java - java.lang.IllegalArgumentException：迭代变量不能为空
问题描述
在此处输入图像描述> 被困在这几天了。我相信这个问题必须做
与班级本身。或者所讨论的类与其列所在的类之间的关系。
这是我的课程： Mod
package com.matt.Keyword.models;
import javax.persistence.*;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Size;
@Entity
@Table(name = "Mods")
public class Mod {
@Id
@GeneratedValue
private int id;
@NotNull
private Integer role;
@NotNull
@Size(min = 1, message = "An entry is required")
private String entry;
@Column(name = "user_id")
private Integer userid;
public Mod(Integer role, String entry) {
this.role = role;
this.entry = entry;
}
public Mod() {
}
public int getId() {
return id;
}
public int getRole() {
return role;
}
public void setRole(Integer role) {
this.role = role;
}
public String getEntry() {
return entry;
}
public void setEntry(String entry) {
this.entry = entry;
}
public Integer getUserid() {
return userid;
}
public void setUserid(Integer userid) {
this.userid= userid;
}
}
帐户
package com.matt.Keyword.models;
import javax.persistence.*;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Size;
@Entity
public class Account {
@Id
@GeneratedValue
private int id;
@NotNull
@Size(min = 3, message = "Try again")
private String name;
@NotNull
@Size(min = 1, message = "A password is required")
private String password;
@Column(name = "user_id")
private Integer userid;
public Account(String name, String password) {
this.name = name;
this.password = password;
}
public Account() {
}
public int getId() {
return id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public Integer getUserid() {
return userid;
}
public void setUserid(Integer userid) {
this.userid = userid;
}
}
Account 和 Mod 类非常相似，并且与 user 类中的 user_id 列共享关系。
用户
package com.matt.Keyword.models;
import javax.persistence.*;
import javax.validation.constraints.Size;
import java.util.List;
@Entity
public class User {
@Id
@GeneratedValue
@Column(name = "user_id")
private int id;
@Size(min=3, message = "Try again")
private String email;
@Size(min=1, message = "A password is required")
private String password;
@OneToMany(cascade = CascadeType.ALL)
@JoinColumn(name = "user_id", referencedColumnName = "user_id")
private List<Account> accounts;
@OneToMany(cascade = CascadeType.ALL)
@JoinColumn(name = "user_id", referencedColumnName = "user_id")
private List<Mod> mods;
public User(String email, String password) {
this.email = email;
this.password = password;
}
public User() {}
public int getId() {
return id;
}
public void setId(Integer id){
this.id = id;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public List<Account> getAccounts() {
return accounts;
}
public void setAccounts(List<Account> accounts) {
this.accounts = accounts;
}
public List<Mod> getMods() {
return mods;
}
public void setMods(List<Mod> mods) {
this.mods = mods;
}
@Override
public String toString()
{
return email + " " + password;
}
}
当我从我的 mods 控制器加载索引页面时抛出异常。我正在使用百里香来渲染视图。这是我的模组控制器。Mods 数据库中保存了对象，并且在调试期间在此控制器中，传递给视图的属性包含已填充的 Mod 对象列表。 模组控制器
package com.matt.Keyword.controllers;
import com.matt.Keyword.models.Mod;
import com.matt.Keyword.models.User;
import com.matt.Keyword.models.data.ModDao;
import com.matt.Keyword.models.data.UserDao;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.validation.Errors;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import javax.servlet.http.HttpSession;
import javax.validation.Valid;
//test commit note
//second try
//third try
/**
* Created by LaunchCode
*/
@Controller
@RequestMapping("mod")
public class ModController {
@Autowired
private UserDao userDao;
@Autowired
