Provide a mechanism by which filter readers recognized by Ant's core (FilterreaderSet can have a better syntax.

For example, HeadFilter can be added to filterset as this:

<filterreaderset>
  <filterreader classname="org.apache.tools.ant.HeadFilter">
    <param name="lines" value="3"/>
  </filterreader>
</filterreaderset>

or this:

<filterreaderset>
  <headfilter lines="3"/>
</filterreaderset>


git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@271580 13f79535-47bb-0310-9956-ffa450edef68

proposal/sandbox/filterreaders/src/main/org/apache/tools/ant/filters/CloneableReader.java

@@ -0,0 +1,7 @@
+package org.apache.tools.ant.filters;
+
+import java.io.Reader;
+
+public interface CloneableReader {
+    public Reader clone(Reader rdr);
+}

proposal/sandbox/filterreaders/src/main/org/apache/tools/ant/filters/HeadFilter.java

@@ -56,6 +56,7 @@ package org.apache.tools.ant.filters;
 import java.io.FilterReader;
 import java.io.IOException;
 import java.io.Reader;
+import java.io.StringReader;
 
 import org.apache.tools.ant.types.Parameter;
 import org.apache.tools.ant.types.Parameterizable;
@@ -66,6 +67,10 @@ import org.apache.tools.ant.types.Parameterizable;
  * Example:
  * =======
  *
+ * <headfilter lines="3"/>
+ *
+ * Or:
+ *
  * <filterreader classname="org.apache.tools.ant.filters.HeadFilter">
  *    <param name="lines" value="3"/>
  * </filterreader>
@@ -74,7 +79,7 @@ import org.apache.tools.ant.types.Parameterizable;
  */
 public final class HeadFilter
     extends FilterReader
-    implements Parameterizable
+    implements Parameterizable, CloneableReader
 {
     private static final String LINES_KEY = "lines";
 
@@ -88,6 +93,22 @@ public final class HeadFilter
 
     private boolean ignoreLineFeed = false;
 
+    /**
+     * This constructor is a dummy constructor and is
+     * not meant to be used by any class other than Ant's
+     * introspection mechanism. This will close the filter
+     * that is created making it useless for further operations.
+     */
+    public HeadFilter() {
+        // Dummy constructor to be invoked by Ant's Introspector
+        super(new StringReader(new String()));
+        try {
+            close();
+        } catch (IOException  ioe) {
+            // Ignore
+        }
+    }
+
     /**
      * Create a new filtered reader.
      *
@@ -98,9 +119,9 @@ public final class HeadFilter
     }
 
     public final int read() throws IOException {
-        if (!initialized) {
+        if (!getInitialized()) {
             initialize();
-            initialized = true;
+            setInitialized(true);
         }
 
         int ch = -1;
@@ -155,12 +176,35 @@ public final class HeadFilter
         return n;
     }
 
+    public final void setLines(final long lines) {
+        this.lines = lines;
+    }
+
+    public final long getLines() {
+        return lines;
+    }
+
+    public final void setInitialized(final boolean initialized) {
+        this.initialized = initialized;
+    }
+
+    public final boolean getInitialized() {
+        return initialized;
+    }
+
+    public final Reader clone(final Reader rdr) {
+        HeadFilter newFilter = new HeadFilter(rdr);
+        newFilter.setLines(getLines());
+        newFilter.setInitialized(true);
+        return newFilter;
+    }
+
     /**
      * Set Parameters
      */
     public final void setParameters(final Parameter[] parameters) {
         this.parameters = parameters;
-        initialized = false;
+        setInitialized(false);
     }
 
     private final void initialize() {

proposal/sandbox/filterreaders/src/main/org/apache/tools/ant/types/FilterReaderSet.java

@@ -55,6 +55,8 @@ package org.apache.tools.ant.types;
 
 import java.util.Vector;
 
+import org.apache.tools.ant.filters.HeadFilter;
+
 /**
  * Set of FilterReaders
  *
@@ -71,4 +73,8 @@ public final class FilterReaderSet {
     public final Vector getFilterReaders() {
         return filterReaders;
     }
+
+    public final void addHeadFilter(final HeadFilter headFilter) {
+        filterReaders.addElement(headFilter);
+    }
 }

proposal/sandbox/filterreaders/src/main/org/apache/tools/ant/util/ChainReaderHelper.java

