setcharacterencodingfilter.java

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package com.res.webprint.sample;

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.UnavailableException;


/**
 * <p>Title: WebPrint System</p>
 * <p>Description: </p>
 * <p>Copyright: Copyright (c) 2005</p>
 * <p>Company: Realesoft Technology Inc.</p>
 * @author not attributable
 * @version 1.0
 * Example filter that sets the character encoding to be used in parsing the
 * incoming request, either unconditionally or only if the client did not
 * specify a character encoding.
 * 如果原来没有设置request的编码，就设置；否则保持不变
 */

public class SetCharacterEncodingFilter implements Filter {

  protected String encoding = null;
  protected FilterConfig filterConfig = null;
  protected boolean ignore = true;


/**
 * Take this filter out of service.
 */

public void destroy() {
  this.encoding = null;
  this.filterConfig = null;
}


/**
 * Select and set (if specified) the character encoding to be used to
 * interpret request parameters for this request.
 */

public void doFilter(ServletRequest request, ServletResponse response,FilterChain chain)throws IOException, ServletException {

// Conditionally select and set the character encoding to be used

if (ignore || (request.getCharacterEncoding() == null)) {

    String encoding = selectEncoding(request);

    if (encoding != null)
      request.setCharacterEncoding(encoding);//设置request编码的地方
}

// Pass control on to the next filter
// 传递控制到下一个过滤器

chain.doFilter(request, response);

}


/**
 * Place this filter into service.
 * 从web-app的web.xml文件中读取初始参数的值
 */

public void init(FilterConfig filterConfig) throws ServletException {

  this.filterConfig = filterConfig;
  this.encoding = filterConfig.getInitParameter("encoding");
  String value = filterConfig.getInitParameter("ignore");

  if (value == null)
    this.ignore = true;
  else if (value.equalsIgnoreCase("true"))
    this.ignore = true;
  else if (value.equalsIgnoreCase("yes"))
    this.ignore = true;
  else
    this.ignore = false;

}


/**
 * Select an appropriate character encoding to be used, based on the
 * characteristics of the current request and/or filter initialization
 * parameters. If no character encoding should be set, return
 * <code>null</code>.
 * 选择request原来的编码
 */

protected String selectEncoding(ServletRequest request) {
  return (this.encoding);
}

}