Throw a build exception if a public constructor that takes in a Reader as its

sole argument is absent.

PR: 20768


git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@274673 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/filters/util/ChainReaderHelper.java

@@ -185,14 +185,21 @@ public final class ChainReaderHelper {
                                 final Constructor[] constructors =
                                     clazz.getConstructors();
                                 int j = 0;
+                                boolean consPresent = false;
                                 for (; j < constructors.length; j++) {
                                     Class[] types = constructors[j]
                                                       .getParameterTypes();
                                     if (types.length == 1 &&
                                         types[0].isAssignableFrom(Reader.class)) {
+                                        consPresent = true;
                                         break;
                                     }
                                 }
+                                if ( !consPresent ) {
+                                    throw new BuildException( className +
+                                            " does not define a public constructor" +
+                                            " that takes in a Reader as its single argument.");
+                                }
                                 final Reader[] rdr = {instream};
                                 instream =
                                     (Reader) constructors[j].newInstance(rdr);