Organize project into a reusable library

* Use `{@code}` in javadocs for maintainability
* Replace some loops with functional code
* Inline some trivial methods
* Create flexible API for reporting type problems
* Create separate ClassUtils for getting class info
* Create separate PublicApi class for defining a public API to be
  analyzed
* Separate analyzer code into its own Apilyzer class that takes a
  provided PublicApi and analyzes it independently of any Maven
  functionality. Separating the reponsibilities of different code
  components makes the code a bit more organized, and testable.

src/main/java/net/revelc/code/apilyzer/Apilyzer.java

@@ -0,0 +1,199 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.revelc.code.apilyzer;
+
+import java.lang.reflect.AnnotatedElement;
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Field;
+import java.lang.reflect.Method;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import java.util.function.Consumer;
+import net.revelc.code.apilyzer.problems.Problem;
+import net.revelc.code.apilyzer.problems.ProblemReporter;
+import net.revelc.code.apilyzer.util.ClassUtils;
+
+/**
+ * The entry point to this library.
+ */
+public class Apilyzer {
+
+  private final ProblemReporter problemReporter;
+  private final PatternSet allowsPs;
+  private final boolean ignoreDeprecated;
+  private final PublicApi publicApi;
+
+  /**
+   * Analyze a given public API definition to ensure it exposes only types available in itself and
+   * in an allowed set of external APIs.
+   */
+  public Apilyzer(PublicApi publicApi, List<String> allows, boolean ignoreDeprecated,
+      Consumer<Problem> problemConsumer) {
+    this.problemReporter = new ProblemReporter(problemConsumer);
+    this.allowsPs = new PatternSet(allows);
+    this.ignoreDeprecated = ignoreDeprecated;
+    this.publicApi = publicApi;
+  }
+
+  private boolean allowedExternalApi(String fqName) {
+    // TODO make default allows configurable?
+    if (fqName.startsWith("java.")) {
+      return true;
+    }
+    return allowsPs.anyMatch(fqName);
+  }
+
+  private boolean deprecatedToIgnore(AnnotatedElement element) {
+    return ignoreDeprecated && element.isAnnotationPresent(Deprecated.class);
+  }
+
+  private boolean isOk(Class<?> clazz) {
+
+    while (clazz.isArray()) {
+      clazz = clazz.getComponentType();
+    }
+
+    if (clazz.isPrimitive()) {
+      return true;
+    }
+
+    String fqName = clazz.getName();
+    return publicApi.contains(fqName) || allowedExternalApi(fqName);
+  }
+
+  private boolean checkClass(Class<?> clazz, Set<Class<?>> innerChecked) {
+
+    boolean ok = true;
+
+    if (deprecatedToIgnore(clazz)) {
+      return true;
+    }
+
+    // TODO check generic type parameters
+
+    for (Field field : ClassUtils.getFields(clazz)) {
+
+      if (deprecatedToIgnore(field)) {
+        continue;
+      }
+
+      if (!field.getDeclaringClass().getName().equals(clazz.getName())
+          && isOk(field.getDeclaringClass())) {
+        continue;
+      }
+
+      if (!isOk(field.getType())) {
+        problemReporter.field(clazz, field);
+        ok = false;
+      }
+    }
+
+    Constructor<?>[] constructors = clazz.getConstructors();
+    for (Constructor<?> constructor : constructors) {
+
+      if (constructor.isSynthetic()) {
+        continue;
+      }
+
+      if (deprecatedToIgnore(constructor)) {
+        continue;
+      }
+
+      Class<?>[] params = constructor.getParameterTypes();
+      for (Class<?> param : params) {
+        if (!isOk(param)) {
+          problemReporter.constructorParameter(clazz, param);
+          ok = false;
+        }
+      }
+
+      Class<?>[] exceptions = constructor.getExceptionTypes();
+      for (Class<?> exception : exceptions) {
+        if (!isOk(exception)) {
+          problemReporter.constructorException(clazz, exception);
+          ok = false;
+        }
+      }
+    }
+
+    for (Method method : ClassUtils.getMethods(clazz)) {
+
+      if (method.isSynthetic() || method.isBridge()) {
+        continue;
+      }
+
+      if (deprecatedToIgnore(method)) {
+        continue;
+      }
+
+      if (!method.getDeclaringClass().getName().equals(clazz.getName())
+          && isOk(method.getDeclaringClass())) {
+        continue;
+      }
+
+      if (!isOk(method.getReturnType())) {
+        problemReporter.methodReturn(clazz, method);
+        ok = false;
+      }
+
+      Class<?>[] params = method.getParameterTypes();
+      for (Class<?> param : params) {
+        if (!isOk(param)) {
+          problemReporter.methodParameter(clazz, method, param);
+          ok = false;
+        }
+      }
+
+      Class<?>[] exceptions = method.getExceptionTypes();
+      for (Class<?> exception : exceptions) {
+        if (!isOk(exception)) {
+          problemReporter.methodException(clazz, method, exception);
+          ok = false;
+        }
+      }
+    }
+
+    for (Class<?> class1 : ClassUtils.getInnerClasses(clazz)) {
+
+      if (innerChecked.contains(class1)) {
+        continue;
+      }
+
+      innerChecked.add(class1);
+
+      if (deprecatedToIgnore(class1)) {
+        continue;
+      }
+
+      if (publicApi.excludes(class1)) {
+        // this inner class is explicitly excluded from API so do not check it
+        continue;
+      }
+
+      if (!isOk(class1) && !checkClass(class1, innerChecked)) {
+        problemReporter.innerClass(clazz, class1);
+        ok = false;
+      }
+    }
+
+    return ok;
+  }
+
+  public void check() {
+    publicApi.classStream().forEach(c -> checkClass(c, new HashSet<Class<?>>()));
+  }
+
+}

src/main/java/net/revelc/code/apilyzer/maven/plugin/PatternSet.java → src/main/java/net/revelc/code/apilyzer/PatternSet.java

@@ -12,38 +12,29 @@
  * limitations under the License.
  */
 
-package net.revelc.code.apilyzer.maven.plugin;
+package net.revelc.code.apilyzer;
 
-import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.regex.Pattern;
+import java.util.stream.Collectors;
 
+/**
+ * A set of patterns to match classes on the class path.
+ */
 class PatternSet {
   private final List<Pattern> patterns;
 
   PatternSet(List<String> regexs) {
-    if (regexs.size() == 0) {
-      patterns = Collections.emptyList();
-    } else {
-      patterns = new ArrayList<>();
-      for (String regex : regexs) {
-        patterns.add(Pattern.compile(regex));
-      }
-    }
+    patterns = regexs.isEmpty() ? Collections.emptyList()
+        : regexs.stream().map(Pattern::compile).collect(Collectors.toList());
   }
 
-  boolean matchesAny(String input) {
-    for (Pattern pattern : patterns) {
-      if (pattern.matcher(input).matches()) {
-        return true;
-      }
-    }
-
-    return false;
+  boolean anyMatch(String input) {
+    return patterns.stream().anyMatch(p -> p.matcher(input).matches());
   }
 
-  public int size() {
-    return patterns.size();
+  boolean isEmpty() {
+    return patterns.isEmpty();
   }
 }