我正在运行一个简单的Web项目。在我的一个servlet中，我从表单中获取用户的参数，并运行UserDao类的getIf方法，该方法从数据库中返回匹配某种条件的所有用户。
这是getIf代码的代码：
@Override
public synchronized List<User> getIf(User user) {
List<User> users = new ArrayList<>();
users = getAll();
int num = users.size();
System.out.println(num);
for (int i = 0; i < num; i++) {
User potentialUser = users.get(i);
boolean result = true;
if (user.getUsername() != null && !user.getUsername().equals(potentialUser.getUsername())) {
result = false;
} else if (user.getPassword() != null && !user.getPassword().equals(potentialUser.getPassword())) {
result = false;
} else if (user.getFirstName() != null && !user.getFirstName().equals(potentialUser.getFirstName())) {
result = false;
} else if (user.getLastName() != null && !user.getLastName().equals(potentialUser.getLastName())) {
result = false;
} else if (user.getUserType() != null && !user.getUserType().equals(potentialUser.getUserType())) {
result = false;
} else if (user.getAge() != null && !user.getAge().equals(potentialUser.getAge())) {
result = false;
}
if (!result) {
users.remove(potentialUser);
}
}
return users;
}
每当我运行此servlet时，通过提交表单，都会收到此错误：
java.lang.IndexOutOfBoundsException: Index: 13, Size: 12
at java.util.ArrayList.rangeCheck(ArrayList.java:657)
at java.util.ArrayList.get(ArrayList.java:433)
at com.model.databasePackage.implementations.UserDao.getIf(UserDao.java:205)
at com.web.servlets.SearchServiceServlet.doPost(SearchServiceServlet.java:55)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:200)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:834)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1415)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)
处理请求的servlet的代码如下： 包com.web.servlets;
import com.model.databasePackage.implementations.UserDao;
import com.model.objects.User;
import com.model.objects.User_Type;
import java.io.IOException;
import java.util.List;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class SearchServiceServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public SearchServiceServlet() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
response.setContentType("txt/html");
UserDao dao = (UserDao) getServletContext().getAttribute("userDao");
//Reading parameters
String first_name = request.getParameter("first_name");
String last_name = request.getParameter("last_name");
Integer age = null;
try {
age = Integer.valueOf(request.getParameter("age"));
} catch (NumberFormatException ex) {
}
//if the parameters is empty string,then its variable is set to null.
first_name = first_name.equals("") ? null : first_name;
last_name = last_name.equals("") ? null : last_name;
User userEq = new User.UserBuilder(null, null, age, new User_Type("User"), first_name, last_name).build();
List<User> users = dao.getIf(userEq);
System.out.println(users.size());
response.sendRedirect("search.html");
}
}
我使用maven，tomcat 9和netbeans运行该项目。
答案 0 :(得分：4)
请勿修改您要迭代的内容。这是一个简单的解决方案，可以跟踪要删除的用户，并在迭代完成后将其删除。
@Override
public synchronized List<User> getIf(User user) {
List<User> users = new ArrayList<>();
users = getAll();
int num = users.size();
System.out.println(num);
List<User> toRemove = new ArrayList<>();
for (int i = 0; i < num; i++) {
User potentialUser = users.get(i);
boolean result = true;
if (user.getUsername() != null && !user.getUsername().equals(potentialUser.getUsername())) {
result = false;
} else if (user.getPassword() != null && !user.getPassword().equals(potentialUser.getPassword())) {
result = false;
} else if (user.getFirstName() != null && !user.getFirstName().equals(potentialUser.getFirstName())) {
result = false;
} else if (user.getLastName() != null && !user.getLastName().equals(potentialUser.getLastName())) {
result = false;
} else if (user.getUserType() != null && !user.getUserType().equals(potentialUser.getUserType())) {
result = false;
} else if (user.getAge() != null && !user.getAge().equals(potentialUser.getAge())) {
result = false;
}
if (!result) {
toRemove.add(user);
}
}
toRemove.forEach(u -> users.remove(u));
return users;
}
有一种更好的方法：
@Override
public synchronized List<User> getIf(User user) {
List<User> users = getAll();
return users.stream().filter(potentialUser -> {
boolean result = true;
if (user.getUsername() != null && !user.getUsername().equals(potentialUser.getUsername())) {
result = false;
} else if (user.getPassword() != null && !user.getPassword().equals(potentialUser.getPassword())) {
result = false;
} else if (user.getFirstName() != null && !user.getFirstName().equals(potentialUser.getFirstName())) {
result = false;
} else if (user.getLastName() != null && !user.getLastName().equals(potentialUser.getLastName())) {
result = false;
} else if (user.getUserType() != null && !user.getUserType().equals(potentialUser.getUserType())) {
result = false;
} else if (user.getAge() != null && !user.getAge().equals(potentialUser.getAge())) {
result = false;
}
return result;
}).collect(Collectors.toList());
}