前端修复，日志功能加入

src/main/java/com/mzh/library/controller/LoginServlet.java

@@ -8,6 +8,7 @@ import com.mzh.library.service.impl.AuthServiceImpl;
 import com.mzh.library.util.SessionAttributes;
 
 import java.io.IOException;
+import java.util.logging.Logger;
 
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
@@ -16,6 +17,7 @@ import javax.servlet.http.HttpServletResponse;
 import javax.servlet.http.HttpSession;
 
 public class LoginServlet extends HttpServlet {
+    private static final Logger LOGGER = Logger.getLogger(LoginServlet.class.getName());
     private static final String LOGIN_JSP = "/WEB-INF/jsp/auth/login.jsp";
     private static final String DASHBOARD_PATH = "/dashboard";
     private static final int SESSION_TIMEOUT_SECONDS = 30 * 60;
@@ -40,9 +42,13 @@ public class LoginServlet extends HttpServlet {
 
     @Override
     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
-        String username = trim(request.getParameter("username"));
+        String submittedUsername = request.getParameter("username");
+        String username = trim(submittedUsername);
         String password = request.getParameter("password");
-        String redirect = safeRedirect(request.getParameter("redirect"));
+        String submittedRedirect = request.getParameter("redirect");
+        String redirect = safeRedirect(submittedRedirect);
+
+        logLoginPost(request, submittedUsername, username, password, submittedRedirect, redirect);
 
         AuthenticationResult result = authService.authenticate(username, password);
         if (!result.isAuthenticated()) {
@@ -57,6 +63,26 @@ public class LoginServlet extends HttpServlet {
         response.sendRedirect(resolveRedirect(request, redirect));
     }
 
+    private void logLoginPost(
+        HttpServletRequest request,
+        String submittedUsername,
+        String username,
+        String password,
+        String submittedRedirect,
+        String redirect
+    ) {
+        LOGGER.info("Login POST reached"
+            + " remoteAddr=" + safeLogValue(request.getRemoteAddr())
+            + " contextPath=" + safeLogValue(request.getContextPath())
+            + " redirectSubmitted=" + !trim(submittedRedirect).isEmpty()
+            + " redirectAccepted=" + !redirect.isEmpty()
+            + " usernameSubmitted=" + (submittedUsername != null)
+            + " usernameLength=" + length(submittedUsername)
+            + " normalizedUsernameLength=" + username.length()
+            + " usernameNormalizedChanged=" + !username.equals(nullToEmpty(submittedUsername))
+            + " passwordSubmitted=" + (password != null));
+    }
+
     private boolean isAuthenticated(HttpServletRequest request) {
         HttpSession session = request.getSession(false);
         return session != null && session.getAttribute(SessionAttributes.AUTHENTICATED_USER) != null;
@@ -97,4 +123,29 @@ public class LoginServlet extends HttpServlet {
     private String trim(String value) {
         return value == null ? "" : value.trim();
     }
+
+    private int length(String value) {
+        return value == null ? 0 : value.length();
+    }
+
+    private String nullToEmpty(String value) {
+        return value == null ? "" : value;
+    }
+
+    private String safeLogValue(String value) {
+        if (value == null) {
+            return "";
+        }
+
+        StringBuilder builder = new StringBuilder();
+        int limit = Math.min(value.length(), 120);
+        for (int i = 0; i < limit; i++) {
+            char current = value.charAt(i);
+            builder.append(Character.isISOControl(current) ? '?' : current);
+        }
+        if (value.length() > limit) {
+            builder.append("...");
+        }
+        return builder.toString();
+    }
 }