从EJB注入到servlet的NullPointerException
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Glassfish日志中报告的NullPointerException来自哪里？ ConverterServlet似乎有dollar作为BigInteger数字，非null。如果ConverterBean只记录美元金额，那将至少朝着正确的方向迈出一步。是不是正确地注入了EJB？
正确输出硬编码的美元金额：
金额是多少？ Servlet ConverterServlet at / ConverterApplication-war amount是999
美元：999类java.math.BigDecimal
但由于Glassfish报道的NPE，日元和欧元从未执行过：
[2017-04-17T00:12:27.609-0700] [glassfish 4.1] [WARNING] [] [javax.enterprise.web] [tid: _ThreadID=84 _ThreadName=http-listener-1(1)] [timeMillis: 1492413147609] [levelValue: 900] [[
StandardWrapperValve[ConverterServlet]: Servlet.service() for servlet ConverterServlet threw exception
java.lang.NullPointerException
at net.bounceme.dur.ejb.ConverterServlet.processRequest(ConverterServlet.java:41)
at net.bounceme.dur.ejb.ConverterServlet.doGet(ConverterServlet.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:687)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:416)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:283)
at com.sun.enterprise.v3.services.impl.ContainerMapper$HttpHandlerCallable.call(ContainerMapper.java:459)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:167)
at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:206)
at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:180)
at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:235)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:283)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:200)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:132)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:111)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:536)
at org.glassfish.grizzly.strategies.Abstractiostrategy.fireIOEvent(AbstractIOStrategy.java:112)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:117)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:56)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:137)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:591)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:571)
at java.lang.Thread.run(Thread.java:745)
]]
servlet的：
package net.bounceme.dur.ejb;
import java.io.IOException;
import java.io.PrintWriter;
import java.math.BigDecimal;
import javax.ejb.EJB;
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(urlPatterns = "/")
public class ConverterServlet extends HttpServlet {
@EJB
ConverterBean converter;
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
try (PrintWriter out = response.getWriter()) {
/* TODO output your page here. You may use following sample code. */
out.println("<!DOCTYPE html>");
out.println("<html>");
out.println("<head>");
out.println("<title>Servlet ConverterServlet</title>");
out.println("</head>");
out.println("<body>");
out.println("what is the amount?");
out.println("<h1>Servlet ConverterServlet at " + request.getContextPath() + "</h1>");
String stringAmount = "999";
out.println("amount is " + stringAmount);
out.println("<p>");
BigDecimal dollars = new BigDecimal(stringAmount);
out.println("dollars: " + dollars + " " + dollars.getClass());
out.println("<p>");
BigDecimal yen = converter.dollarToYen(dollars);
BigDecimal euros = converter.yenToEuro(yen);
out.println("never executed..");
out.println("yen");
out.println(yen);
out.println("<p>");
out.println("euros");
out.println(euros);
out.println("<p>");
out.println("</body>");
out.println("</html>");
}
}
// <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);
}
/**
* Returns a short description of the servlet.
