java利用过滤器实现编码的转换,内容输出的替换

在页面建个表单

 <form action="login.do" method="post">
        <input type="text" name="username" />
        <input type="submit" value="确定" />
    </form>

建个servlet

web.xml

  <servlet>
    <servlet-name>LoginServlert</servlet-name>
    <servlet-class>servlet.LoginServlert</servlet-class>
  </servlet>
 
  <servlet-mapping>
    <servlet-name>LoginServlert</servlet-name>
    <url-pattern>/login.do</url-pattern>
  </servlet-mapping>

package servlet;
 
import java.io.IOException;
import java.io.PrintWriter;
 
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
public class LoginServlert extends HttpServlet {
    public LoginServlert() {
        super();
    }
    public void destroy() {
        super.destroy();
    }
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String username = request.getParameter("username");
        System.out.println("获取的username:>>>>>>"+username);
    }
    public void init() throws ServletException {
    }
}

后台情况是这样的:

乱码了.

可以通过过滤器来解决

新建一个过滤器EncodingFilter.java

package filter;
 
import java.io.IOException;
 
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 EncodingFilter implements Filter{
    private String encoding = "";
    private String filterName = "";
 
    public void init(FilterConfig filterConfig) throws ServletException {
        encoding = filterConfig.getInitParameter("encoding");
        filterName = filterConfig.getFilterName();
        if (encoding == null || "".equals(encoding)) {
            encoding = "UTF-8";
        }
        System.out.println("获得编码值......");
 
    }
 
    public void doFilter(ServletRequest request, ServletResponse res,
            FilterChain chain) throws IOException, ServletException {
        HttpServletRequest req=(HttpServletRequest)request;
        System.out.println("请求被" + filterName + "过滤了.......");
        // 分别对请求和响应进行编码设置
        request.setCharacterEncoding(encoding);
        res.setCharacterEncoding(encoding);
        chain.doFilter(req, res);
        System.out.println("响应被被" + filterName + "过滤了.......");
    }
 
    public void destroy() {
        System.out.println("请求被销毁......");
    }
}

在web.xml中配置filter

   <filter>
      <filter-name>EncodingFilter</filter-name>
      <filter-class>filter.EncodingFilter</filter-class>
      <init-param>
          <param-name>encoding</param-name>
          <param-value>utf-8</param-value>
      </init-param>
  </filter>
  <filter-mapping>
      <filter-name>EncodingFilter</filter-name>
      <url-pattern>*.do</url-pattern>
  </filter-mapping> 

跑起来:

正常了.

我们换在地址栏里输入汉字,看看是否乱码.

结果是这样的

过滤器不起作用了,怎么办.

其实request.setCharacterEncoding(encoding);只对消息体中的数据起作用,对url中的参数不起作用了.

对上面的过滤器进行优化.

编写RequestEncodingWrapper.java

package filter;
 
import java.io.UnsupportedEncodingException;
 
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
 
public class RequestEncodingWrapper extends HttpServletRequestWrapper {
    private String encoding = "";
 
    public RequestEncodingWrapper(HttpServletRequest request) {
        // 必须调用父类构造方法
        super(request);
    }
    public RequestEncodingWrapper(HttpServletRequest request,String encoding){
        // 必须调用父类构造方法
        super(request);
        this.encoding=encoding;
    }
 
    @Override
    public String getParameter(String name) {
        String value=getRequest().getParameter(name);
        try {
            //将参数值进行编码转换
            if(value!=null&&!"".equals(value)){
                value=new String(value.trim().getBytes("iso-8859-1"),encoding);
            }
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        return value;
    }
 
}

优化EncodingFilter.java后

package filter;
 
import java.io.IOException;
 
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 EncodingFilter implements Filter {
    private String encoding = "";
    private String filterName = "";
 
    public void init(FilterConfig filterConfig) throws ServletException {
        encoding = filterConfig.getInitParameter("encoding");
        filterName = filterConfig.getFilterName();
        if (encoding == null || "".equals(encoding)) {
            encoding = "UTF-8";
        }
        System.out.println("获得编码值......");
 
    }
 
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        HttpServletRequest req=(HttpServletRequest)request;
        System.out.println("请求被" + filterName + "过滤了.......");
        if("GET".equals(req.getMethod())){
            req=new RequestEncodingWrapper(req,encoding);
        }else {
            request.setCharacterEncoding(encoding);
        }
        // 分别对请求和响应进行编码设置
        response.setCharacterEncoding(encoding);
        chain.doFilter(req, response);
        System.out.println("响应被被" + filterName + "过滤了.......");
    }
 
    public void destroy() {
        System.out.println("请求被销毁......");
    }
 
}

好了.

