Jackson進行json轉對象時，遇到的字符串轉日期的異常處理（Can not deserialize value of type Date from String）

出現的場景：

服務端通過springmvc寫了一個對外的接口，返回一個json字符串，其中該json帶有日期，格式爲yyyy-MM-dd HH:mm:ss

客戶端通過feign調用該http接口，指定返回值爲一個Dto，Dto中日期的字段爲Date類型

客戶端調用該接口後拋異常了。

報錯異常如下：

feign.codec.DecodeException: JSON parse error: Can not deserialize value of type java.util.Date from String "2018-03-07 16:18:35": not a valid representation (error: Failed to parse Date value '2018-03-07 16:18:35': Can not parse date "2018-03-07 16:18:35Z": while it seems to fit format 'yyyy-MM-dd'T'HH:mm:ss.SSS'Z'', parsing fails (leniency? null)); nested exception is com.fasterxml.jackson.databind.exc.InvalidFormatException: Can not deserialize value of type java.util.Date from String "2018-03-07 16:18:35": not a valid representation (error: Failed to parse Date value '2018-03-07 16:18:35': Can not parse date "2018-03-07 16:18:35Z": while it seems to fit format 'yyyy-MM-dd'T'HH:mm:ss.SSS'Z'', parsing fails (leniency? null))
 at [Source: java.io.PushbackInputStream@4615bc00; line: 1, column: 696] (through reference chain: com.RestfulDataBean["data"]->java.util.ArrayList[0]->com.entity.XxxDto["createTime"])
	at feign.SynchronousMethodHandler.decode(SynchronousMethodHandler.java:169)
	at feign.SynchronousMethodHandler.executeAndDecode(SynchronousMethodHandler.java:133)
	at feign.SynchronousMethodHandler.invoke(SynchronousMethodHandler.java:76)
	at feign.ReflectiveFeign$FeignInvocationHandler.invoke(ReflectiveFeign.java:103)
	at com.sun.proxy.$Proxy138.queryMonitorByTime(Unknown Source)
	at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
	at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:738)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
	at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99)
	at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:282)
	at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
	at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:673)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	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.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
	at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
	at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:252)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:94)
	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.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
	at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:191)
	at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
	at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
	at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
Caused by: org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Can not deserialize value of type java.util.Date from String "2018-03-07 16:18:35": not a valid representation (error: Failed to parse Date value '2018-03-07 16:18:35': Can not parse date "2018-03-07 16:18:35Z": while it seems to fit format 'yyyy-MM-dd'T'HH:mm:ss.SSS'Z'', parsing fails (leniency? null)); nested exception is com.fasterxml.jackson.databind.exc.InvalidFormatException: Can not deserialize value of type java.util.Date from String "2018-03-07 16:18:35": not a valid representation (error: Failed to parse Date value '2018-03-07 16:18:35': Can not parse date "2018-03-07 16:18:35Z": while it seems to fit format 'yyyy-MM-dd'T'HH:mm:ss.SSS'Z'', parsing fails (leniency? null))
 at [Source: java.io.PushbackInputStream@4615bc00; line: 1, column: 696] (through reference chain: com.RestfulDataBean["data"]->java.util.ArrayList[0]->com.XxxDto["createTime"])
	at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:238)
	at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.read(AbstractJackson2HttpMessageConverter.java:223)
	at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:96)
	at org.springframework.cloud.netflix.feign.support.SpringDecoder.decode(SpringDecoder.java:59)
	at org.springframework.cloud.netflix.feign.support.ResponseEntityDecoder.decode(ResponseEntityDecoder.java:47)
	at feign.SynchronousMethodHandler.decode(SynchronousMethodHandler.java:165)
	... 45 more
Caused by: com.fasterxml.jackson.databind.exc.InvalidFormatException: Can not deserialize value of type java.util.Date from String "2018-03-07 16:18:35": not a valid representation (error: Failed to parse Date value '2018-03-07 16:18:35': Can not parse date "2018-03-07 16:18:35Z": while it seems to fit format 'yyyy-MM-dd'T'HH:mm:ss.SSS'Z'', parsing fails (leniency? null))
 at [Source: java.io.PushbackInputStream@4615bc00; line: 1, column: 696] (through reference chain: com.RestfulDataBean["data"]->java.util.ArrayList[0]->com.XxxDto["createTime"])
	at com.fasterxml.jackson.databind.exc.InvalidFormatException.from(InvalidFormatException.java:74)
	at com.fasterxml.jackson.databind.DeserializationContext.weirdStringException(DeserializationContext.java:1410)
	at com.fasterxml.jackson.databind.DeserializationContext.handleWeirdStringValue(DeserializationContext.java:926)
	at com.fasterxml.jackson.databind.deser.std.StdDeserializer._parseDate(StdDeserializer.java:819)
	at com.fasterxml.jackson.databind.deser.std.StdDeserializer._parseDate(StdDeserializer.java:788)
	at com.fasterxml.jackson.databind.deser.std.DateDeserializers$DateBasedDeserializer._parseDate(DateDeserializers.java:172)
	at com.fasterxml.jackson.databind.deser.std.DateDeserializers$DateDeserializer.deserialize(DateDeserializers.java:259)
	at com.fasterxml.jackson.databind.deser.std.DateDeserializers$DateDeserializer.deserialize(DateDeserializers.java:242)
	at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:504)
	at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:104)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:357)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:148)
	at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:287)
	at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:259)
	at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:26)
	at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:504)
	at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:104)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:357)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:148)
	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3814)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2938)
	at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:235)
	... 50 more

