Java中常见HTTP 400错误的原因和正确处理方法

400 Bad Request: Missing required parameter 'userId'

// 确保所有必需参数都已包含
Map<String, String> params = new HashMap<>();
params.put("userId", "12345"); // 必须包含

400 Bad Request: Invalid format for parameter 'date', expected format 'yyyy-MM-dd'

// 格式化日期参数
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
String formattedDate = sdf.format(new Date());

400 Bad Request: Content-Type header is missing

HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestProperty("Content-Type", "application/json");

HTTP 400 - 错误请求（请求标头过长）

// 对于Tomcat服务器，在application.yml中配置
server:
  tomcat:
    max-http-header-size: 16384 # 设置请求头最大大小为16KB

400 Bad Request: Invalid JSON format in request body

// 使用Jackson正确序列化对象
ObjectMapper objectMapper = new ObjectMapper();
String json = objectMapper.writeValueAsString(user);

400 Bad Request: Character encoding error in request body

// 在发送请求时指定编码
out = new PrintWriter(new OutputStreamWriter(conn.getOutputStream(), "UTF-8"));

feign.FeignException: status 400 reading

@Component
public class TomcatFactoryCustomizer implements WebServerFactoryCustomizer<TomcatServletWebServerFactory> {
    @Override
    public void customize(TomcatServletWebServerFactory factory) {
        factory.addConnectorCustomizers(connector -> {
            if (connector.getProtocolHandler() instanceof AbstractHttp11Protocol) {
                ((AbstractHttp11Protocol<?>) connector.getProtocolHandler()).setMaxHttpHeaderCount(200);
            }
        });
    }
}

400 Bad Request: Header size exceeds maximum allowed (8KB)

# application.yml
server:
  tomcat:
    max-http-header-size: 16384 # 设置请求头最大大小为16KB

400 Bad Request: Invalid URL format

// 使用URLEncoder正确编码URL
String encodedName = URLEncoder.encode("John Doe", StandardCharsets.UTF_8.name());
String url = "http://example.com/api?name=" + encodedName;

400 Bad Request: Method not allowed for this resource

// 确保使用正确的HTTP方法
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET"); // 应为GET，而不是POST

400 Bad Request: Request body too large

# application.yml
spring:
  http:
    max-request-size: 10MB # 设置请求体最大大小为10MB

java.io.IOException: Server returned HTTP response code: 400 for URL: ...

import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;

public class HttpErrorExample {
    public static void main(String[] args) {
        try {
            URL url = new URL("http://example.com/api");
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("POST");
            conn.setDoOutput(true);
            
            // 发送请求
            
            int responseCode = conn.getResponseCode();
            String responseMessage = conn.getResponseMessage();
            
            if (responseCode >= 400) {
                // 从错误流中读取响应体
                InputStream errorStream = conn.getErrorStream();
                String errorBody = convertStreamToString(errorStream);
                System.out.println("Error response: " + errorBody);
            } else {
                // 正常响应
                InputStream inputStream = conn.getInputStream();
                String responseBody = convertStreamToString(inputStream);
                System.out.println("Response: " + responseBody);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    
    private static String convertStreamToString(InputStream is) {
        BufferedReader reader = new BufferedReader(new InputStreamReader(is));
        StringBuilder sb = new StringBuilder();
        String line;
        try {
            while ((line = reader.readLine()) != null) {
                sb.append(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                is.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return sb.toString();
    }
}

@ControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(HttpClientErrorException.class)
    public ResponseEntity<String> handleHttpClientErrorException(HttpClientErrorException ex) {
        return ResponseEntity.status(ex.getStatusCode()).body("Error: " + ex.getMessage());
    }
}