SpringBoot ErrorPage 案例
案例描述
调用后端接口，发现接口返回的数据有两组 json, 非数组。非常奇怪🙉
{
"name": "John",
"age": 30
}
{
"path": "/examples/servlets/servlet/JsonExample",
"code": 500
}
SpringMVC 运行时异常
/**
* Servlet 包版本问题，导致 SpringMVC Servlet 打印日志报错
* @see org.springframework.web.servlet.FrameworkServlet#processRequest
*/
protected final void processRequest(HttpServletRequest request, HttpServletResponse response) {
try {
doService(request, response);
}
catch (ServletException | IOException ex) {
}
finally {
// HttpStatus httpStatus = HttpStatus.resolve(status); since 5.0 才有这个方法 ❌
logResult(request, response, failureCause, asyncManager);
publishRequestHandledEvent(request, response, startTime, failureCause);
}
}
问题分析
-
第一个 json 是业务逻辑返回内容。controller 逻辑没有发生异常，正常写入 response。
-
第二个 json 是 SpringMVC Servlet 发生异常后，由 Tomcat ErrorPage 转发到默认的错误处理 Servlet 生成的内容。
-
两个 json 内容通过 RequestDispatcher.include 方法，都写入到 response。
案例复现
借助 Tomcat examples 应用，可以快速搭建案例场景。✔
业务场景 Servlet
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;
import java.io.PrintWriter;
// Servlet 中返回 JSON 字符串
public class JsonServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("application/json");
response.setCharacterEncoding("UTF-8");
String json = "{\"name\": \"John\", \"age\": 30}";
PrintWriter out = response.getWriter();
out.print(json);
// 业务内容写入 response, response 变为 submit 状态。
out.flush();
// 模拟上述 SpringMVC 异常
if(true) {
throw new RuntimeException("Bad area ref ");
}
}
}
异常处理 Servlet
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;
import java.io.PrintWriter;
// 对应 SpringBoot 提供的 BasicErrorController
public class ErrorServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String path = request.getRequestURI();
String json = "{\"path\": \"" + path + "\", \"code\": 500}";
PrintWriter out = response.getWriter();
out.print(json);
}
}
errorPage 配置
<servlet>
<servlet-name>JsonExample</servlet-name>
<servlet-class>JsonServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>JsonExample</servlet-name>
<url-pattern>/servlets/servlet/JsonExample</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>ErrorExample</servlet-name>
<servlet-class>ErrorServlet</servlet-class>
</servlet>
<!-- 对应的注册过程： org.springframework.boot.autoconfigure.web.BasicErrorController -->
<servlet-mapping>
<servlet-name>ErrorExample</servlet-name>
<url-pattern>/error</url-pattern>
</servlet-mapping>
<!-- 对应： ErrorPageRegistry.addErrorPages(errorPage); -->
<error-page>
<exception-type>java.lang.RuntimeException</exception-type>
<location>/error</location>
</error-page>
编译运行
cd /d/services/apache-tomcat-8.0.48/webapps/examples/WEB-INF/classes
# /D/repository/javax/servlet/servlet-api/2.4/servlet-api-2.4.jar
javac -cp servlet-api-2.4.jar JsonServlet.java
javac -cp servlet-api-2.4.jar ErrorServlet.java
运行 Tomcat。 访问链接 http://localhost:8080/examples/servlets/servlet/JsonExample