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 $

     * instance is <code>true</code>
     * @throws Exception if and error occurs in the looked-up Command.
     */
    public boolean execute(Context context) throws Exception {


        Command command = getCommand(context);
        if (command != null) {
            boolean result = (command.execute(context));
            if (isIgnoreExecuteResult()) {
                return false;
            }
            return result;
        } else {

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     * unless the <code>optional</code> property is <code>false</code>, in which
     * case <code>IllegalArgumentException</code> will be thrown.
     */
    public boolean postprocess(Context context, Exception exception) {


        Command command = getCommand(context);
        if (command != null) {
            if (command instanceof Filter) {
                boolean result = (((Filter) command).postprocess(context, exception));
                if (isIgnorePostprocessResult()) {
                    return false;

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                throw new IllegalArgumentException
                    ("Cannot find catalog '" + catalogName + "'");
            }
        }


        Command command = null;
        String name = getName();
        if (name == null) {
            name = (String) context.get(getNameKey());
        }
        if (name != null) {

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            throw new IllegalStateException(
                "Neither 'method' nor 'methodKey' properties are defined "
            );
        }


        Command command = getCommand(context);


        if (command != null) {
            Method methodObject = extractMethod(command, context);
            Object obj = methodObject.invoke(command, getArguments(context));
            Boolean result = (Boolean)obj;

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        // Check overall command count
        load(DEFAULT_XML);
        checkCommandCount(17);


        // Check individual single command instances
        Command command = null;


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

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        // Check overall command count
        load(DEFAULT_XML);
        checkCommandCount(17);


        // Check individual single command instances
        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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        // Execute the specified command
        try {
            Catalog catalog = (Catalog)
                context.get(getCatalogKey());
            Command command = catalog.getCommand(getExceptionCommand());
            if (log.isTraceEnabled()) {
                log.trace("Calling handler command '" + getExceptionCommand()
                          + "'");
            }
            command.execute(context);
        } catch (Exception e) {
            log.warn("Exception from handler command '" +
                     getExceptionCommand() + "'", e);
            throw new IllegalStateException("Exception chain threw exception");
        }

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                    this.servlet);
        context.put(Constants.MODULE_CONFIG_KEY,
                    this.moduleConfig);


        // Create and execute the command.
        Command command = this.catalog.getCommand("servlet-standard");
        try {
            if (log.isDebugEnabled()) {
                log.debug("Using processing chain for this request");
            }
            command.execute(context);
        } catch (Exception e) {
            // Execute the exception processing chain??
            throw new ServletException(e);
        }

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