with the data server........................................................................197
7.2.6.2. Distributed objects from the data server....................................................................198
7.2. Remote Database Applications.....................................................................................................198
7.3. Multi−Database Applications.......................................................................................................200
8.1. Flavors of Limited Bandwidth......................................................................................................200
8.2. Coping with Limited Bandwidth..................................................................................................202
8.2.1. Monitoring Bandwidth..................................................................................................210
8.2.2. Managing Bandwidth....................................................................................................211
8.2.3. Levels of Monitoring and Management........................................................................211
8.4.1. Raw Data Monitoring...................................................................................................213
8.4.2. Real Data Monitoring...................................................................................................221
8.3. Scope of This Chapter...................................................................................................................224
8.4. Monitoring Bandwidth..................................................................................................................224
8.5. Bandwidth Management...............................................................................................................225
8.5.1. Streaming Multimedia..................................................................................................225
8.5.2. Web Browsing..............................................................................................................225
9.1. What Is a Collaborative System?..................................................................................................226
9.2. Issues with Collaboration..............................................................................................................226
9.2.1. Communication Needs..................................................................................................227
9.2.2. Maintaining Agent Identities........................................................................................229
9.2.3. Shared State Information..............................................................................................232
9.2.4. Performance..................................................................................................................237
9.3. A Basic Collaborative Infrastructure............................................................................................237
9.3.1. Building the Infrastructure with Message Passing.......................................................242
9.3.2. Collaborating with RMI................................................................................................247
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