componenthelper.java

java ant的源码！非常值得看的源码

            ? null : (String) antLibStack.peek();
    }

    /**
     * Load ant's tasks.
     */
    private void initTasks() {
        ClassLoader classLoader = getClassLoader(null);
        Properties props = getDefaultDefinitions(false);
        Enumeration e = props.propertyNames();
        while (e.hasMoreElements()) {
            String name = (String) e.nextElement();
            String className = props.getProperty(name);
            AntTypeDefinition def = new AntTypeDefinition();
            def.setName(name);
            def.setClassName(className);
            def.setClassLoader(classLoader);
            def.setAdaptToClass(Task.class);
            def.setAdapterClass(TaskAdapter.class);
            antTypeTable.put(name, def);
        }
    }

    private ClassLoader getClassLoader(ClassLoader classLoader) {
        String buildSysclasspath = project.getProperty(MagicNames.BUILD_SYSCLASSPATH);
        if (project.getCoreLoader() != null
            && !(BUILD_SYSCLASSPATH_ONLY.equals(buildSysclasspath))) {
            classLoader = project.getCoreLoader();
        }
        return classLoader;
    }

    /**
     * Load default task or type definitions - just the names,
     *  no class loading.
     * Caches results between calls to reduce overhead.
     * @param type true for typedefs, false for taskdefs
     * @return a mapping from definition names to class names
     * @throws BuildException if there was some problem loading
     *                        or parsing the definitions list
     */
    private static synchronized Properties getDefaultDefinitions(boolean type)
        throws BuildException {
        int idx = type ? 1 : 0;
        if (defaultDefinitions[idx] == null) {
            String resource = type
                ? MagicNames.TYPEDEFS_PROPERTIES_RESOURCE
                : MagicNames.TASKDEF_PROPERTIES_RESOURCE;
            String errorString = type
                ? ERROR_NO_TYPE_LIST_LOAD
                : ERROR_NO_TASK_LIST_LOAD;
            InputStream in = null;
            try {
                in = ComponentHelper.class.getResourceAsStream(
                    resource);
                if (in == null) {
                    throw new BuildException(errorString);
                }
                Properties p = new Properties();
                p.load(in);
                defaultDefinitions[idx] = p;
            } catch (IOException e) {
                throw new BuildException(errorString, e);
            } finally {
                FileUtils.close(in);
            }
        }
        return defaultDefinitions[idx];
    }

    /**
     * Load ant's datatypes.
     */
    private void initTypes() {
        ClassLoader classLoader = getClassLoader(null);
        Properties props = getDefaultDefinitions(true);
        Enumeration e = props.propertyNames();
        while (e.hasMoreElements()) {
            String name = (String) e.nextElement();
            String className = props.getProperty(name);
            AntTypeDefinition def = new AntTypeDefinition();
            def.setName(name);
            def.setClassName(className);
            def.setClassLoader(classLoader);
            antTypeTable.put(name, def);
        }
    }

    /**
     * Called for each component name, check if the
     * associated URI has been examined for antlibs.
     */
    private synchronized void checkNamespace(String componentName) {
        String uri = ProjectHelper.extractUriFromComponentName(componentName);
        if ("".equals(uri)) {
            uri = ProjectHelper.ANT_CORE_URI;
        }
        if (!uri.startsWith(ProjectHelper.ANTLIB_URI)) {
            return; // namespace that does not contain antlib
        }
        if (checkedNamespaces.contains(uri)) {
            return; // Already processed
        }
        checkedNamespaces.add(uri);
        Typedef definer = new Typedef();
        definer.setProject(project);
        definer.init();
        definer.setURI(uri);
        //there to stop error messages being "null"
        definer.setTaskName(uri);
        //if this is left out, bad things happen. like all build files break
        //on the first element encountered.
        definer.setResource(Definer.makeResourceFromURI(uri));
        // a fishing expedition :- ignore errors if antlib not present
        definer.setOnError(new Typedef.OnError(Typedef.OnError.POLICY_IGNORE));
        definer.execute();
    }

    /**
     * Handler called to do decent diagnosis on instantiation failure.
     * @param componentName component name.
     * @param type component type, used in error messages
     * @return a string containing as much diagnostics info as possible.
     */
    public String diagnoseCreationFailure(String componentName, String type) {
        StringWriter errorText = new StringWriter();
        PrintWriter out = new PrintWriter(errorText);
        out.println("Problem: failed to create " + type + " " + componentName);
        //class of problem
        boolean lowlevel = false;
        boolean jars = false;
        boolean definitions = false;
        boolean antTask;
        String home = System.getProperty(Launcher.USER_HOMEDIR);
        File libDir = new File(home, Launcher.USER_LIBDIR);
        String antHomeLib;
        boolean probablyIDE = false;
        String anthome = System.getProperty(MagicNames.ANT_HOME);
        if (anthome != null) {
            File antHomeLibDir = new File(anthome, "lib");
            antHomeLib = antHomeLibDir.getAbsolutePath();
        } else {
            //running under an IDE that doesn't set ANT_HOME
            probablyIDE = true;
            antHomeLib = "ANT_HOME" + File.separatorChar + "lib";
        }
        StringBuffer dirListingText = new StringBuffer();
        final String tab = "        -";
        dirListingText.append(tab);
        dirListingText.append(antHomeLib);
        dirListingText.append('\n');
        if (probablyIDE) {
            dirListingText.append(tab);
            dirListingText.append("the IDE Ant configuration dialogs");
        } else {
            dirListingText.append(tab);
            dirListingText.append(libDir);
            dirListingText.append('\n');
            dirListingText.append(tab);
            dirListingText.append(
                    "a directory added on the command line with the -lib argument");
        }