private ModDao modDao;
@RequestMapping(value = "")
public String index(Model model, HttpSession session) {
if (session.getAttribute("currentUser") == null) {
return "redirect:/keyword/login";
}
session.getAttribute("currentUser");
model.addAttribute("title", "Mods");
model.addAttribute("mods", modDao.findAll());
return "mods/index";
}
@RequestMapping(value = "add", method = RequestMethod.GET)
public String displayModForm(Model model, HttpSession session) {
if (session.getAttribute("currentUser") == null) {
return "redirect:/keyword/login";
}
model.addAttribute("title", "Add a new mod");
model.addAttribute(new Mod());
return "mods/add";
}
@RequestMapping(value = "add", method = RequestMethod.POST)
public String processAddModForm(@ModelAttribute @Valid Mod newMod,
Errors errors, Model model, HttpSession session) {
if (errors.hasErrors()) {
model.addAttribute("title", "List of Mods");
return "mods/add";
}
User currentUser = (User) session.getAttribute("currentUser");
session.getId();
currentUser.setId(currentUser.getId());
newMod.setUserid(currentUser.getId());
modDao.save(newMod);
return "redirect:";
}
}
这是使用 thymeleaf 的 mod/index 页面。
模组/索引
<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org/">
<head th:replace="fragments :: head"></head>
<body class="container">
<h1 th:text="${title}">Default Title</h1>
<p th:unless="${mods} and ${mods.size()}">No current mods</p>
<nav th:replace="fragments :: navigation"></nav>
<p th:text="${session.currentUser.email}"></p>
<table class="table">
<tr>
<th>Type</th>
<th>Entry</th>
</tr>
<div th:if="${mods} != null">
<tr th:each="mod : ${mods}">
<div th:if="${mod.userid} == ${session.currentUser.id}">
<td th:text="${mod.role}"></td>
<td th:text="${mod.entry}"></td>
</div>
</tr>
</div>
</table>
</body>
</html>
该异常似乎与 for th:each 语句有关。特别是使用“mod”迭代器变量。这是完整错误的堆栈跟踪： Trace
There was an unexpected error (type=Internal Server Error, status=500).
An error happened during template parsing (template: "class path resource [templates/mods/index.html]")
org.thymeleaf.exceptions.TemplateInputException: An error happened during template parsing (template: "class path resource [templates/mods/index.html]")
at org.thymeleaf.templateparser.markup.AbstractMarkupTemplateParser.parse(AbstractMarkupTemplateParser.java:241)
at org.thymeleaf.templateparser.markup.AbstractMarkupTemplateParser.parseStandalone(AbstractMarkupTemplateParser.java:100)
at org.thymeleaf.engine.TemplateManager.parseAndProcess(TemplateManager.java:666)
at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1098)
at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1072)
at org.thymeleaf.spring5.view.ThymeleafView.renderFragment(ThymeleafView.java:362)
at org.thymeleaf.spring5.view.ThymeleafView.render(ThymeleafView.java:189)
at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1370)
at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1116)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1055)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:897)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882)
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.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
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:199)
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.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$SocketProcessor.doRun(NioEndpoint.java:1417)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)
Caused by: org.attoparser.ParseException: Error during execution of processor 'org.thymeleaf.standard.processor.StandardEachTagProcessor' (template: "mods/index" - line 21, col 17)
