在servlet的doGet（）里面调用方法一直报空指针异常

总共就一个超链接连了一个servlet
servlet里的代码是：
package com.simple.mvc;

import java.io.IOException;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/getAllProject")
public class GetAllProjectServlet extends HttpServlet {
private static final long serialVersionUID = 2L;

protected void doGet(HttpServletRequest request,
        HttpServletResponse response) throws ServletException, IOException {
    DAO dao=new DAO();
    List<Project> prs=dao.getAllProject();
    System.out.println(prs.size());
}

}
DAO里面的代码是：
package com.simple.mvc;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

import org.junit.Test;

public class DAO {

@Test
public void test(){
    DAO dao=new DAO();
    List<Project> prs=dao.getAllProject();
    System.out.println(prs.size());
}

public List<Project> getAllProject(){
    List<Project> prs=new ArrayList<>();
    Connection connection =null;
    PreparedStatement preparedStatement=null;
    ResultSet resultSet=null;
    try {
        connection=JDBCTools.getConnection();
        String sql="SELECT p_id,p_name,t_name "+
                    "FROM project p,teacher t "+
                    "WHERE p.`t_id`=t.`t_id` AND p_if=2";
        preparedStatement = connection.prepareStatement(sql);
        resultSet = preparedStatement.executeQuery();
        while(resultSet.next()){
            int p_id=resultSet.getInt(1);
            String p_name=resultSet.getString(2);
            String t_name=resultSet.getString(3);
            Project project = new Project(p_id, p_name,t_name);
            prs.add(project);
        }
    } catch (Exception e) {
        e.printStackTrace();
    }finally{
        JDBCTools.release(resultSet, preparedStatement, connection);
    }
    return prs;
}

}
在超链接访问servlet时就报java.lang.NullPointerException
我看了是因为List prs=dao.getAllProject();返回为null
但是为什么会返回为null
我在DAO写了一个测试单元，测试返回不为null呀，求大神解答
报错内容为
java.lang.NullPointerException
at java.util.Properties$LineReader.readLine(Properties.java:434)
at java.util.Properties.load0(Properties.java:353)
at java.util.Properties.load(Properties.java:341)
at com.simple.mvc.JDBCTools.getConnection(JDBCTools.java:44)
at com.simple.mvc.DAO.getAllProject(DAO.java:28)
at com.simple.mvc.GetAllProjectServlet.doGet(GetAllProjectServlet.java:22)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:962)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:445)0

at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1115)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)

把DAO注解为Bean，比如@service，或者@Mapper，然后在doGet() 的类里用@AutoWired或者@Resource注入。

List prs=new ArrayList<>();这段代码代表，List prs=dao.getAllProject();返回不会空指针，建议还是查查dao是不是
new出问题了，dao是null,所以空指针了

请贴出完整的报错信息
看描述，正常执行到servlet内你测试通过的方法，看不出问题

at com.simple.mvc.JDBCTools.getConnection(JDBCTools.java:44)看错误应该是JDBCTools类里面的问题

你是用的什么框架啊？

应该是注解有没用对的地方。

我感觉 应该是 你这个方法读取配置文件时出现的问题 JDBCTools.getConnection(JDBCTools.java:44)
java.lang.NullPointerException
at java.util.Properties$LineReader.readLine(Properties.java:434)

数据库建立连接报的错

1、怎么没有import Dao的包，正常的没导入会报错，但是你代码确实没见导入
2、把doPost( )的空方法也补上，以前碰到过，没有doPost( )方法，会影响doGet( )方法的调用

我也是调用数据库里的数据转入arraylist里，如何转成json格式放doget()里，一直报空指针异常，里面明明有数据，不知道为什么