從異常信息中我們可以看出，是在AbstractJackson2HttpMessageConverter類中調用了readJavaType方法之後拋的異常
一步一步往下深入，我們找到了最關鍵的地方，在DeserializationContext類的_parseDate方法中，執行了df.parse(dateStr)之後拋異常了

public Date parseDate(String dateStr) throws IllegalArgumentException
{
    try {
        DateFormat df = getDateFormat();
        // 這行代碼報錯了
        return df.parse(dateStr);
    } catch (ParseException e) {
        throw new IllegalArgumentException(String.format(
                "Failed to parse Date value '%s': %s", dateStr, e.getMessage()));
    }
}

DeserializationContext是jackson的一個反序列化的一個上下文，那麼它的DateFormat是從哪來的呢?我們再來看下getDateFormat的源碼

protected DateFormat getDateFormat()
{
    if (_dateFormat != null) {
        return _dateFormat;
    }
    DateFormat df = _config.getDateFormat();
    _dateFormat = df = (DateFormat) df.clone();
    return df;
}

DateFormat又是從MapperConfig而來，我們再看下config.getDateFormat()的源碼

public final DateFormat getDateFormat() { return _base.getDateFormat(); }

我們知道，SpringMvc就是通過AbstractJackson2HttpMessageConverter類來整合jackson的，該類維護jackson的ObjectMapper，而ObjectMapper又是通過MapperConfig來進行配置的
由此可見，本異常就是因爲ObjectMapper中的DateFormat無法對yyyy-MM-dd HH:mm:ss格式的字符串進行轉換所導致的
異常說的值服務器返回了一個帶有日期的json，日期的形式是字符串2018-03-07 16:18:35，jackson無法將該字符串轉成一個Date對象，網上查資料，上面說的是jackson只支持以下幾種日期格式：

"yyyy-MM-dd'T'HH:mm:ss.SSSZ"；

"yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"；
"yyyy-MM-dd";

"EEE, dd MMM yyyy HH:mm:ss zzz";

long類型的時間戳
去掉服務端的以下兩個配置，讓日期返回時間戳，結果就沒報錯了

#spring.jackson.date-format=yyyy-MM-dd HH:mm:ss
#spring.jackson.time-zone=Asia/Chongqing

由於服務端在其他的地方有可能和這裏的配置耦合了，也就是說其他地方有可能要用到的是yyyy-MM-dd HH:mm:ss這一日期格式而不是時間戳的格式，所以這個配置肯定是不能修改的。
jackson竟然不支持yyyy-MM-dd HH:mm:ss的這種格式，肯定很不爽啦，所以下面就要開始來研究怎麼讓jackson支持這種格式了。
要讓jackson支持這種格式，那麼就必須修改ObjectMapper中的DateFormat，因爲在ObjectMapper中，DateFormat的默認實現類是StdDateFormat，StdDateFormat也就只兼容了我們上述所說的幾種格式

