思考一个问题：如何将map里面的值，映射到一个对象里的属性，不通过手动方式设置！！！

很多人会说：BeanUtils的

public static void populate(Object bean, Map properties)
    throws IllegalAccessException, InvocationTargetException
  {
    BeanUtilsBean.getInstance().populate(bean, properties);
  }

这个方法，是的没错。

下面我们来分析一下他的源码：

package org.apache.commons.beanutils;

import java.beans.IndexedPropertyDescriptor;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Array;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import org.apache.commons.beanutils.expression.Resolver;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

public class BeanUtilsBean
{
  private static final ContextClassLoaderLocal BEANS_BY_CLASSLOADER = new ContextClassLoaderLocal()
  {
    protected Object initialValue() {
      return new BeanUtilsBean();
    }
  };

  private Log log = LogFactory.getLog(BeanUtils.class);
  private ConvertUtilsBean convertUtilsBean;
  private PropertyUtilsBean propertyUtilsBean;
  private static final Method INIT_CAUSE_METHOD = getInitCauseMethod();

  public static BeanUtilsBean getInstance()
  {
    return (BeanUtilsBean)BEANS_BY_CLASSLOADER.get();
  }

  public static void setInstance(BeanUtilsBean newInstance)
  {
    BEANS_BY_CLASSLOADER.set(newInstance);
  }

  public BeanUtilsBean()
  {
    this(new ConvertUtilsBean(), new PropertyUtilsBean());
  }

  public BeanUtilsBean(ConvertUtilsBean convertUtilsBean)
  {
    this(convertUtilsBean, new PropertyUtilsBean());
  }

  public BeanUtilsBean(ConvertUtilsBean convertUtilsBean, PropertyUtilsBean propertyUtilsBean)
  {
    this.convertUtilsBean = convertUtilsBean;
    this.propertyUtilsBean = propertyUtilsBean;
  }

  public Object cloneBean(Object bean)
    throws IllegalAccessException, InstantiationException, InvocationTargetException, NoSuchMethodException
  {
    if (log.isDebugEnabled()) {
      log.debug("Cloning bean: " + bean.getClass().getName());
    }
    Object newBean = null;
    if ((bean instanceof DynaBean))
      newBean = ((DynaBean)bean).getDynaClass().newInstance();
    else {
      newBean = bean.getClass().newInstance();
    }
    getPropertyUtils().copyProperties(newBean, bean);
    return newBean;
  }

  public void copyProperties(Object dest, Object orig)
    throws IllegalAccessException, InvocationTargetException
  {
    if (dest == null) {
      throw new IllegalArgumentException("No destination bean specified");
    }

    if (orig == null) {
      throw new IllegalArgumentException("No origin bean specified");
    }
    if (log.isDebugEnabled()) {
      log.debug("BeanUtils.copyProperties(" + dest + ", " + orig + ")");
    }

    if ((orig instanceof DynaBean)) {
      DynaProperty[] origDescriptors = ((DynaBean)orig).getDynaClass().getDynaProperties();

      for (int i = 0; i < origDescriptors.length; i++) {
        String name = origDescriptors[i].getName();

        if ((getPropertyUtils().isReadable(orig, name)) && (getPropertyUtils().isWriteable(dest, name)))
        {
          Object value = ((DynaBean)orig).get(name);
          copyProperty(dest, name, value);
        }
      }
    } else if ((orig instanceof Map)) {
      Iterator entries = ((Map)orig).entrySet().iterator();
      while (entries.hasNext()) {
        Map.Entry entry = (Map.Entry)entries.next();
        String name = (String)entry.getKey();
        if (getPropertyUtils().isWriteable(dest, name))
          copyProperty(dest, name, entry.getValue());
      }
    }
    else {
      PropertyDescriptor[] origDescriptors = getPropertyUtils().getPropertyDescriptors(orig);

      for (int i = 0; i < origDescriptors.length; i++) {
        String name = origDescriptors[i].getName();
        if (!"class".equals(name))
        {
          if ((getPropertyUtils().isReadable(orig, name)) && (getPropertyUtils().isWriteable(dest, name)))
            try
            {
              Object value = getPropertyUtils().getSimpleProperty(orig, name);

              copyProperty(dest, name, value);
            }
            catch (NoSuchMethodException e)
            {
            }
        }
      }
    }
  }

  public void copyProperty(Object bean, String name, Object value)
    throws IllegalAccessException, InvocationTargetException
  {
    if (log.isTraceEnabled()) {
      StringBuffer sb = new StringBuffer("  copyProperty(");
      sb.append(bean);
      sb.append(", ");
      sb.append(name);
      sb.append(", ");
      if (value == null) {
        sb.append("");
      } else if ((value instanceof String)) {
        sb.append((String)value);
      } else if ((value instanceof String[])) {
        String[] values = (String[])value;
        sb.append('[');
        for (int i = 0; i < values.length; i++) {
          if (i > 0) {
            sb.append(',');
          }
          sb.append(values[i]);
        }
        sb.append(']');
      } else {
        sb.append(value.toString());
      }
      sb.append(')');
      log.trace(sb.toString());
    }