@@ -56,6 +56,7 @@ package org.apache.tools.ant.util;
 import org.apache.tools.ant.AntClassLoader;
 import org.apache.tools.ant.BuildException;
 import org.apache.tools.ant.Project;
+import org.apache.tools.ant.filters.CloneableReader;
 import org.apache.tools.ant.types.AntFilterReader;
 import org.apache.tools.ant.types.FilterReaderSet;
 import org.apache.tools.ant.types.Path;
@@ -133,9 +134,7 @@ public final class ChainReaderHelper {
             final Vector filterReaders = filterset.getFilterReaders();
             final int readerCount = filterReaders.size();
             for (int j = 0; j < readerCount; j++) {
-                final AntFilterReader afr =
-                    (AntFilterReader) filterReaders.elementAt(j);
-                finalFilters.addElement(afr);
+                finalFilters.addElement(filterReaders.elementAt(j));
             }
         }
 
@@ -143,47 +142,62 @@ public final class ChainReaderHelper {
 
         if (filtersCount > 0) {
             for (int i = 0; i < filtersCount; i++) {
-                final AntFilterReader filter =
-                    (AntFilterReader) finalFilters.elementAt(i);
-                final String className = filter.getClassName();
-                final Path classpath = filter.getClasspath();
-                final Project project = filter.getProject();
-                if (className != null) {
-                    try {
-                        Class clazz = null;
-                        if (classpath == null) {
-                            clazz = Class.forName(className);
-                        } else {
-                            AntClassLoader al = new AntClassLoader(project,
-                                                                   classpath);
-                            clazz = al.loadClass(className);
-                            AntClassLoader.initializeClass(clazz);
-                        }
-                        if (clazz != null) {
-                            if (!FilterReader.class.isAssignableFrom(clazz)) {
-                                throw new BuildException(className +
-                                    " does not extend java.io.FilterReader");
+                Object o = finalFilters.elementAt(i);
+
+                if (o instanceof AntFilterReader) {
+                    final AntFilterReader filter = (AntFilterReader) finalFilters.elementAt(i);
+                    final String className = filter.getClassName();
+                    final Path classpath = filter.getClasspath();
+                    final Project project = filter.getProject();
+                    if (className != null) {
+                        try {
+                            Class clazz = null;
+                            if (classpath == null) {
+                                clazz = Class.forName(className);
+                            } else {
+                                AntClassLoader al = new AntClassLoader(project,
+                                                                       classpath);
+                                clazz = al.loadClass(className);
+                                AntClassLoader.initializeClass(clazz);
                             }
-                            final Constructor[] constructors =
-                                clazz.getConstructors();
-                            final Reader[] rdr = {instream};
-                            instream =
-                                (Reader) constructors[0].newInstance(rdr);
-                            if (Parameterizable.class.isAssignableFrom(clazz)) {
-                                final Parameter[] params = filter.getParams();
-                                ((Parameterizable)
-                                    instream).setParameters(params);
+                            if (clazz != null) {
+                                if (!FilterReader.class.isAssignableFrom(clazz)) {
+                                    throw new BuildException(className +
+                                        " does not extend java.io.FilterReader");
+                                }
+                                final Constructor[] constructors =
+                                    clazz.getConstructors();
+                                int j = 0;
+                                for (; j < constructors.length; j++) {
+                                    Class[] types = constructors[j]
+                                                      .getParameterTypes();
+                                    if (types.length == 1 &&
+                                        types[0].isAssignableFrom(Reader.class)) {
+                                        break;
+                                    }
+                                }
+                                final Reader[] rdr = {instream};
+                                instream =
+                                    (Reader) constructors[j].newInstance(rdr);
+                                if (Parameterizable.class.isAssignableFrom(clazz)) {
+                                    final Parameter[] params = filter.getParams();
+                                    ((Parameterizable)
+                                        instream).setParameters(params);
+                                }
                             }
+                        } catch (final ClassNotFoundException cnfe) {
+                            throw new BuildException(cnfe);
+                        } catch (final InstantiationException ie) {
+                            throw new BuildException(ie);
+                        } catch (final IllegalAccessException iae) {
+                            throw new BuildException(iae);
+                        } catch (final InvocationTargetException ite) {
+                            throw new BuildException(ite);
                         }
-                    } catch (final ClassNotFoundException cnfe) {
-                        throw new BuildException(cnfe);
-                    } catch (final InstantiationException ie) {
-                        throw new BuildException(ie);
-                    } catch (final IllegalAccessException iae) {
-                        throw new BuildException(iae);
-                    } catch (final InvocationTargetException ite) {
-                        throw new BuildException(ite);
                     }
+                } else if (o instanceof CloneableReader &&
+                           o instanceof Reader) {
+                    instream = ((CloneableReader) o).clone(instream);
                 }
             }
         }