运用Filter，ThreadLocal和Reflection，实现form到bean的填充

开发者在线 Builder.com.cn 更新时间:2008-02-28作者：Nurhachi Jang 来源:CSDN

做过web开发的人可能都有这种感觉，不时的需要从request中提取参数及数据，如果有一种方式可以省却这一步骤，是否会令你的开发工作更愉悦呢？本文在此做了如下的探讨。

很显然，从request中提取参数需要一个尽职尽责的，但是又很优雅的让我们感觉不到它的辛苦工作的模块来实现，它的任务就是，1）截取所有的 request，2）从request取出数据并填充到bean留给其他人使用。大概你也会想到Filter，它的特性符合要求。

Filter截取了请求如何处理呢？ 我想到了2种方式（当然，还有其它的），

1）request参数需要指明本次提交的数据要填充至哪个bean，且参数与bean的field严格匹配，这样利用 Reflection ，取出bean的field，然后从request.getParameter(field)取得数据进行填充。
2）采取配置文件进行request 的form数据到bean的映射，方式也是采用Reflection来完成填充工作。

2种方式各有优缺点，方式1不够灵活，方式2则对于某些人看来则是烦琐，毕竟还需要配置，也失去了本文简化request form处理的目的。因此本人推荐第一种方式，即使存在某些情况，也可以在bean中增加新方法来处理。

数据的有效性检查也放在bean里做，将数据无效的信息放在bean的error hashmap里，在filter填充完bean后，检查bean是否有效，有无效的数据，则直接返回客户端；否则，调用chain.doFilter (request, response)继续处理，并将这个bean放入ThreadLocal中，留待后续class访问，当这个线程结束后，bean会被垃圾收集器清除。

Filter样例：

/*
 * SimpleFilter.java
 *
 * Created on 2006年9月20日, 下午2:54
 */

package org.openthoughts.testings;

import Java.io.*;
import Java.lang.reflect.Field;
import Java.lang.reflect.InvocationTargetException;
import Java.lang.reflect.Method;
import Java.util.HashMap;
import javax.servlet.*;
import javax.servlet.http.*;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import org.openthoughts.util.Form2BeanUtil;

/**
 * Stuff a bean specified by request with form data.
 *
 * @author <a href="[e-mail]">javafuns</a>
 * @version
 */

public class SimpleFilter implements Filter {
   
    // The filter configuration object we are associated with.  If
    // this value is null, this filter instance is not currently
    // configured.
    private FilterConfig filterConfig = null;
   
    public SimpleFilter() {
    }
   
    /**
     * Init method for this filter
     *
     */
    public void init(FilterConfig filterConfig) {
        this.filterConfig = filterConfig;
    }
 /**
     * Do actual work for filling.
     *
     * @param request The servlet request we are processing
     * @param result The servlet response we are creating
     * @param chain The filter chain we are processing
     *
     * @exception IOException if an input/output error occurs
     * @exception ServletException if a servlet error occurs
     */
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain)
            throws IOException, ServletException {
        String beanName = ((HttpServletRequest)request).getParameter("formbean");
System.err.println(" form bean is " + beanName);
        Class beanClazz = null;
        Object beanObject = null;
        boolean isValid = false;
       
        if(beanName != null) {
            try {
                beanClazz = Class.forName(beanName);
                if(beanClazz != null) {
                    beanObject = beanClazz.newInstance();
                }
            } catch (ClassNotFoundException ex) {
                request.setAttribute("MainErrMsg", beanName + " not found");
                this.filterConfig.getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
                return;
            } catch (InstantiationException ex) {
                request.setAttribute("MainErrMsg", beanName + " can not be instantiated");
                this.filterConfig.getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
                return;
            } catch (IllegalAccessException ex) {
                request.setAttribute("MainErrMsg", beanName + " not access");
                this.filterConfig.getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
                return;
            }
        }
               
        if(beanObject != null) {
            Field[] fields = beanClazz.getDeclaredFields();

            for(Field field : fields) {
                Method beanMethod = null;
                String fieldName = field.getName();
                String fieldValue = ((HttpServletRequest)request).getParameter(fieldName);
                StringBuilder sb = new StringBuilder();
                sb.append("set");
                sb.append(fieldName.substring(0, 1).toUpperCase());
                sb.append(fieldName.substring(1));
               
