问HttpServletResponseWrapper.toString()在过滤器中不返回任何内容

EN

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;

public class LogFilter implements Filter  {
    public void  init(FilterConfig config) 
            throws ServletException{

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


        System.out.println("BEFORE filter");

        ServletOutputStream out = response.getOutputStream();

        CharResponseWrapper responseWrapper = new CharResponseWrapper((HttpServletResponse) response);

        chain.doFilter(request, responseWrapper);

        System.out.println("status : "+responseWrapper.getStatus());
        String servletResponse = new String(responseWrapper.toString());

        out.write((servletResponse + " filtered all data without any issues <B>Hahaha :)</B>").getBytes()); // Here you can change the response


        System.out.println("AFTER filter, original response: "
                + servletResponse.toString());


    }
    public void destroy() {
    }
}

import java.io.CharArrayWriter;
import java.io.PrintWriter;

import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;

public class CharResponseWrapper extends HttpServletResponseWrapper {
    private CharArrayWriter output;

    public String toString() {
        return output.toString();
    }

    public CharResponseWrapper(HttpServletResponse response) {
        super(response);
        output = new CharArrayWriter();
    }

    public PrintWriter getWriter() {
        return new PrintWriter(output);
    }
}

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    <filter>
        <filter-name>LogFilter</filter-name>
        <filter-class>com.<<hidden>>.web.LogFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>LogFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
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