"person.username.firstname"类型参数字符串自动组装成对象的原理

在使用Struts2、WebWork框架开发Web应用时，JSP页中的表单项，常常会使用这样的参数名：

<input type="text" name="person.username" />
<input type="password" name="person.password" />

 

甚至，可以有更多层次的，如：

<input type="text" name="person.username.firstname" />
<input type="text" name="person.username.lastname" />

 
上面第一例，在后端Java代码中，自然有一个Person类与之对应。其中，这个Person类包含2个属性:username, password，还有必要的Setter和Getter方法。
上面第二例，同样有一个Person类与之相对应，而Person类中包括了一个Username类型的属性"username"；而在Username类里，有firstname和lastname两个属性。同样，相应的Setter和Getter方法是必不可少的。
那么，那些框架是怎么自动将型如"person.username.firstname"的字符串，组装成相应的对象(如Person对象)的呢？
请看以下代码：

/*
 * Copyright (c) 2002-2003 by OpenSymphony
 * All rights reserved.
 */
package com.opensymphony.provider.bean;

import com.opensymphony.provider.BeanProvider;
import com.opensymphony.provider.ProviderConfigurationException;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.StringTokenizer;


/**
 * BeanProvider implementation for accessing properties.
 *
 * Can handle a.b.c.d -> getA().getB().getC().getD().
 * Access properties in this order: bean.getA(), bean.isA(), bean.a(), bean.a.
 *
 * Can also deal with setter methods.
 *
 * @author <a href="mailto:[e-mail]">Joe Walnes</a>
 * @version $Revision: 1.1.1.1 $
 */
public class DefaultBeanProvider implements BeanProvider {
    //~ Static fields/initializers /////////////////////////////////////////////

    private static String GET = "get";
    private static String SET = "set";
    private static String IS = "is";

    //~ Methods ////////////////////////////////////////////////////////////////

    public boolean setProperty(Object object, String property, Object value) {
        if ((property == null) || (object == null)) {
            return false;
        }

        // Split out property on dots ( "person.name.first" -> "person","name","first" -> getPerson().getName().getFirst() )
        StringTokenizer st = new StringTokenizer(property, ".");

        if (st.countTokens() == 0) {
            return false;
        }

        // Holder for Object at current depth along chain.
        Object current = object;

        try {
            // Loop through properties in chain.
            for (int i = 0; st.hasMoreTokens(); i++) {
                String currentPropertyName = st.nextToken();

                if (i < st.countTokens()) {
                    // This is a getter
                    current = invokeProperty(current, currentPropertyName);
                } else {
                    // Final property in chain, hence setter
                    try {
                        // Call setter
                        Class cls = current.getClass();
                        PropertyDescriptor pd = new PropertyDescriptor(currentPropertyName, current.getClass());
                        pd.getWriteMethod().invoke(current, new Object[] {value});

                        return true;
                    } catch (Exception e) {
                        return false;
                    }
                }
            }

            // Return holder Object
            return true;
        } catch (NullPointerException e) {
            // It is very likely that one of the properties returned null. If so, catch the exception and return null.
            return false;
        }
    }

    public Object getProperty(Object object, String property) {
        if ((property == null) || (object == null)) {
            return null;
        }

        // Split out property on dots ( "person.name.first" -> "person","name","first" -> getPerson().getName().getFirst() )
        StringTokenizer st = new StringTokenizer(property, ".");

        if (st.countTokens() == 0) {
            return null;
        }

        // Holder for Object at current depth along chain.
        Object result = object;

        try {
            // Loop through properties in chain.
            while (st.hasMoreTokens()) {
                String currentPropertyName = st.nextToken();

                // Assign to holder the next property in the chain.
                result = invokeProperty(result, currentPropertyName);
            }

            // Return holder Object
            return result;
        } catch (NullPointerException e) {
            // It is very likely that one of the properties returned null. If so, catch the exception and return null.
            return null;
        }
    }

    public void destroy() {
    }

    public void init() throws ProviderConfigurationException {
    }

    /**
     * Convert property name into getProperty name ( "something" -> "getSomething" )
     */
    private String createMethodName(String prefix, String propertyName) {
        return prefix + propertyName.toUpperCase().charAt(0) + propertyName.substring(1);
    }

    /**
     * Invoke the method/field getter on the Object.
     * It tries (in order) obj.getProperty(), obj.isProperty(), obj.property(), obj.property.
     */
    private Object invokeProperty(Object obj, String property) {
        if ((property == null) || (property.length() == 0)) {
            return null; // just in case something silly happens.
        }

        Class cls = obj.getClass();
        Object[] oParams = {};
        Class[] cParams = {};

        try {
            // First try object.getProperty()
            Method method = cls.getMethod(createMethodName(GET, property), cParams);

            return method.invoke(obj, oParams);
        } catch (Exception e1) {
            try {
                // First try object.isProperty()
                Method method = cls.getMethod(createMethodName(IS, property), cParams);

                return method.invoke(obj, oParams);
            } catch (Exception e2) {
                try {
                    // Now try object.property()
                    Method method = cls.getMethod(property, cParams);

                    return method.invoke(obj, oParams);
                } catch (Exception e3) {
                    try {
                        // Now try object.property()
                        Field field = cls.getField(property);

                        return field.get(obj);
                    } catch (Exception e4) {
                        // oh well
                        return null;
                    }
                }
            }
        }
    }
}

 

oscore-2.2.5中的类，代码不难，且有注释，我就不多解析了。如有疑问，请提出来，我尽力解决。

评论

2 楼 rongxh2010 2010-06-14  

heqishan 写道

   try {  
                         // Call setter  
                         Class cls = current.getClass();  
                         PropertyDescriptor pd = new PropertyDescriptor(currentPropertyName, current.getClass());  
                         pd.getWriteMethod().invoke(current, new Object[] {value});  
   
                         return true;  
                     } catch (Exception e) {  
                         return false;  
                     }  

这段不明白。。。

PropertyDescriptor 这个是什么？

Java的一个类，用来获取Getter和Setter方法很方便。具体，请看JDK的文档相关说明：http://java.sun.com/j2se/1.5.0/docs/api/java/beans/PropertyDescriptor.html

1 楼 heqishan 2010-06-09  

   try {  
                         // Call setter  
                         Class cls = current.getClass();  
                         PropertyDescriptor pd = new PropertyDescriptor(currentPropertyName, current.getClass());  
                         pd.getWriteMethod().invoke(current, new Object[] {value});  
   
                         return true;  
                     } catch (Exception e) {  
                         return false;  
                     }  

这段不明白。。。

PropertyDescriptor 这个是什么？