    Object target = bean;
    Resolver resolver = getPropertyUtils().getResolver();
    while (resolver.hasNested(name)) {
      try {
        target = getPropertyUtils().getProperty(target, resolver.next(name));
        name = resolver.remove(name);
      } catch (NoSuchMethodException e) {
        return;
      }
    }
    if (log.isTraceEnabled()) {
      log.trace("    Target bean = " + target);
      log.trace("    Target name = " + name);
    }

    String propName = resolver.getProperty(name);
    Class type = null;
    int index = resolver.getIndex(name);
    String key = resolver.getKey(name);

    if ((target instanceof DynaBean)) {
      DynaClass dynaClass = ((DynaBean)target).getDynaClass();
      DynaProperty dynaProperty = dynaClass.getDynaProperty(propName);
      if (dynaProperty == null) {
        return;
      }
      type = dynaProperty.getType();
    } else {
      PropertyDescriptor descriptor = null;
      try {
        descriptor = getPropertyUtils().getPropertyDescriptor(target, name);

        if (descriptor == null)
          return;
      }
      catch (NoSuchMethodException e) {
        return;
      }
      type = descriptor.getPropertyType();
      if (type == null)
      {
        if (log.isTraceEnabled()) {
          log.trace("    target type for property '" + propName + "' is null, so skipping ths setter");
        }

        return;
      }
    }
    if (log.isTraceEnabled()) {
      log.trace("    target propName=" + propName + ", type=" + type + ", index=" + index + ", key=" + key);
    }

    if (index >= 0) {
      value = convert(value, type.getComponentType());
      try {
        getPropertyUtils().setIndexedProperty(target, propName, index, value);
      }
      catch (NoSuchMethodException e) {
        throw new InvocationTargetException(e, "Cannot set " + propName);
      }
    }
    else if (key != null)
    {
      try
      {
        getPropertyUtils().setMappedProperty(target, propName, key, value);
      }
      catch (NoSuchMethodException e) {
        throw new InvocationTargetException(e, "Cannot set " + propName);
      }
    }
    else {
      value = convert(value, type);
      try {
        getPropertyUtils().setSimpleProperty(target, propName, value);
      } catch (NoSuchMethodException e) {
        throw new InvocationTargetException(e, "Cannot set " + propName);
      }
    }
  }

  public Map describe(Object bean)
    throws IllegalAccessException, InvocationTargetException, NoSuchMethodException
  {
    if (bean == null)
    {
      return new HashMap();
    }

    if (log.isDebugEnabled()) {
      log.debug("Describing bean: " + bean.getClass().getName());
    }

    Map description = new HashMap();
    if ((bean instanceof DynaBean)) {
      DynaProperty[] descriptors = ((DynaBean)bean).getDynaClass().getDynaProperties();

      for (int i = 0; i < descriptors.length; i++) {
        String name = descriptors[i].getName();
        description.put(name, getProperty(bean, name));
      }
    } else {
      PropertyDescriptor[] descriptors = getPropertyUtils().getPropertyDescriptors(bean);

      Class clazz = bean.getClass();
      for (int i = 0; i < descriptors.length; i++) {
        String name = descriptors[i].getName();
        if (getPropertyUtils().getReadMethod(clazz, descriptors[i]) != null) {
          description.put(name, getProperty(bean, name));
        }
      }
    }
    return description;
  }

