java - Thymeleaf 电子邮件模板和 ConversionService

Question

我有一个 spring mvc 应用程序，我试图在其中将日期 LocalDate 呈现为字符串，对于普通 View 它可以工作但对于电子邮件它不起作用并抛出以下错误:

Caused by: org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [java.time.LocalDate] to type [java.lang.String]

代码:

import org.thymeleaf.context.Context;
import org.thymeleaf.spring4.SpringTemplateEngine;

@Service
public class EmailService {

    @Autowired
    private SpringTemplateEngine templateEngine;

    public String prepareTemplate() {
        // ...
        Context context = new Context();
        this.templateEngine.process(template, context);
    }
}

Answer 1

我调试了，发现如果我们使用新构造的上下文，它将创建另一个 ConversionService 实例，而不是使用 DefaultFormattingConversionService bean。

在thymeleaf spring的SpelVariableExpressionEvaulator中我们看到如下代码

        final Map<String,Object> contextVariables =
                computeExpressionObjects(configuration, processingContext);

        EvaluationContext baseEvaluationContext =
                (EvaluationContext) processingContext.getContext().getVariables().
                        get(ThymeleafEvaluationContext.THYMELEAF_EVALUATION_CONTEXT_CONTEXT_VARIABLE_NAME);

        if (baseEvaluationContext == null) {
            // Using a standard one as base: we are losing bean resolution and conversion service!!
            baseEvaluationContext = new StandardEvaluationContext();
        }

要解决这个问题，我们必须确保我们的上下文包含使用正确的转换服务初始化的 thymeleaf 评估上下文。

import org.thymeleaf.context.Context;
import org.thymeleaf.spring4.SpringTemplateEngine;
import org.springframework.core.convert.ConversionService;
import org.springframework.context.ApplicationContext;

@Service
public class EmailService {

    @Autowired
    private SpringTemplateEngine templateEngine;

    // Inject this
    @Autowired
    private ApplicationContext applicationContext;

    // Inject this
    @Autowired
    private ConversionService mvcConversionService;

    public String prepareTemplate() {
        // ...
        Context context = new Context();
        // Add the below two lines
        final ThymeleafEvaluationContext evaluationContext = new ThymeleafEvaluationContext(applicationContext, mvcConversionService);
        context.setVariable(ThymeleafEvaluationContext.THYMELEAF_EVALUATION_CONTEXT_CONTEXT_VARIABLE_NAME, evaluationContext);
        this.templateEngine.process(template, context);
    }
}

问题已解决。