如何将HttpServletResponse的Body提取为字符串？

由于你的场景是将HttpServletResponse作为数据容器而非实际发送HTTP响应，无法使用过滤器捕获内容，最直接的方案是通过自定义HttpServletResponseWrapper替换输出流，缓存所有写入的内容，最终转换为字符串。

实现步骤 #

1. 编写响应包装类，将输出流替换为ByteArrayOutputStream以缓存内容

import javax.servlet.ServletOutputStream;
import javax.servlet.WriteListener;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.StringWriter;

public class CapturingResponseWrapper extends HttpServletResponseWrapper {
    private final ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
    private PrintWriter writer;

    public CapturingResponseWrapper(HttpServletResponse response) {
        super(response);
    }

    @Override
    public ServletOutputStream getOutputStream() throws IOException {
        return new ServletOutputStream() {
            @Override
            public boolean isReady() {
                return true;
            }

            @Override
            public void setWriteListener(WriteListener writeListener) {}

            @Override
            public void write(int b) throws IOException {
                byteArrayOutputStream.write(b);
            }
        };
    }

    @Override
    public PrintWriter getWriter() throws IOException {
        if (writer == null) {
            writer = new PrintWriter(new StringWriter() {
                @Override
                public void write(String str, int off, int len) {
                    try {
                        byteArrayOutputStream.write(str.getBytes(getCharacterEncoding()), off, len);
                    } catch (IOException e) {
                        throw new RuntimeException(e);
                    }
                }
            });
        }
        return writer;
    }

    public String getCapturedBody() {
        if (writer != null) {
            writer.flush();
        }
        try {
            return byteArrayOutputStream.toString(getCharacterEncoding());
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

2. 在业务代码中使用包装类捕获Body

// 包装原始HttpServletResponse
CapturingResponseWrapper responseWrapper = new CapturingResponseWrapper(originalResponse);

// 执行原本写入响应的逻辑（比如业务代码中调用response.getWriter()/getOutputStream()写入内容）
responseWrapper.getWriter().write("示例响应内容");
responseWrapper.getWriter().flush();

// 提取Body字符串
String responseBody = responseWrapper.getCapturedBody();

注意事项 #

• 务必调用flush()确保所有写入内容被缓存到ByteArrayOutputStream中
• 使用getCharacterEncoding()保证字符串编码与原响应一致，避免乱码
• 该方案无需依赖过滤器，直接在代码中包装响应对象，完全适配你将Response作为数据容器的改造场景

内容的提问来源于stack exchange，提问作者Cube.