java - DateTimeFormatter 无法解析格式化日期

Question

我使用 DateTimeFormatter 来格式化日期。这是可行的，但是当我尝试将此格式化日期转换回日期时，我遇到了异常。

代码:

DateTimeFormatter weekOfYear = DateTimeFormatter.ofPattern("w/yyyy");

LocalDate localDate = LocalDate.now();
String dateString = weekOfYear.format(localDate);

localDate = LocalDate.parse(dateString, weekOfYear);

当我尝试解析它时出现异常:

java.time.format.DateTimeParseException: Text '50/2019' could not be parsed: Unable to obtain LocalDate from TemporalAccessor: {Year=2019, WeekOfWeekBasedYear[WeekFields[MONDAY,4]]=50},ISO of type java.time.format.Parsed

    at java.base/java.time.format.DateTimeFormatter.createError(DateTimeFormatter.java:2020)
    at java.base/java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1955)
    at java.base/java.time.LocalDate.parse(LocalDate.java:428)
    at DateTimeFormatterTest.weekOfYear(DateTimeFormatterTest.java:17)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:567)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
    at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)
    at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)
Caused by: java.time.DateTimeException: Unable to obtain LocalDate from TemporalAccessor: {Year=2019, WeekOfWeekBasedYear[WeekFields[MONDAY,4]]=50},ISO of type java.time.format.Parsed
    at java.base/java.time.LocalDate.from(LocalDate.java:396)
    at java.base/java.time.format.Parsed.query(Parsed.java:235)
    at java.base/java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1951)
    ... 24 more

Answer 1

无法解析日期，因为缺少日期部分。

所以我必须设置 dayOfWeek 的默认值:

DateTimeFormatter weekOfYear = new DateTimeFormatterBuilder().appendPattern("w/YYYY")
            .parseDefaulting(WeekFields.ISO.dayOfWeek(), 1).toFormatter();