首先我們先使用裝飾模式來創建一個支持yyyy-MM-dd HH:mm:ss格式的DateFormat如下

 
import java.text.DateFormat;
import java.text.FieldPosition;
import java.text.ParseException;
import java.text.ParsePosition;
import java.text.SimpleDateFormat;
import java.util.Date;
 
public class MyDateFormat extends DateFormat {
 
	private DateFormat dateFormat;
 
	private SimpleDateFormat format1 = new SimpleDateFormat("yyy-MM-dd HH:mm:ss");
 
	public MyDateFormat(DateFormat dateFormat) {
		this.dateFormat = dateFormat;
	}
 
	@Override
	public StringBuffer format(Date date, StringBuffer toAppendTo, FieldPosition fieldPosition) {
		return dateFormat.format(date, toAppendTo, fieldPosition);
	}
 
	@Override
	public Date parse(String source, ParsePosition pos) {
 
		Date date = null;
 
		try {
 
			date = format1.parse(source, pos);
		} catch (Exception e) {
 
			date = dateFormat.parse(source, pos);
		}
 
		return date;
	}
 
	// 主要還是裝飾這個方法
	@Override
	public Date parse(String source) throws ParseException {
 
		Date date = null;
 
		try {
			
			// 先按我的規則來
			date = format1.parse(source);
		} catch (Exception e) {
 
			// 不行，那就按原先的規則吧
			date = dateFormat.parse(source);
		}
 
		return date;
	}
 
	// 這裏裝飾clone方法的原因是因爲clone方法在jackson中也有用到
	@Override
	public Object clone() {
		Object format = dateFormat.clone();
		return new MyDateFormat((DateFormat) format);
	}
}

DateFormat有了，接下來的任務就是讓ObjectMapper使用我的這個DateFormat了，在config類中定義如下（本案例基於springboot）

@Configuration
public class WebConfig {
 
	@Autowired
	private Jackson2ObjectMapperBuilder jackson2ObjectMapperBuilder;
	
	@Bean
	public MappingJackson2HttpMessageConverter MappingJsonpHttpMessageConverter() {
 
		ObjectMapper mapper = jackson2ObjectMapperBuilder.build();
 
		// ObjectMapper爲了保障線程安全性，裏面的配置類都是一個不可變的對象
		// 所以這裏的setDateFormat的內部原理其實是創建了一個新的配置類
		DateFormat dateFormat = mapper.getDateFormat();
		mapper.setDateFormat(new MyDateFormat(dateFormat));
 
		MappingJackson2HttpMessageConverter mappingJsonpHttpMessageConverter = new MappingJackson2HttpMessageConverter(
				mapper);
		return mappingJsonpHttpMessageConverter;
	}
}

配置了上述代碼之後，問題成功解決。

3、爲什麼往spring容器中注入MappingJackson2HttpMessageConverter，springMvc就會用這個Converter呢？

查看springboot的源代碼如下：

@Configuration
class JacksonHttpMessageConvertersConfiguration {
 
	@Configuration
	@ConditionalOnClass(ObjectMapper.class)
	@ConditionalOnBean(ObjectMapper.class)
	@ConditionalOnProperty(name = HttpMessageConvertersAutoConfiguration.PREFERRED_MAPPER_PROPERTY, havingValue = "jackson", matchIfMissing = true)
	protected static class MappingJackson2HttpMessageConverterConfiguration {
 
		@Bean
		@ConditionalOnMissingBean(value = MappingJackson2HttpMessageConverter.class, ignoredType = {
				"org.springframework.hateoas.mvc.TypeConstrainedMappingJackson2HttpMessageConverter",
				"org.springframework.data.rest.webmvc.alps.AlpsJsonHttpMessageConverter" })
		public MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter(
				ObjectMapper objectMapper) {
			return new MappingJackson2HttpMessageConverter(objectMapper);
		}
 
}

默認配置爲，當spring容器中沒有MappingJackson2HttpMessageConverter這個實例的時候纔會被創建
springboot的思想是約定優於配置，也就是說，springboot默認幫我們配好了spring mvc的Converter，如果我們沒有自定義Converter的話，那麼框架就會幫我們創建一個，如果我們有自定義的話，那麼springboot就直接使用我們所註冊的bean進行綁定

Jackson進行json轉對象時，遇到的字符串轉日期的異常處理（Can not deserialize value of type Date from String）

3、爲什麼往spring容器中注入MappingJackson2HttpMessageConverter，springMvc就會用這個Converter呢？

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