                try {
                    beanMethod = beanClazz.getDeclaredMethod(sb.toString(), String.class);
                } catch (SecurityException ex) {
                    request.setAttribute("MainErrMsg", " Security reason ");
                    this.filterConfig.getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
                    return;
                } catch (NoSuchMethodException ex) {
                    request.setAttribute("MainErrMsg", beanName + " does not have method named " + sb.toString());
                    this.filterConfig.getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
                    return;
                }

if(beanMethod != null) {
                    try {
                        beanMethod.invoke(beanObject, fieldValue);
                    } catch (IllegalArgumentException ex) {
                        request.setAttribute("MainErrMsg", "illegal argument for the method " + sb.toString() + " of " + beanName);
                        this.filterConfig.getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
                        return;
                    } catch (InvocationTargetException ex) {
                        request.setAttribute("MainErrMsg", beanName + " invoke target exception ");
                        this.filterConfig.getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
                        return;
                    } catch (IllegalAccessException ex) {
                        request.setAttribute("MainErrMsg", beanName + " illegal access to " + sb.toString());
                        this.filterConfig.getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
                        return;
                    }
                }
            }
            Form2BeanUtil.put(beanObject);
           
            Method getAllErrors = null;
            try {
                getAllErrors = beanClazz.getDeclaredMethod("getAllErrors");
            } catch (SecurityException ex) {
                System.err.println("Security exception when call getAllErrors()");
            } catch (NoSuchMethodException ex) {
                System.err.println("No such method named getAllErrors()");
            }
           
            if(getAllErrors != null) {
                try {
                    isValid = ((HashMap)getAllErrors.invoke(beanObject)).isEmpty();
                } catch (IllegalArgumentException ex) {
                    System.err.println("Illegal argument for getAllErrors()");
                } catch (IllegalAccessException ex) {
                    System.err.println("Illegal Access to getAllErrors()");
                } catch (InvocationTargetException ex) {
                    System.err.println("Invocation target exception");
                }
            }
        }
       
        if(beanName == null || isValid) {
            chain.doFilter(request, response);
        } else {
            if(beanObject != null) {
                request.setAttribute("formbean", beanObject);
            }
            this.filterConfig.getServletContext().getRequestDispatcher(getRequestURI(request)).forward(request, response);
        }
    }

    /**
     * Destroy method for this filter
     *
     */
    public void destroy() {
    }

    public String getRequestURI(ServletRequest request) {
        String requestURI = ((HttpServletRequest)request).getRequestURI();
        String queryString = ((HttpServletRequest)request).getQueryString();
        return requestURI + queryString;
    }
   
    /**
     * Return a String representation of this object.
     */
    public String toString() {
       
        if (filterConfig == null) return ("SimpleFilter()");
        StringBuffer sb = new StringBuffer("SimpleFilter(");
        sb.append(filterConfig);
        sb.append(")");
        return (sb.toString());
    }

}

Bean样例：

/*
 * SimpleBean.java
 *
 * Created on 2006年9月20日, 下午5:51
 */

package org.openthoughts.beans;

import Java.io.Serializable;
import Java.util.HashMap;

/**
 * @author Administrator
 */
public class SimpleBean implements Serializable {
   
    private String userName;
   
    private String password;
   
    public SimpleBean() {
       
    }
   
    public String getUserName() {
        return userName;
    }
   
    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getPassword() {
        return password;
    }
   
    public void setPassword(String password) {
        this.password = password;
    }
   
    //错误信息
    public HashMap getAllErrors() {
        return new HashMap();
    }
}



ThreadLocal实现：

/*
 * Form2BeanUtil.java
 *
 * Created on 2006年9月20日, 下午4:51
 *
 * To change this template, choose Tools | Template Manager
 * and open the template in the editor.
 */

package org.openthoughts.util;

/**
 * Hold formbean for appropriate thread via ThreadLocal.
 *
 * @author <a href="[e-mail]">javafuns</a>
 */
public class Form2BeanUtil {
   
    private static final ThreadLocal container = new ThreadLocal();
   
    /**
     * Put the form bean to ThreadLocal.
     */
    public static void put(Object object) {
        container.set(object);
    }
   
    /**
     * Get the current thread's form bean.
     */
    public static Object get() {
        return container.get();
    }
}


PS: 类似的方式在很多框架都有实现，比如struts的formbean