  public String[] getArrayProperty(Object bean, String name)
    throws IllegalAccessException, InvocationTargetException, NoSuchMethodException
  {
    Object value = getPropertyUtils().getProperty(bean, name);
    if (value == null)
      return null;
    if ((value instanceof Collection)) {
      ArrayList values = new ArrayList();
      Iterator items = ((Collection)value).iterator();
      while (items.hasNext()) {
        Object item = items.next();
        if (item == null) {
          values.add((String)null);
        }
        else {
          values.add(getConvertUtils().convert(item));
        }
      }
      return (String[])values.toArray(new String[values.size()]);
    }if (value.getClass().isArray()) {
      int n = Array.getLength(value);
      String[] results = new String[n];
      for (int i = 0; i < n; i++) {
        Object item = Array.get(value, i);
        if (item == null) {
          results[i] = null;
        }
        else {
          results[i] = getConvertUtils().convert(item);
        }
      }
      return results;
    }
    String[] results = new String[1];
    results[0] = getConvertUtils().convert(value);
    return results;
  }

  public String getIndexedProperty(Object bean, String name)
    throws IllegalAccessException, InvocationTargetException, NoSuchMethodException
  {
    Object value = getPropertyUtils().getIndexedProperty(bean, name);
    return getConvertUtils().convert(value);
  }

  public String getIndexedProperty(Object bean, String name, int index)
    throws IllegalAccessException, InvocationTargetException, NoSuchMethodException
  {
    Object value = getPropertyUtils().getIndexedProperty(bean, name, index);
    return getConvertUtils().convert(value);
  }

  public String getMappedProperty(Object bean, String name)
    throws IllegalAccessException, InvocationTargetException, NoSuchMethodException
  {
    Object value = getPropertyUtils().getMappedProperty(bean, name);
    return getConvertUtils().convert(value);
  }

  public String getMappedProperty(Object bean, String name, String key)
    throws IllegalAccessException, InvocationTargetException, NoSuchMethodException
  {
    Object value = getPropertyUtils().getMappedProperty(bean, name, key);
    return getConvertUtils().convert(value);
  }

  public String getNestedProperty(Object bean, String name)
    throws IllegalAccessException, InvocationTargetException, NoSuchMethodException
  {
    Object value = getPropertyUtils().getNestedProperty(bean, name);
    return getConvertUtils().convert(value);
  }

  public String getProperty(Object bean, String name)
    throws IllegalAccessException, InvocationTargetException, NoSuchMethodException
  {
    return getNestedProperty(bean, name);
  }

  public String getSimpleProperty(Object bean, String name)
    throws IllegalAccessException, InvocationTargetException, NoSuchMethodException
  {
    Object value = getPropertyUtils().getSimpleProperty(bean, name);
    return getConvertUtils().convert(value);
  }

public void populate(Object bean, Map properties)
    throws IllegalAccessException, InvocationTargetException
  {
    if ((bean == null) || (properties == null)) {
      return;
    }
    if (log.isDebugEnabled()) {
      log.debug("BeanUtils.populate(" + bean + ", " + properties + ")");
    }

    Iterator entries = properties.entrySet().iterator();
    while (entries.hasNext())
    {
      Map.Entry entry = (Map.Entry)entries.next();
      String name = (String)entry.getKey();
      if (name != null)
      {
        setProperty(bean, name, entry.getValue());
      }
    }
  }

  public void setProperty(Object bean, String name, Object value)
    throws IllegalAccessException, InvocationTargetException
  {
    if (log.isTraceEnabled()) {
      StringBuffer sb = new StringBuffer("  setProperty(");
      sb.append(bean);
      sb.append(", ");
      sb.append(name);
      sb.append(", ");
      if (value == null) {
        sb.append("");
      } else if ((value instanceof String)) {
        sb.append((String)value);
      } else if ((value instanceof String[])) {
        String[] values = (String[])value;
        sb.append('[');
        for (int i = 0; i < values.length; i++) {
          if (i > 0) {
            sb.append(',');
          }
          sb.append(values[i]);
        }
        sb.append(']');
      } else {
        sb.append(value.toString());
      }
      sb.append(')');
      log.trace(sb.toString());
    }

    Object target = bean;
    Resolver resolver = getPropertyUtils().getResolver();
    while (resolver.hasNested(name)) {
      try {
        target = getPropertyUtils().getProperty(target, resolver.next(name));
        name = resolver.remove(name);
      } catch (NoSuchMethodException e) {
        return;
      }
    }
    if (log.isTraceEnabled()) {
      log.trace("    Target bean = " + target);
      log.trace("    Target name = " + name);
    }