*
* @return a String containing servlet description
*/
@Override
public String getServletInfo() {
return "Short description";
}// </editor-fold>
}
和EJB：
package net.bounceme.dur.ejb;
import java.math.BigDecimal;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import java.util.Properties;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.ejb.Stateless;
@Stateless
public class ConverterBean {
private static final Logger log = Logger.getLogger(ConverterBean.class.getName());
private static final Level LEVEL = Level.INFO;
private static final BigDecimal YEN_RATE = new BigDecimal("83.0602");
private static final BigDecimal EURO_RATE = new BigDecimal("0.0093016");
public BigDecimal dollarToYen(BigDecimal dollars) {
return YEN_RATE;
}
public BigDecimal yenToEuro(BigDecimal yen) {
return EURO_RATE;
}
public BigDecimal realdollarToYen(BigDecimal dollars) {
log.info("dollarToYen.." + dollars);
BigDecimal result = dollars.multiply(YEN_RATE);
return result.setScale(2, BigDecimal.ROUND_UP);
}
public BigDecimal realyenToEuro(BigDecimal yen) {
log.info("yenToEuro.." + yen);
BigDecimal result = yen.multiply(EURO_RATE);
return result.setScale(2, BigDecimal.ROUND_UP);
}
private void lookup() throws NamingException {
System.out.println("problem");
PropertiesReader pr = new PropertiesReader();
Properties webService = pr.getProps("WebService");
log.info(pr.toString());
log.info(new InitialContext().getEnvironment().toString());
}
}
应用树视图：
ConverterApplication/
├── build.xml
├── ConverterApplication-ejb
│ ├── build.xml
│ ├── nbproject
│ │ ├── ant-deploy.xml
│ │ ├── build-impl.xml
│ │ ├── genfiles.properties
│ │ ├── private
│ │ │ ├── private.properties
│ │ │ └── private.xml
│ │ ├── project.properties
│ │ └── project.xml
│ └── src
│ ├── conf
│ │ └── MANIFEST.MF
│ └── java
│ ├── net
│ │ └── bounceme
│ │ └── dur
│ │ └── ejb
│ │ ├── Client.java
│ │ ├── ConverterBean.java
│ │ └── PropertiesReader.java
│ └── resources
│ ├── JNDI.properties
│ └── WebService.properties
├── ConverterApplication-war
│ ├── build.xml
│ ├── nbproject
│ │ ├── ant-deploy.xml
│ │ ├── build-impl.xml
│ │ ├── genfiles.properties
│ │ ├── private
│ │ │ ├── private.properties
│ │ │ └── private.xml
│ │ ├── project.properties
│ │ └── project.xml
│ ├── src
│ │ ├── conf
│ │ │ └── MANIFEST.MF
│ │ └── java
│ │ └── net
│ │ └── bounceme
│ │ └── dur
│ │ └── ejb
│ │ ├── ConverterServlet.java
│ │ └── PropertiesReader.java
│ ├── test
│ └── web
│ ├── index.html
│ └── WEB-INF
│ └── web.xml
├── nbproject
│ ├── ant-deploy.xml
│ ├── build-impl.xml
│ ├── genfiles.properties
│ ├── private
│ │ └── private.properties
│ ├── project.properties
│ └── project.xml
└── src
└── conf
└── MANIFEST.MF
28 directories, 35 files
从：
https://docs.oracle.com/javaee/7/tutorial/ejb-gettingstarted001.htm
答案
在ConverterApplication-war和ConverterApplication-ejb模块的类路径中添加空beans.xml文件（在WEB-INF和META-INF文件夹中）。他们需要发现注入的组件。
另一答案
解：
package net.bounceme.dur.ejb;
import java.io.IOException;
import java.io.PrintWriter;
import java.math.BigDecimal;
import javax.ejb.EJB;
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(urlPatterns = "/")
public class ConverterServlet extends HttpServlet {
@EJB
ConverterBean converter;
protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
converter = new ConverterBean();
try (PrintWriter out = response.getWriter()) {
/* TODO output your page here. You may use following sample code. */
out.println("<!DOCTYPE html>");
out.println("<html>");
out.println("<head>");
out.println("<title>Servlet ConverterServlet</title>");
out.println("</head>");
out.println("<body>");
out.println("what is the amount?");
out.println("<h1>Servlet ConverterServlet at " + request.getContextPath() + "</h1>");
String stringAmount = "999";
out.println("amount is " + stringAmount);
out.println("<p>");
BigDecimal dollars = new BigDecimal(stringAmount);
out.println("dollars: " + dollars + " " + dollars.getClass());
out.println("<p>");
BigDecimal yen = converter.dollarToYen(dollars);
BigDecimal euros = converter.yenToEuro(yen);
out.println("never executed..");
out.println("yen");
out.println(yen);
out.println("<p>");
out.println("euros");
out.println(euros);
out.println("<p>");
out.println("</body>");
out.println("</html>");
}
}
// <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);
}
/**
* Returns a short description of the servlet.
*
* @return a String containing servlet description
*/
@Override
public String getServletInfo() {
return "Short description";
}// </editor-fold>
}
但是，不应该要求实例化bean。是正确还是错误？
看到：
NullPointerException in ejb injection
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