        String dirListing = dirListingText.toString();

        //look up the name
        AntTypeDefinition def = getDefinition(componentName);
        if (def == null) {
            //not a known type
            boolean isAntlib = componentName.indexOf(MagicNames.ANTLIB_PREFIX) == 0;
            out.println("Cause: The name is undefined.");
            out.println("Action: Check the spelling.");
            out.println("Action: Check that any custom tasks/types have been declared.");
            out.println("Action: Check that any <presetdef>/<macrodef>"
                        + " declarations have taken place.");
            if (isAntlib) {
                out.println();
                out.println("This appears to be an antlib declaration. ");
                out.println("Action: Check that the implementing library exists in one of:");
                out.println(dirListing);
            }
            definitions = true;
        } else {
            //we are defined, so it is an instantiation problem
            final String classname = def.getClassName();
            antTask = classname.startsWith("org.apache.tools.ant.");
            boolean optional = classname.startsWith("org.apache.tools.ant.taskdefs.optional");
            optional |= classname.startsWith("org.apache.tools.ant.types.optional");

            //start with instantiating the class.
            Class clazz = null;
            try {
                clazz = def.innerGetTypeClass();
            } catch (ClassNotFoundException e) {
                out.println("Cause: the class " + classname + " was not found.");
                jars = true;
                if (optional) {
                    out.println("        This looks like one of Ant's optional components.");
                    out.println("Action: Check that the appropriate optional JAR exists in");
                    out.println(dirListing);
                } else {
                    out.println("Action: Check that the component has been correctly declared");
                    out.println("        and that the implementing JAR is in one of:");
                    out.println(dirListing);
                    definitions = true;
                }
            } catch (NoClassDefFoundError ncdfe) {
                jars = true;
                out.println("Cause: Could not load a dependent class "
                        +  ncdfe.getMessage());
                if (optional) {
                    out.println("       It is not enough to have Ant's optional JARs");
                    out.println("       you need the JAR files that the"
                                + " optional tasks depend upon.");
                    out.println("       Ant's optional task dependencies are"
                                + " listed in the manual.");
                } else {
                    out.println("       This class may be in a separate JAR"
                                + " that is not installed.");
                }
                out.println("Action: Determine what extra JAR files are"
                            + " needed, and place them in one of:");
                out.println(dirListing);
            }
            //here we successfully loaded the class or failed.
            if (clazz != null) {
                //success: proceed with more steps
                try {
                    def.innerCreateAndSet(clazz, project);
                    //hey, there is nothing wrong with us
                    out.println("The component could be instantiated.");
                } catch (NoSuchMethodException e) {
                    lowlevel = true;
                    out.println("Cause: The class " + classname
                            + " has no compatible constructor.");

                } catch (InstantiationException e) {
                    lowlevel = true;
                    out.println("Cause: The class " + classname
                            + " is abstract and cannot be instantiated.");
                } catch (IllegalAccessException e) {
                    lowlevel = true;
                    out.println("Cause: The constructor for " + classname
                            + " is private and cannot be invoked.");
                } catch (InvocationTargetException ex) {
                    lowlevel = true;
                    Throwable t = ex.getTargetException();
                    out.println("Cause: The constructor threw the exception");
                    out.println(t.toString());
                    t.printStackTrace(out);
                }  catch (NoClassDefFoundError ncdfe) {
                    jars = true;
                    out.println("Cause:  A class needed by class "
                            + classname + " cannot be found: ");
                    out.println("       " + ncdfe.getMessage());
                    out.println("Action: Determine what extra JAR files are"
                                + " needed, and place them in:");
                    out.println(dirListing);
                }
            }
            out.println();
            out.println("Do not panic, this is a common problem.");
            if (definitions) {
                out.println("It may just be a typographical error in the build file "
                        + "or the task/type declaration.");
            }
            if (jars) {
                out.println("The commonest cause is a missing JAR.");
            }
            if (lowlevel) {
                out.println("This is quite a low level problem, which may need "
                        + "consultation with the author of the task.");
                if (antTask) {
                    out.println("This may be the Ant team. Please file a "
                            + "defect or contact the developer team.");
                } else {
                    out.println("This does not appear to be a task bundled with Ant.");
                    out.println("Please take it up with the supplier of the third-party "
                            + type + ".");
                    out.println("If you have written it yourself, you probably have a bug to fix.");
                }
            } else {
                out.println();
                out.println("This is not a bug; it is a configuration problem");
            }
        }
        out.flush();
        out.close();
        return errorText.toString();
    }

    /**
     * Map that contains the component definitions.
     */
    private static class AntTypeTable extends Hashtable {
        private Project project;

        AntTypeTable(Project project) {
            this.project = project;
        }

        AntTypeDefinition getDefinition(String key) {
            return (AntTypeDefinition) (super.get(key));
        }

        public Object get(Object key) {
            return getTypeClass((String) key);
        }

        Object create(String name) {
            AntTypeDefinition def = getDefinition(name);
            return (def == null) ? null : def.create(project);
        }

        Class getTypeClass(String name) {
            AntTypeDefinition def = getDefinition(name);
            return (def == null) ? null : def.getTypeClass(project);
        }

        Class getExposedClass(String name) {
            AntTypeDefinition def = getDefinition(name);
            return (def == null) ? null : def.getExposedClass(project);
        }

        public boolean contains(Object clazz) {
            boolean found = false;
            if (clazz instanceof Class) {
                for (Iterator i = values().iterator(); i.hasNext() && !found;) {
                    found |= (((AntTypeDefinition) (i.next())).getExposedClass(
                        project) == clazz);
                }
            }
            return found;
        }

        public boolean containsValue(Object value) {
            return contains(value);
        }
    }

}