at org.attoparser.MarkupParser.parseDocument(MarkupParser.java:393)
at org.attoparser.MarkupParser.parse(MarkupParser.java:257)
at org.thymeleaf.templateparser.markup.AbstractMarkupTemplateParser.parse(AbstractMarkupTemplateParser.java:230)
... 52 more
Caused by: org.thymeleaf.exceptions.TemplateProcessingException: Error during execution of processor 'org.thymeleaf.standard.processor.StandardEachTagProcessor' (template: "mods/index" - line 21, col 17)
at org.thymeleaf.processor.element.AbstractAttributeTagProcessor.doProcess(AbstractAttributeTagProcessor.java:117)
at org.thymeleaf.processor.element.AbstractElementTagProcessor.process(AbstractElementTagProcessor.java:95)
at org.thymeleaf.util.ProcessorConfigurationUtils$ElementTagProcessorWrapper.process(ProcessorConfigurationUtils.java:633)
at org.thymeleaf.engine.ProcessorTemplateHandler.handleOpenElement(ProcessorTemplateHandler.java:1314)
at org.thymeleaf.engine.TemplateHandlerAdapterMarkupHandler.handleOpenElementEnd(TemplateHandlerAdapterMarkupHandler.java:304)
at org.thymeleaf.templateparser.markup.InlinedOutputExpressionMarkupHandler$InlineMarkupAdapterPreProcessorHandler.handleOpenElementEnd(InlinedOutputExpressionMarkupHandler.java:278)
at org.thymeleaf.standard.inline.OutputExpressionInlinePreProcessorHandler.handleOpenElementEnd(OutputExpressionInlinePreProcessorHandler.java:186)
at org.thymeleaf.templateparser.markup.InlinedOutputExpressionMarkupHandler.handleOpenElementEnd(InlinedOutputExpressionMarkupHandler.java:124)
at org.attoparser.HtmlElement.handleOpenElementEnd(HtmlElement.java:109)
at org.attoparser.HtmlMarkupHandler.handleOpenElementEnd(HtmlMarkupHandler.java:297)
at org.attoparser.MarkupEventProcessorHandler.handleOpenElementEnd(MarkupEventProcessorHandler.java:402)
at org.attoparser.ParsingElementMarkupUtil.parseOpenElement(ParsingElementMarkupUtil.java:159)
at org.attoparser.MarkupParser.parseBuffer(MarkupParser.java:710)
at org.attoparser.MarkupParser.parseDocument(MarkupParser.java:301)
... 54 more
Caused by: java.lang.IllegalArgumentException: Iteration variable cannot be null
at org.thymeleaf.util.Validate.notNull(Validate.java:37)
at org.thymeleaf.standard.expression.Each.<init>(Each.java:49)
at org.thymeleaf.standard.expression.EachUtils.composeEach(EachUtils.java:169)
at org.thymeleaf.standard.expression.EachUtils.internalParseEach(EachUtils.java:94)
at org.thymeleaf.standard.expression.EachUtils.parseEach(EachUtils.java:65)
at org.thymeleaf.standard.processor.StandardEachTagProcessor.doProcess(StandardEachTagProcessor.java:59)
at org.thymeleaf.processor.element.AbstractAttributeTagProcessor.doProcess(AbstractAttributeTagProcessor.java:74)
... 67 more
任何帮助表示赞赏。提前感谢您有时间看一下。
解决方案
这个问题被证明是一个相当棘手的问题。其决议的故事如下......
通过堆栈跟踪判断：
Caused by: java.lang.IllegalArgumentException: Iteration variable cannot be null
thymeleaf 模板中有一个迭代，其中有一个null变量被迭代。th:each我能找到的唯一用途是：
<div th:if="${mods} != null">
<tr th:each="mod : ${mods}">
...
</tr>
</div>
所以看起来这mods就是null问题th:each="mod : ${mods}"所在。
但是，使用<div th:if="${mods} != null">. 或者在那里？以下内容是否更有用：
<div th:if="${mods != null}">
IE。移动 以}使null检查在表达式内。
这没有帮助，因此modDao.findAll()检查了结果并找到了两个元素。所以它必须是别的东西。
回顾Thymeleaf 中的迭代基础知识表明，返回的集合可能不是可以迭代findAll()的受支持类型之一。th:each
所以这个集合被复制到Iterable一个不同的名字中，问题就解决了。
有趣的是，如果为迭代变量命名mod，问题仍然存在。原来mod是 hymeleaf 中的一个关键字，用于模块操作 ( %)。
最终，显然正确的代码存在两个问题：
- DAO 返回了一个集合，但不是一个可以被
th:each. mod是 Thymeleaf 中的关键字，不应用作变量名。
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