JSP 中文亂碼徹底解決：兩大經典方案（工具方法 vs Filter 過濾器）

亂碼根因

瀏覽器發送請求參數預設以 ISO-8859-1 編碼；伺服器若以 GBK/UTF-8 解碼即產生亂碼。解決核心：統一雙端編碼或正確轉碼。

方案一：工具類轉碼法（適用舊專案快速修補）

在 JSP 頁面或共用檔定義靜態方法：

<%!
    public static String toChinese(String str) {
        if (str == null) return null;
        try {
            byte[] bytes = str.getBytes("ISO-8859-1");
            return new String(bytes, "GBK"); // 或 UTF-8
        } catch (Exception e) { return str; }
    }
%>

<%-- 使用 --%>
String name = toChinese(request.getParameter("name"));

缺點：每個取參數處皆需呼叫、易遺漏、POST/GET 需分開處理、效能稍差。

方案二：Filter 統一編碼（推薦、一勞永逸）

實作 javax.servlet.Filter，在 doFilter 早期設定請求編碼，並包裝 HttpServletRequest 覆寫 getParameter* 方法自動轉碼。

完整 Filter 實作

package filters;

import java.io.IOException;
import javax.servlet.*;

public class EncodingFilter implements Filter {
    private String encoding = "UTF-8";
    private boolean ignore = true;

    public void init(FilterConfig config) {
        String e = config.getInitParameter("encoding");
        if (e != null) encoding = e;
        String ig = config.getInitParameter("ignore");
        if (ig != null) ignore = Boolean.parseBoolean(ig);
    }

    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
            throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) req;
        // POST 請求直接設定編碼
        if ("POST".equalsIgnoreCase(request.getMethod())) {
            if (ignore || request.getCharacterEncoding() == null) {
                request.setCharacterEncoding(encoding);
            }
        } else {
            // GET 請求需包裝 Request 覆寫 getParameter
            request = new RequestWrapper(request, encoding);
        }
        chain.doFilter(request, res);
    }

    public void destroy() {}
}

// 包裝類
class RequestWrapper extends HttpServletRequestWrapper {
    private String encoding;
    public RequestWrapper(HttpServletRequest request, String encoding) {
        super(request); this.encoding = encoding;
    }
    private String decode(String s) {
        try { return new String(s.getBytes("ISO-8859-1"), encoding); }
        catch (Exception e) { return s; }
    }
    @Override public String getParameter(String name) { return decode(super.getParameter(name)); }
    @Override public String[] getParameterValues(String name) {
        String[] vals = super.getParameterValues(name);
        if (vals != null) for (int i=0;i

<filter>
    <filter-name>EncodingFilter</filter-name>
    <filter-class>filters.EncodingFilter</filter-class>
    <init-param><param-name>encoding</param-name><param-value>UTF-8</param-value></init-param>
    <init-param><param-name>ignore</param-name><param-value>true</param-value></init-param>
</filter>
<filter-mapping>
    <filter-name>EncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

<Connector port="8080" protocol="HTTP/1.1"
           URIEncoding="UTF-8" useBodyEncodingForURI="true" />