如何用java过滤器修改响应体？

Question

我想对 HTTP 响应（采用 json 格式）执行一些过滤器逻辑。

我已成功更改响应正文，但是当正文的（字符串）大小更改时：我丢失了最后一个字符。

为了简化起见，我创建了一个简单的 Spring Boot 应用程序，我的 rest 控制器只有 Web 依赖项。

我的休息控制器

@RestController
@RequestMapping("/home/")
public class RestControllerHome {

@GetMapping (produces=MediaType.APPLICATION_JSON_VALUE)
public String home() {
        return "{ \"name\" : \"Peter\" }";
  }
}

我的过滤器

@Component
public class MyFilter implements Filter {

@Override
public void destroy() { }

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

    HtmlResponseWrapper capturingResponseWrapper = new HtmlResponseWrapper((HttpServletResponse) response);
    filterChain.doFilter(request, capturingResponseWrapper);        
    if (response.getContentType() != null && response.getContentType().contains("application/json")) {
        String content = capturingResponseWrapper.getCaptureAsString();

        // This code works fine
        //response.getWriter().write(content.toUpperCase());

        // This code doesn't works because the content size is changed
        response.getWriter().write("{ \"name\" : \"************r\" }");

    }
}

@Override
public void init(FilterConfig arg0) throws ServletException {  }    
}

HttpServletResponseWrapper // 在写入之前捕获响应

public class HtmlResponseWrapper extends HttpServletResponseWrapper {

private final ByteArrayOutputStream capture;
private ServletOutputStream output;
private PrintWriter writer;

public HtmlResponseWrapper(HttpServletResponse response) {
    super(response);
    capture = new ByteArrayOutputStream(response.getBufferSize());
}

@Override
public ServletOutputStream getOutputStream() {
    if (writer != null) {
        throw new IllegalStateException("getWriter() has already been called on this response.");
    }

    if (output == null) {
        // inner class - lets the wrapper manipulate the response 
        output = new ServletOutputStream() {
            @Override
            public void write(int b) throws IOException {
                capture.write(b);
            }

            @Override
            public void flush() throws IOException {
                capture.flush();
            }

            @Override
            public void close() throws IOException {
                capture.close();
            }

            @Override
            public boolean isReady() {
                return false;
            }

            @Override
            public void setWriteListener(WriteListener arg0) {
            }
        };
    }

    return output;
}

@Override
public PrintWriter getWriter() throws IOException {
    if (output != null) {
        throw new IllegalStateException("getOutputStream() has already been called on this response.");
    }

    if (writer == null) {
        writer = new PrintWriter(new OutputStreamWriter(capture,
                getCharacterEncoding()));
    }

    return writer;
}

@Override
public void flushBuffer() throws IOException {
    super.flushBuffer();

    if (writer != null) {
        writer.flush();
    } else if (output != null) {
        output.flush();
    }
}

public byte[] getCaptureAsBytes() throws IOException {
    if (writer != null) {
        writer.close();
    } else if (output != null) {
        output.close();
    }

    return capture.toByteArray();
}

public String getCaptureAsString() throws IOException {
    return new String(getCaptureAsBytes(), getCharacterEncoding());
}

}

在我的doFilter方法中，以下代码...

// This code works fine
response.getWriter().write(content.toUpperCase());

// This code doesn't works because the content size is changed
//response.getWriter().write("{ \"name\" : \"************r\" }");

...给我以下输出： {"NAME": "PETER"} 这告诉我，代码工作正常。

但是，实际上我想更改正文内容...

// This code works fine
//response.getWriter().write(content.toUpperCase());

// This code doesn't works because the content size is changed
response.getWriter().write("{ \"name\" : \"************r\" }");

...和之前的代码，给了我一个不完整的文本正文作为输出：**{ "name" : "**********

我究竟做错了什么？我的应用程序有一个更大的 json 主体，过滤器中有更复杂的逻辑。但是，如果我不让它工作，我就无法使我的其余代码工作。请帮忙。

我从https://www.leveluplunch.com/java/tutorials/034-modify-html-response-using-filter/ 获取了 Filter 和 HttpServletResponseWrapper

Answer 1

多亏了JBNizet的帮助，我发现解决办法是添加Content Lenght：

String newContent = "{ \"name\" : \"************r\" }";
response.setContentLength(newContent .length());
response.getWriter().write(newContent);