    String propName = resolver.getProperty(name);
    Class type = null;
    int index = resolver.getIndex(name);
    String key = resolver.getKey(name);

    if ((target instanceof DynaBean)) {
      DynaClass dynaClass = ((DynaBean)target).getDynaClass();
      DynaProperty dynaProperty = dynaClass.getDynaProperty(propName);
      if (dynaProperty == null) {
        return;
      }
      type = dynaProperty.getType();
    } else if ((target instanceof Map)) {
      type = Object.class;
    } else if ((target.getClass().isArray()) && (index >= 0)) {
      type = Array.get(target, index).getClass();
    } else {
      PropertyDescriptor descriptor = null;
      try {
        descriptor = getPropertyUtils().getPropertyDescriptor(target, name);

        if (descriptor == null)
          return;
      }
      catch (NoSuchMethodException e) {
        return;
      }
      if ((descriptor instanceof MappedPropertyDescriptor)) {
        if (((MappedPropertyDescriptor)descriptor).getMappedWriteMethod() == null) {
          if (log.isDebugEnabled()) {
            log.debug("Skipping read-only property");
          }
          return;
        }
        type = ((MappedPropertyDescriptor)descriptor).getMappedPropertyType();
      }
      else if ((index >= 0) && ((descriptor instanceof IndexedPropertyDescriptor))) {
        if (((IndexedPropertyDescriptor)descriptor).getIndexedWriteMethod() == null) {
          if (log.isDebugEnabled()) {
            log.debug("Skipping read-only property");
          }
          return;
        }
        type = ((IndexedPropertyDescriptor)descriptor).getIndexedPropertyType();
      }
      else if (key != null) {
        if (descriptor.getReadMethod() == null) {
          if (log.isDebugEnabled()) {
            log.debug("Skipping read-only property");
          }
          return;
        }
        type = value == null ? Object.class : value.getClass();
      } else {
        if (descriptor.getWriteMethod() == null) {
          if (log.isDebugEnabled()) {
            log.debug("Skipping read-only property");
          }
          return;
        }
        type = descriptor.getPropertyType();
      }

    }

    Object newValue = null;
    if ((type.isArray()) && (index < 0)) {
      if (value == null) {
        String[] values = new String[1];
        values[0] = null;
        newValue = getConvertUtils().convert(values, type);
      } else if ((value instanceof String)) {
        newValue = getConvertUtils().convert(value, type);
      } else if ((value instanceof String[])) {
        newValue = getConvertUtils().convert((String[])value, type);
      } else {
        newValue = convert(value, type);
      }
    } else if (type.isArray()) {
      if (((value instanceof String)) || (value == null)) {
        newValue = getConvertUtils().convert((String)value, type.getComponentType());
      }
      else if ((value instanceof String[])) {
        newValue = getConvertUtils().convert(((String[])(String[])value)[0], type.getComponentType());
      }
      else {
        newValue = convert(value, type.getComponentType());
      }
    }
    else if ((value instanceof String))
      newValue = getConvertUtils().convert((String)value, type);
    else if ((value instanceof String[])) {
      newValue = getConvertUtils().convert(((String[])(String[])value)[0], type);
    }
    else {
      newValue = convert(value, type);
    }

    try
    {
      getPropertyUtils().setProperty(target, name, newValue);
    } catch (NoSuchMethodException e) {
      throw new InvocationTargetException(e, "Cannot set " + propName);
    }
  }

  public ConvertUtilsBean getConvertUtils()
  {
    return convertUtilsBean;
  }

  public PropertyUtilsBean getPropertyUtils()
  {
    return propertyUtilsBean;
  }

  public boolean initCause(Throwable throwable, Throwable cause)
  {
    if ((INIT_CAUSE_METHOD != null) && (cause != null)) {
      try {
        INIT_CAUSE_METHOD.invoke(throwable, new Object[] { cause });
        return true;
      } catch (Throwable e) {
        return false;
      }
    }
    return false;
  }

  protected Object convert(Object value, Class type)
  {
    Converter converter = getConvertUtils().lookup(type);
    if (converter != null) {
      log.trace("        USING CONVERTER " + converter);
      return converter.convert(type, value);
    }
    return value;
  }

  private static Method getInitCauseMethod()
  {
    try
    {
      Class[] paramsClasses = { Throwable.class };
      return Throwable.class.getMethod("initCause", paramsClasses);
    } catch (NoSuchMethodException e) {
      Log log = LogFactory.getLog(BeanUtils.class);
      if (log.isWarnEnabled()) {
        log.warn("Throwable does not have initCause() method in JDK 1.3");
      }
      return null;
    } catch (Throwable e) {
      Log log = LogFactory.getLog(BeanUtils.class);
      if (log.isWarnEnabled())
        log.warn("Error getting the Throwable initCause() method", e);
    }
    return null;
  }
}