import java.util.Enumeration;
import java.util.Map;
import java.util.Vector;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
/**
* 思路：
* 第一步：声明一个成员变量是Map。用于设置我们修改后的表单参数
* 第二部：重写request里面的获得表单参数的四个方法。设置值都是通过我们修改后参数的变量Map来获得值
* @author ranger
*
*/
public class NullValueHandlerRequestWrapper extends HttpServletRequestWrapper {
public NullValueHandlerRequestWrapper(HttpServletRequest request) {
super(request);
}
private Map<String, String[]> parameterMap;
public void setParameterMap(Map<String, String[]> parameterMap) {
this.parameterMap = parameterMap;
}
@Override
public String getParameter(String name) {
String[] results = parameterMap.get(name);
return results[0];
}
@Override
public Map<String, String[]> getParameterMap() {
return this.parameterMap;
}
@Override
public Enumeration<String> getParameterNames() {
Vector<String> vector = new Vector<String>(parameterMap.keySet());
return vector.elements();
}
@Override
public String[] getParameterValues(String name) {
return parameterMap.get(name);
}
}
//修改请求表单参数。
//问题：HTTPServletRequest对象并没有提供修改请求表单参数的方法。如何解决呢？
//答：Servlet技术里面提供了一个Wrapper来解决表单参数设置的。Warpper实现了重新包装一个对象设置在过滤链里面
import java.io.IOException;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
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 javax.servlet.http.HttpServletRequest;
public class NullvalueHandlerFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
//获得所有字段
Map<String, String[]> parameterMap = new HashMap<>(request.getParameterMap());
Set<Entry<String, String[]>> entrySet = parameterMap.entrySet();
Iterator<Entry<String, String[]>> iterator = entrySet.iterator();
while (iterator.hasNext()) {
Entry<String, String[]> entry = iterator.next();
if (entry.getValue()!=null) {
for(int i=0;i<entry.getValue().length;i++) {
if ("".equals(entry.getValue()[i])) {
iterator.remove();
}
}
}
}
//parameterMap就会将空字符串转成null.
//注意：request对象是无法修改表单数据的！！ServletRequest对象是容Tomcat产生的，我们有没有办法new创建.
NullValueHandlerRequestWrapper wrapper =new NullValueHandlerRequestWrapper((HttpServletRequest)request);
wrapper.setParameterMap(parameterMap);
//获得重写后的请求
chain.doFilter(wrapper, response);
}
@Override
public void destroy() {
}
}
在web.xml中加入
<filter> <filter-name>nullvalueHandlerFilter</filter-name> <filter-class>org.chu.filter.NullvalueHandlerFilter</filter-class> </filter> <filter-mapping> <filter-name>nullvalueHandlerFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>
