Java-Error：已经为此响应调用了getWriter（）

Question

我正在尝试添加一个tomcat过滤器，但是在执行时，我收到的错误消息是已经为此响应调用了getWriter（）。

有问题的代码：

包过滤器;

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.*;

public final class ExampleFilter implements Filter {

[...]

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);
    }
}

[..]

如何防止此错误？