Thymeleaf 迭代对象列表 [英] Thymeleaf iteration over list of objects

问题描述

我在迭代 Thymeleaf 中的对象列表时遇到问题.这是我的 HTML:

I have a problem, while I am iterating over a list of object in Thymeleaf. Here is my HTML:

<input th:each="a,iterStatus : currentQuestion.answers" type="radio" name="answer" th:text="${a.answer}" th:value="${iterStatus.index}"></input>

这是控制器类:

@RequestMapping(value={ "/exam", "/exam/" }, method = RequestMethod.GET)
public String exam(Model model){

    if (!sessionPreferences.isExamStarted()){
        sessionPreferences.setQuestionList(questionService.list(Questions.findAll().paginate(0, 5).loadWith("answers")));
        sessionPreferences.setCurrentQuestion(questionService.uniqueObject(Questions.findAll().withId(1L).loadWith("answers")));
    }
    model.addAttribute("currentQuestion", sessionPreferences.getCurrentQuestion());
    sessionPreferences.setExamStarted(true);
    System.out.println("TRUE!");
    System.out.println(sessionPreferences.getCurrentQuestion().getAnswers().size());
    System.out.println(sessionPreferences.getCurrentQuestion().getAnswers().get(0));
    return "exam";
}

这是 SessionPreferences 类:

Here is SessionPreferences class:

@Component
@Scope(value="session", proxyMode = ScopedProxyMode.TARGET_CLASS)
public class SessionPreferences implements Serializable {

private static final long serialVersionUID = -3875093750700352970L;

@Setter
private String displayName;

@Setter @Getter
private Question currentQuestion;

@Getter @Setter
private boolean examStarted;

@Getter @Setter
private Map<Question, Integer> selections = new LinkedHashMap<Question, Integer>();

@Getter @Setter
private List<Question> questionList = new ArrayList<Question>(5);


public String getDisplayName() {
    if(StringUtils.isBlank(displayName)){
        displayName = SecurityUtils.getLoggedUsername();
    }
    return displayName;
  }
}

我们有问题模型类:

@Entity
@Table(name = "questions")
public class Question extends BaseEntity<Long> {

private static final long serialVersionUID = -7066617446892759711L;
public static final int DESCRIPTION_MAX_LENGTH = 5120;
public static final int OPTIONS_MAX_LENGTH = 4 * 5120;

public Question() {
};

public Question(String questionDescription, List<Answer> answers) {
    this.questionDescription = questionDescription;
};

@Id
@GeneratedValue
@Getter
@Setter
private Long id;

@Getter
@Setter
@Column(length = DESCRIPTION_MAX_LENGTH, nullable = false, name = "question_description")
private String questionDescription;

@Getter
@Setter
@OneToMany(mappedBy = "question", targetEntity = Answer.class, cascade = CascadeType.ALL)
private List<Answer> answers = new ArrayList<>();

@Getter
@Setter
@Column(nullable = false, name = "correct_answer_id")
private Answer correctAnswerIndex;
}

还有答案类:

@Entity
@Table(name="answers")
public class Answer extends BaseEntity<Long>{

private static final long serialVersionUID = -6119650375719671237L;

public Answer(){};

public Answer(String answer){
    this.answer = answer;
};

@Id
@GeneratedValue
@Getter @Setter
private Long id;

@Getter @Setter
private String answer;

@ManyToOne
@JoinColumn(name = "question_id", updatable=false)
@Getter @Setter
private Question question;

}

DAO 层和 Service 层工作正常，因此在使用 Thymeleaf 进行迭代时访问 Answer 对象中的 String answer 存在问题.

DAO layer and Service layer work fine, so it's a problem in accessing String answer in Answer object while iterating using Thymeleaf.

我有以下错误:

SEVERE: Servlet.service() for servlet [spring] in context with path [] threw exception [Request processing failed; nested exception is org.thymeleaf.exceptions.TemplateProcessingException: Exception evaluating SpringEL expression: "a.answer" (exam:99)] with root cause
  org.springframework.expression.spel.SpelEvaluationException: EL1008E:(pos 2): Field or property 'answer' cannot be found on object of type 'java.lang.String'

有什么想法吗???

P.s 三个 syso 结果:TRUE!, 4, Object..

P.s Three syso resulted in: TRUE!, 4, Object..

推荐答案

th:each 属性的语法有问题，currentQuestion.answers 应该是包装到表达式求值 (${...}) 组中.

There is a problem in the syntax for th:each attribute, as currentQuestion.answers should be wrapped into expression evaluation (${...}) group.

正确的版本:

<input th:each="a,iterStatus : ${currentQuestion.answers}" type="radio" name="answer" th:text="${a.answer}" th:value="${iterStatus.index}"></input>

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