Examples of org.apache.commons.chain.Command

org.apache.commons.chain.Command
A {@link Command} encapsulates a unit of processing work to beperformed, whose purpose is to examine and/or modify the state of a transaction that is represented by a {@link Context}. Individual {@link Command}s can be assembled into a {@link Chain}, which allows them to either complete the required processing or delegate further processing to the next {@link Command} in the {@link Chain}.

{@link Command} implementations should be designed in a thread-safemanner, suitable for inclusion in multiple {@link Chain}s that might be processed by different threads simultaneously. In general, this implies that {@link Command} classes should not maintain state information ininstance variables. Instead, state information should be maintained via suitable modifications to the attributes of the {@link Context} that ispassed to the execute() command.

{@link Command} implementations typically retrieve and store stateinformation in the {@link Context} instance that is passed as a parameterto the execute() method, using particular keys into the Map that can be acquired via Context.getAttributes(). To improve interoperability of {@link Command} implementations, a useful design pattern is to expose thekey values used as JavaBeans properties of the {@link Command}implementation class itself. For example, a {@link Command} that requiresan input and an output key might implement the following properties:
```
 private String inputKey = "input"; public String getInputKey() { return (this.inputKey); } public void setInputKey(String inputKey) { this.inputKey = inputKey; } private String outputKey = "output"; public String getOutputKey() { return (this.outputKey); } public void setOutputKey(String outputKey) { this.outputKey = outputKey; } 
```
And the operation of accessing the "input" information in the context would be executed by calling:
```
 String input = (String) context.get(getInputKey()); 
```
instead of hard coding the attribute name. The use of the "Key" suffix on such property names is a useful convention to identify properties being used in this fashion, as opposed to JavaBeans properties that simply configure the internal operation of this {@link Command}.
@author Craig R. McClanahan @version $Revision: 1.5 $ $Date: 2004/02/25 00:01:07 $


        actionCtx.setException(exception);


        // Execute the specified command
        try {
            Command command = lookupExceptionCommand();


            if (command == null) {
                LOG.error("Cannot find exceptionCommand '" + exceptionCommand
                    + "'");
                throw new IllegalStateException(
                    "Cannot find exceptionCommand '" + exceptionCommand + "'");
            }


            if (LOG.isTraceEnabled()) {
                LOG.trace("Calling exceptionCommand '" + exceptionCommand + "'");
            }


            command.execute(context);
        } catch (Exception e) {
            LOG.warn("Exception from exceptionCommand '" + exceptionCommand
                + "'", e);
            throw new IllegalStateException("Exception chain threw exception");
        }

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        throws Exception {
        if (LOG.isTraceEnabled()) {
            LOG.trace("execute [" + this + "]");
        }


        Command command = getCommand(context);


        if (command != null) {
            return command.execute(getContext(context));
        } else {
            return false;
        }
    }

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     * @param context   Our ActionContext
     * @param exception The Exception thrown by another Comamnd in a Chain
     * @return TRUE if there is a Filter to process
     */
    public boolean postprocess(Context context, Exception exception) {
        Command command = getCommand(context);


        if ((command != null) && (command instanceof Filter)) {
            try {
                return ((Filter) command).postprocess(getContext(context),
                    exception);

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        if (catalog == null) {
            throw new IllegalArgumentException("Cannot find catalog '"
                + catalogName + "'");
        }


        Command command;
        String name = getName();


        if (name == null) {
            name = (String) context.get(getNameKey());
        }

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     * @throws Exception on any error
     */
    public boolean execute(ActionContext actionCtx)
        throws Exception {
        if (shouldProcess(actionCtx)) {
            Command command = getCommand(actionCtx);


            if (command != null) {
                return (command.execute(actionCtx));
            }
        }


        return (false);
    }

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    // Test getting commands
    public void testGetCommand() {


        addCommands();
        Command command = null;


        command = catalog.getCommand("AddingCommand");
        assertNotNull(command);
        assertTrue(command instanceof AddingCommand);

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    // Test the ability to add commands
    public void testCommands() {


        checkCommandCount(0);


        Command command1 = new NonDelegatingCommand("1");
        chain.addCommand(command1);
        checkCommandCount(1);


        Command command2 = new DelegatingCommand("2");
        chain.addCommand(command2);
        checkCommandCount(2);


        Command command3 = new ExceptionCommand("3");
        chain.addCommand(command3);
        checkCommandCount(3);


    }

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    // Verify the number of configured commands
    protected void checkCommandCount(int expected) {
        if (chain instanceof ChainBase) {
            Command commands[] = ((ChainBase) chain).getCommands();
            assertNotNull("getCommands() returned a non-null array",
                          commands);
            assertEquals("Correct command count", expected, commands.length);
        }
    }

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        Object top = digester.peek(0);
        if ((top == null)
            || !(top instanceof Command)) {
            return;
        }
        Command command = (Command) top;


        // Is the next object a Catalog or a Chain?
        Object next = digester.peek(1);
        if (next == null) {
            return;

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            servletPath = request.getServletPath();
        }


        // Map to the Command specified by the extra path info
        Catalog catalog = (Catalog) context.get(getCatalogKey());
        Command command = catalog.getCommand(servletPath);
        return (command.execute(context));


    }

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