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MVEL is a powerful expression language for Java-based applications. It provides a plethora of features and is suited for everything from the smallest property binding and extraction, to full blown scripts.
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/**
 * MVEL 2.0
 * Copyright (C) 2007 The Codehaus
 * Mike Brock, Dhanji Prasanna, John Graham, Mark Proctor
 *
 * 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
 *
 *     http://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 org.mvel2.util;

import org.mvel2.ParserContext;
import org.mvel2.compiler.PropertyVerifier;

import java.lang.reflect.Field;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.util.Collection;
import java.util.Map;

import static java.lang.String.valueOf;
import static java.lang.reflect.Modifier.PUBLIC;
import static java.lang.reflect.Modifier.STATIC;
import static java.lang.reflect.Modifier.isPublic;
import static org.mvel2.DataConversion.canConvert;
import static org.mvel2.util.ParseTools.boxPrimitive;

public class PropertyTools {
  public static boolean isEmpty(Object o) {
    if (o != null) {
      if (o instanceof Object[]) {
        return ((Object[]) o).length == 0 ||
            (((Object[]) o).length == 1 && isEmpty(((Object[]) o)[0]));
      }
      else {
        return ("".equals(valueOf(o)))
            || "null".equals(valueOf(o))
            || (o instanceof Collection && ((Collection) o).size() == 0)
            || (o instanceof Map && ((Map) o).size() == 0);
      }
    }
    return true;
  }

  public static Method getSetter(Class clazz, String property) {
    property = ReflectionUtil.getSetter(property);

    for (Method meth : clazz.getMethods()) {
      if ((meth.getModifiers() & PUBLIC) != 0 && meth.getParameterTypes().length == 1
          && property.equals(meth.getName())) {
        return meth;
      }
    }

    return null;
  }

  public static Method getSetter(Class clazz, String property, Class type) {
    String simple = "set" + property;
    property = ReflectionUtil.getSetter(property);

    for (Method meth : clazz.getMethods()) {
      if ((meth.getModifiers() & PUBLIC) != 0 && meth.getParameterTypes().length == 1 &&
          (property.equals(meth.getName()) || simple.equals(meth.getName()))
          && (type == null || canConvert(meth.getParameterTypes()[0], type))) {
        return meth;
      }
    }

    return null;
  }

  public static boolean hasGetter(Field field) {
    Method meth = getGetter(field.getDeclaringClass(), field.getName());
    return meth != null && field.getType().isAssignableFrom(meth.getReturnType());
  }

  public static boolean hasSetter(Field field) {
    Method meth = getSetter(field.getDeclaringClass(), field.getName());
    return meth != null && meth.getParameterTypes().length == 1 &&
        field.getType().isAssignableFrom(meth.getParameterTypes()[0]);
  }

  public static Method getGetter(Class clazz, String property) {
    String simple = "get" + property;
    String simpleIsGet = "is" + property;
    String isGet = ReflectionUtil.getIsGetter(property);
    String getter = ReflectionUtil.getGetter(property);

    Method candidate = null;
    for (Method meth : clazz.getMethods()) {
      if ((meth.getModifiers() & PUBLIC) != 0 && (meth.getModifiers() & STATIC) == 0 && meth.getParameterTypes().length == 0
          && (getter.equals(meth.getName()) || property.equals(meth.getName()) || ((isGet.equals(meth.getName()) || simpleIsGet.equals(meth.getName())) && meth.getReturnType() == boolean.class)
          || simple.equals(meth.getName()))) {
        if (candidate == null || candidate.getReturnType().isAssignableFrom(meth.getReturnType())) {
          candidate = meth;
        }
      }
    }
    return candidate;
  }

  public static Class getReturnType(Class clazz, String property, ParserContext ctx) {
    return new PropertyVerifier(property, ctx, clazz).analyze();
  }

  public static Member getFieldOrAccessor(Class clazz, String property) {
    for (Field f : clazz.getFields()) {
      if (property.equals(f.getName())) {
        if ((f.getModifiers() & PUBLIC) != 0) return f;
        break;
      }
    }
    return getGetter(clazz, property);
  }

  public static Member getFieldOrWriteAccessor(Class clazz, String property) {
    Field field;
    try {
      if ((field = clazz.getField(property)) != null &&
          isPublic(field.getModifiers())) {
        return field;
      }
    }
    catch (NullPointerException e) {
      return null;
    }
    catch (NoSuchFieldException e) {
      // do nothing.
    }

    return getSetter(clazz, property);
  }

  public static Member getFieldOrWriteAccessor(Class clazz, String property, Class type) {
    for (Field f : clazz.getFields()) {
      if (property.equals(f.getName()) && (type == null || canConvert(f.getType(), type))) {
        return f;
      }
    }

    return getSetter(clazz, property, type);
  }

  public static boolean contains(Object toCompare, Object testValue) {
    if (toCompare == null)
      return false;
    else if (toCompare instanceof String)
      return ((String) toCompare).contains(valueOf(testValue));
      //    return ((String) toCompare).indexOf(valueOf(testValue)) > -1;
    else if (toCompare instanceof Collection)
      return ((Collection) toCompare).contains(testValue);
    else if (toCompare instanceof Map)
      return ((Map) toCompare).containsKey(testValue);
    else if (toCompare.getClass().isArray()) {
      for (Object o : ((Object[]) toCompare)) {
        if (testValue == null && o == null) return true;
        else if (o != null && o.equals(testValue)) return true;
      }
    }
    return false;
  }

  public static Object getPrimitiveInitialValue(Class type) {
    if (type == int.class) {
      return 0;
    }
    else if (type == boolean.class) {
      return false;
    }
    else if (type == char.class) {
      return (char) 0;
    }
    else if (type == double.class) {
      return 0d;
    }
    else if (type == long.class) {
      return 0l;
    }
    else if (type == float.class) {
      return 0f;
    }
    else if (type == short.class) {
      return (short) 0;
    }
    else if (type == byte.class) {
      return (byte) 0;
    }
    else {
      return 0;
    }
  }

  public static boolean isAssignable(Class to, Class from) {
    return (to.isPrimitive() ? boxPrimitive(to) : to).isAssignableFrom(from.isPrimitive() ? boxPrimitive(from) : from);
  }

  /**
   * Get the JVM version
   * @return first mvel.java.version, then java.version
   * @see System.getProperty("mvel.java.version");
   * @see System.getProperty("java.version");
   */
  public static String getJavaVersion() {
    return System.getProperty("mvel.java.version")!=null ?
            System.getProperty("mvel.java.version") :
            System.getProperty("java.version");
  }
}