Filter接口有三个方法:

init(FilterConfig filterConfig) 初始化过滤器,filterConfig参数可以得到过滤器初始化的配置参数信息.

doFilter(ServletRequest request, ServletResponse res,FilterChain chain)

request表示客户端的请求,rewponse表示对应请求的响应,chain是过滤器对象,.在该方法中的特定过滤器完成后,

可调用doFilter请求传给过滤器中的下一个过滤器,也可以直接返回响应内容,还可以将目标重定向.

destroy():释放过滤器中使用的资源.

参数FilterConfig filterConfig有四个方法:

public String getFilterName()　　　　得到过滤器的名字

public String getInitParameter(String name)　　　　得到过滤器中初始化的参数值.

publi Enumeration getInitParameterNames()　　　　得到过滤器配置中的所有初始化参数名字的枚举类型.

publi ServletContext getServlet()　　　　得到Servlet上下文对象.

说完了请求,我们再来说说响应.

我们经常需要在向浏览器输出内容时,过滤一些敏感词汇.

新建一个内容替换的封装器ResponseReplaeWrapper.java

package filter;
 
import java.io.CharArrayWriter;
import java.io.IOException;
import java.io.PrintWriter;
 
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;
 
public class ResponseReplaeWrapper extends HttpServletResponseWrapper {
    private CharArrayWriter charWriter = new CharArrayWriter();
    public ResponseReplaeWrapper(HttpServletResponse response){
        //必须调用父类构造方法
        super(response);
    }
    public PrintWriter getWriter() throws IOException{
        //返回字符数组Writer,缓存内容
        return new PrintWriter(charWriter);
    }
    public CharArrayWriter getCharWriter(){
        return charWriter;
    }
 
}

过滤器:

package filter;
 
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Properties;
 
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.HttpServletResponse;
 
public class ReplaceFilter implements Filter {
    private Properties propert = new Properties();
 
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("ReplaceFilter  init.....");
 
        // 通过filterConfig获得初始胡文件名
        String filePath = filterConfig.getInitParameter("filePath");
        try {
            // 导入资源文件
            propert.load(ReplaceFilter.class.getClassLoader()
                    .getResourceAsStream(filePath));
 
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
 
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        HttpServletResponse res = (HttpServletResponse) response;
        // 实例化响应器包装类
        ResponseReplaeWrapper resp = new ResponseReplaeWrapper(res);
        chain.doFilter(request, resp);
        // 缓存输出字符
        String outString = resp.getCharWriter().toString();
        // 循环替换不合法的字符
        for (Object o : propert.keySet()) {
            String key = (String) o;
            outString = outString.replace(key, propert.getProperty(key));
        }
        // 利用原先的HttpServletResponse输出字符
        PrintWriter out = res.getWriter();
        out.write(outString);
    }
 
    public void destroy() {
        System.out.println("ReplaceFilter destroy......");
    }
 
}

在web.xml中配置过滤器

<filter>
      <filter-name>ReplaceFilter</filter-name>
      <filter-class>filter.ReplaceFilter</filter-class>
      <init-param>
          <param-name>filePath</param-name>
          <param-value>/replace_ZH.properties</param-value>
      </init-param>
  </filter>
  <filter-mapping>
      <filter-name>ReplaceFilter</filter-name>
      <url-pattern>*.do</url-pattern>
  </filter-mapping> 

在src下新建配置文件replace_ZH.properties

建个测试的servlet

package servlet;
 
import java.io.IOException;
import java.io.PrintWriter;
 
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
public class ResponseServlet extends HttpServlet {
    public ResponseServlet() {
        super();
    }
 
    public void destroy() {
        super.destroy(); // Just puts "destroy" string in log
        // Put your code here
    }
 
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
 
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
        out.println("<HTML>");
        out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");
        out.println("  <BODY>");
        out.println("思思博士<br/>色情<br/>赌博<br/>dfdffddf");
        /*out.print("    This is ");
        out.print(this.getClass());
        out.println(", using the GET method");*/
        out.println("  </BODY>");
        out.println("</HTML>");
        out.flush();
        out.close();
    }
 
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
 
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
        out.println("<HTML>");
        out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");
        out.println("  <BODY>");
        out.print("    This is ");
        out.print(this.getClass());
        out.println(", using the POST method");
        out.println("  </BODY>");
        out.println("</HTML>");
        out.flush();
        out.close();
    }
 
    public void init() throws ServletException {
    }
 
}