使用HttpServletResponseWrapper加密接口返回值时如何解决中文乱码问题？

使用HttpServletResponseWrapper加密接口返回值及中文乱码解决方案

在开发对外API接口时，数据加密至关重要。本文探讨在Filter中使用HttpServletResponseWrapper加密接口返回值时，如何有效避免中文乱码问题。 核心问题在于如何正确获取响应数据并进行加密处理。

以下代码片段展示了常见的错误尝试：使用CharArrayWriter缓存响应内容，并在flushBuffer方法中进行加密。然而，flushBuffer可能不会被执行，导致加密失败。 尝试在FilterChain.doFilter之后获取数据，则可能出现中文乱码。

HttpServletResponse response = (HttpServletResponse) servletResponse;
EncryptResponseWrapper encryptResponseWrapper = new EncryptResponseWrapper(response);
encryptResponseWrapper.setCharacterEncoding("UTF-8");
filterChain.doFilter(servletRequest, encryptResponseWrapper);

关键在于EncryptResponseWrapper的实现。改进后的代码如下：

package com.wondersgroup.wdls.js.wapper;

import com.wondersgroup.wdls.js.web.utils.DESUtils;

import javax.servlet.*;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;
import java.io.*;

public class EncryptResponseWrapper extends HttpServletResponseWrapper {
    private CharArrayWriter charArrayWriter = null;
    private PrintWriter writer = null;
    private ServletOutputStream out = null;

    public EncryptResponseWrapper(HttpServletResponse response) throws IOException {
        super(response);
        charArrayWriter = new CharArrayWriter();
        out = new WrapperOutputStream(charArrayWriter);
        // 关键修改：显式指定UTF-8编码
        writer = new PrintWriter(new OutputStreamWriter(new WrapperOutputStream(charArrayWriter), "UTF-8"));
    }

    @Override
    public PrintWriter getWriter() throws IOException {
        return writer;
    }

    @Override
    public ServletOutputStream getOutputStream() throws IOException {
        return out;
    }

    public CharArrayWriter getCharArrayWriter() {
        return charArrayWriter;
    }

    @Override
    public void flushBuffer() throws IOException {
        if (out != null) {
            out.flush();
        }
        if (writer != null) {
            writer.flush();
        }
    }

    @Override
    public void reset() {
        charArrayWriter.reset();
    }

    public String getResponseData() throws IOException {
        flushBuffer();
        return charArrayWriter.toString();
    }

    private class WrapperOutputStream extends ServletOutputStream {
        private CharArrayWriter charArrayWriter = null;

        public WrapperOutputStream(CharArrayWriter charArrayWriter) {
            this.charArrayWriter = charArrayWriter;
        }

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

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

        @Override
        public void setWriteListener(WriteListener listener) {

        }
    }
}

解决中文乱码的关键在于: 在创建PrintWriter时，通过new OutputStreamWriter(..., "UTF-8")显式指定UTF-8编码。这确保了写入CharArrayWriter的数据使用正确的编码，避免了后续读取时出现乱码，从而保证了加密操作的正确性和数据的完整性。

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