Java 激发'RequestDispatcher'时出现NullPointerException
我正在使用Java 激发'RequestDispatcher'时出现NullPointerException,java,rest,servlets,retrofit,requestdispatcher,Java,Rest,Servlets,Retrofit,Requestdispatcher,我正在使用改装连接到我的REST API。请检查下面的代码 import com.google.gson.Gson; import com.google.gson.GsonBuilder; import java.io.IOException; import java.io.PrintWriter; import java.util.Date; import java.util.List; import java.util.logging.L
改装
连接到我的REST API。请检查下面的代码
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;
/**
*
* @author The Ace
*/
public class SignUpLoaderServlet extends HttpServlet {
/**
* Processes requests for both HTTP <code>GET</code> and <code>POST</code>
* methods.
*
* @param request servlet request
* @param response servlet response
* @throws ServletException if a servlet-specific error occurs
* @throws IOException if an I/O error occurs
*/
protected void processRequest(final HttpServletRequest request, final HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
System.out.println("RUNNING!!!!!!!!!!!");
try {
GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.registerTypeAdapter(Date.class, new DateTypeDeserializer());
Gson gson = gsonBuilder.create();
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(BaseURLs.MESSAGING_URL)
.addConverterFactory(GsonConverterFactory.create(gson))
.build();
RestEndPointsInterface endPoint = retrofit.create(RestEndPointsInterface.class);
Call<List<ProfesionalBodyList>> call = endPoint.getAllProfesionalBodyLists();
call.enqueue(new Callback<List<ProfesionalBodyList>>() {
@Override
public void onResponse(Call<List<ProfesionalBodyList>> call, Response<List<ProfesionalBodyList>> rspn)
{
try {
List<ProfesionalBodyList> body = rspn.body();
for(int i=0;i<body.size();i++)
{
System.out.println(body.get(i).getProfessionalBody());
}
RequestDispatcher requestDispatcher = request.getRequestDispatcher("/create-account.jsp");
requestDispatcher.forward(request, response);
} catch (Exception ex) {
ex.printStackTrace();
}
}
@Override
public void onFailure(Call<List<ProfesionalBodyList>> call, Throwable ex) {
ex.printStackTrace();
}
});
} finally {
}
}
// <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
/**
* Handles the HTTP <code>GET</code> method.
*
* @param request servlet request
* @param response servlet response
* @throws ServletException if a servlet-specific error occurs
* @throws IOException if an I/O error occurs
*/
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
/**
* Handles the HTTP <code>POST</code> method.
*
* @param request servlet request
* @param response servlet response
* @throws ServletException if a servlet-specific error occurs
* @throws IOException if an I/O error occurs
*/
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
}
此代码引发以下异常
java.lang.NullPointerException
at com.tekhinno.xxx.signup.SignUpLoaderServlet$1.onResponse(SignUpLoaderServlet.java:80)
at retrofit2.OkHttpCall$1.callSuccess(OkHttpCall.java:132)
at retrofit2.OkHttpCall$1.onResponse(OkHttpCall.java:111)
at okhttp3.RealCall$AsyncCall.execute(RealCall.java:135)
at okhttp3.internal.NamedRunnable.run(NamedRunnable.java:32)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
但是,如果我将下面的代码行替换到finally()
块中,问题就消失了
RequestDispatcher requestDispatcher = request.getRequestDispatcher("/create-account.jsp");
requestDispatcher.forward(request, response);
我不知道为什么它在onResponse()
中不起作用。在那里运行很重要,因为我在转发操作发生之前从RESTAPI加载项
有什么想法吗?问题主要是因为调用是
异步的
,并且requestDispatcher
对象已经执行。然后,答案是等待,直到REST调用完成其工作负载。也就是说,同步执行Synchronous
改造也可以以同步方式进行。下面是代码
protected void processRequest(final HttpServletRequest request, final HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
System.out.println("RUNNING!!!!!!!!!!!");
try {
GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.registerTypeAdapter(Date.class, new DateTypeDeserializer());
Gson gson = gsonBuilder.create();
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(BaseURLs.MESSAGING_URL)
.addConverterFactory(GsonConverterFactory.create(gson))
.build();
RestEndPointsInterface endPoint = retrofit.create(RestEndPointsInterface.class);
Call<List<ProfesionalBodyList>> call = endPoint.getAllProfesionalBodyLists();
body = call.execute().body();
for (int i = 0; i < body.size(); i++) {
System.out.println(body.get(i).getProfessionalBody());
}
} finally {
RequestDispatcher requestDispatcher = request.getRequestDispatcher("/create-account.jsp");
request.setAttribute("ProfesionalBodyList", body);
requestDispatcher.forward(request, response);
}
}
受保护的void processRequest(最终HttpServletRequest请求,最终HttpServletResponse响应)
抛出ServletException、IOException{
setContentType(“text/html;charset=UTF-8”);
PrintWriter out=response.getWriter();
System.out.println(“RUNNING!!!!!!!!!!!”;
试一试{
GsonBuilder GsonBuilder=新的GsonBuilder();
gsonBuilder.registerTypeAdapter(Date.class,新的DateTypeDeserializer());
Gson-Gson=gsonBuilder.create();
改装改装=新改装.Builder()
.baseUrl(baseUrl.MESSAGING\u URL)
.addConverterFactory(GsonConverterFactory.create(gson))
.build();
RestEndPointsInterface端点=改型.create(RestEndPointsInterface.class);
Call Call=endPoint.getAllProfessionalBodyList();
body=call.execute().body();
对于(int i=0;i
Simpy注意它所说的
call.execute().body()的位置代码>。这是同步调用。您使用的是异步API,它在后台线程中发送请求,然后在响应可用时调用您,并且不会阻止请求处理线程。因此,在执行onResponse回调时,请求已经得到处理。@JBNizet:谢谢。那么,我该如何处理这种情况呢?