仅当ContentType === JSON时才更改Java过滤器中的ContentType或CharacterEncoding

Question

我正在尝试确保来自基于Jersey的Java应用程序的所有JSON响应均在其ContentType标头中附加了UTF-8字符编码参数。

所以，如果它是一个JSON响应，我想响应报头的Content-Type要

内容类型：application / json; charset = UTF-8

EDIT: I know I can do this on a case by case basis, but I'd like to do it globally, so it affects all content responses that have a content type of "application/json".

如果无论内容类型如何，我都尝试在过滤器中设置字符编码，则效果很好。但是我只想在ContentType为“ application /
json”时设置字符编码。我发现response.getContentType（）方法始终返回null，除非我先调用chain.doFilter。但是，如果我尝试在此之后更改字符编码，似乎总是会被覆盖。

import java.io.IOException;
import javax.servlet.*;
import html" target="_blank">javax.servlet.http.*;
import javax.ws.rs.core.MediaType;

public class EnsureJsonResponseIsUtf8Filter implements Filter
{
    private class SimpleWrapper extends HttpServletResponseWrapper
    {
        public SimpleWrapper(HttpServletResponse response)
        {
            super(response);
        }

        @Override
        public String getCharacterEncoding()
        {
            return "UTF-8";
        }
    }

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

        if (response.getContentType() != null && response.getContentType().contains(MediaType.APPLICATION_JSON))
        {
            response.setCharacterEncoding("UTF-8");
            chain.doFilter(request, new SimpleWrapper((HttpServletResponse) response));
        }
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException
    {
    }

    @Override
    public void destroy()
    {
    }
}

我见过其他类似的问题，但似乎没有一个问题。我尝试将我的过滤器注册为第一个也是最后一个没有运气的过滤器。

Answer 1

多亏了此页面上的其他答案，我找到了一种实现方法。。。非常接近他们的建议，但是事实证明，使它起作用的唯一方法是重写“
getOutputStream”并查看此时的contentType。我已将此过滤器作为链中的第一个过滤器，它似乎工作正常。

import java.io.IOException;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.ws.rs.core.MediaType;

public class EnsureJsonIsUtf8ResponseFilter implements Filter
{
    final String APPLICATION_JSON_WITH_UTF8_CHARSET = MediaType.APPLICATION_JSON + ";charset=" + java.nio.charset.StandardCharsets.UTF_8;

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException
    {
        HttpServletResponse r = (HttpServletResponse) response;
        HttpServletResponse wrappedResponse = new HttpServletResponseWrapper(r) 
        {
            @Override
            public ServletOutputStream getOutputStream() throws java.io.IOException
            {
                ServletResponse response = this.getResponse();

                String ct = (response != null) ? response.getContentType() : null;
                if (ct != null && ct.toLowerCase().startsWith(MediaType.APPLICATION_JSON))
                {
                    response.setContentType(APPLICATION_JSON_WITH_UTF8_CHARSET);
                }

                return super.getOutputStream();
            }
        };

        chain.doFilter(request, wrappedResponse); 
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException
    {
        // This method intentionally left blank
    }

    @Override
    public void destroy()
    {
        // This method intentionally left blank
    }
}