blocks|key|2933710|text|你能测试一下这个结构吗。如果我没记错的话，你可以这样用它：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2933711|{
++++"applesRequest":+{
++++++++"applesDO":+[
++++++++++++{
++++++++++++++++"apple":+"Green+Apple"
++++++++++++},
++++++++++++{
++++++++++++++++"apple":+"Red+Apple"
++++++++++++}
++++++++]
++++}
}|code-block|syntax|javascript|2933712|其次，请将默认构造函数添加到每个类，这可能也会有所帮助。|2933713|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Can you please test this structure. If I remember correct you can use it this way:

<pre><code>{
 "applesRequest": {
 "applesDO": [
 {
 "apple": "Green Apple"
 },
 {
 "apple": "Red Apple"
 }
 ]
 }
}
</code></pre>

Second, please add default constructor to each class it also might help.

blocks|key|254053|text|所以，我终于意识到问题出在哪里。正如我所怀疑的，这不是杰克逊的配置问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|254054|实际上，问题出在ApplesDO类中：|offset|length|style|BOLD|254055|public+class+ApplesDO+{

++++private+String+apple;

++++public+String+getApple()+{
++++++++return+apple;
++++}

++++public+void+setApple(String+apple)+{
++++++++this.apple+=+apple;
++++}

++++public+ApplesDO(CustomType+custom)+{
++++++++//constructor+Code
++++}
}|code-block|syntax|javascript|254056|有一个为类定义的自定义构造函数，使其成为默认构造函数。引入一个虚拟构造函数使得这个错误消失：|254057|public+class+ApplesDO+{

++++private+String+apple;

++++public+String+getApple()+{
++++++++return+apple;
++++}

++++public+void+setApple(String+apple)+{
++++++++this.apple+=+apple;
++++}

++++public+ApplesDO(CustomType+custom)+{
++++++++//constructor+Code
++++}

++++//Introducing+the+dummy+constructor
++++public+ApplesDO()+{
++++}

}|254058|entityMap^0|0|8|8|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@$D|U|E|V|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|W|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|J|7|Y|8|@]|9|@]|A|$K|L]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

So, finally I realized what the problem is. It is not a Jackson configuration issue as I doubted.

Actually the problem was in ApplesDO Class:

<pre><code>public class ApplesDO {

 private String apple;

 public String getApple() {
 return apple;
 }

 public void setApple(String apple) {
 this.apple = apple;
 }

 public ApplesDO(CustomType custom) {
 //constructor Code
 }
}
</code></pre>

There was a custom constructor defined for the class making it the default constructor. Introducing a dummy constructor has made the error to go away:

<pre><code>public class ApplesDO {

 private String apple;

 public String getApple() {
 return apple;
 }

 public void setApple(String apple) {
 this.apple = apple;
 }

 public ApplesDO(CustomType custom) {
 //constructor Code
 }

 //Introducing the dummy constructor
 public ApplesDO() {
 }

}
</code></pre>

blocks|key|2933765|text|发生这种情况的原因如下：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2933766|2933767|您的内部类应该定义为static|ordered-list-item|offset|length|style|BOLD|2933768|2933769|私有静态类条件{//特定于杰克逊的}|2933770|可能是因为你的类中没有默认的构造函数(更新：看起来不是这样)|unordered-list-item|2933771|2933772|私有静态类条件{私有长id；公共条件(){}+//+setter和Getters+}|2933773|可能是您的setter未正确定义或不可见(例如私有setter)|2933774|2933775|entityMap^0|0|0|A|6|0|0|0|J|3|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|Z|8|@$F|10|G|11|H|I]]|9|@]|A|$]]|$1|J|3|-4|5|6|7|12|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|13|8|@]|9|@]|A|$]]|$1|M|3|N|5|O|7|14|8|@$F|15|G|16|H|I]]|9|@]|A|$]]|$1|P|3|-4|5|6|7|17|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|18|8|@]|9|@]|A|$]]|$1|S|3|T|5|O|7|19|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|1A|8|@]|9|@]|A|$]]|$1|V|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]]|W|$]]

This happens for these reasons:

<ol>
<li>your inner class should be defined as static

<pre><code>private static class Condition { //jackson specific 
}
</code></pre></li>
<li>It might be that you got no default constructor in your class (UPDATE: This seems not to be the case)

<pre><code>private static class Condition {
 private Long id;

 public Condition() {
 }

 // Setters and Getters
}
</code></pre></li>
<li>It could be your Setters are not defined properly or are not visible (e.g. private setter)</li>
</ol>

blocks|key|3148356|text|我想为此添加另一个不需要伪构造函数的解决方案。因为伪构造函数有点凌乱，随后会让人感到困惑。我们可以提供一个安全的构造函数，通过注释构造函数的参数，我们允许jackson确定构造函数参数和字段之间的映射。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3148357|所以下面的方法也是可行的。注意:注释中的字符串必须与字段名匹配。|3148358|import+com.fasterxml.jackson.annotation.JsonProperty;
public+class+ApplesDO+{

++++++++private+String+apple;

++++++++public+String+getApple()+{
++++++++++++return+apple;
++++++++}

++++++++public+void+setApple(String+apple)+{
++++++++++++this.apple+=+apple;
++++++++}

++++++++public+ApplesDO(CustomType+custom){
++++++++++++//constructor+Code
++++++++}

++++++++public+ApplesDO(@JsonProperty("apple")String+apple)+{
++++++++}

}|code-block|syntax|javascript|3148359|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I would like to add another solution to this that does not require a dummy constructor. Since dummy constructors are a bit messy and subsequently confusing. We can provide a safe constructor and by annotating the constructor arguments we allow jackson to determine the mapping between constructor parameter and field.

so the following will also work. Note the string inside the annotation must match the field name.

<pre><code>import com.fasterxml.jackson.annotation.JsonProperty;
public class ApplesDO {

 private String apple;

 public String getApple() {
 return apple;
 }

 public void setApple(String apple) {
 this.apple = apple;
 }

 public ApplesDO(CustomType custom){
 //constructor Code
 }

 public ApplesDO(@JsonProperty("apple")String apple) {
 }

}
</code></pre>

blocks|key|2933807|text|经验法则：为您用作映射类的每个类添加一个默认构造函数。你错过了这一点，问题就出现了！|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2933808|只需添加默认构造函数，它就应该可以工作了。|2933809|entityMap^0|0|4|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|M|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|N|8|@]|D|@]|E|$]]]|I|$]]

Thumb Rule: Add a default constructor for each class you used as a mapping class. You missed this and issue arise! 
Simply add default constructor and it should work.

blocks|key|250368|text|当我遇到这个问题时，它是试图使用内部类作为DO的结果。内部类的构造(静默地)需要封闭类的一个实例--这对于Jackson是不可用的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|250369|在这种情况下，将内部类移动到它自己的.java文件解决了这个问题。|250370|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

When I ran into this problem, it was a result of trying to use an inner class to serve as the DO. Construction of the inner class (silently) required an instance of the enclosing class -- which wasn't available to Jackson.

In this case, moving the inner class to its own .java file fixed the problem.

blocks|key|250372|text|失败的自定义jackson序列化程序/反序列化程序也可能是问题。虽然这不是你的情况，但值得一提的是。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|250373|我遇到了同样的例外，情况就是这样。|250374|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Failing custom jackson Serializers/Deserializers could also be the problem. Though it's not your case, it's worth mentioning.

I faced the same exception and that was the case.

blocks|key|3148413|text|您必须认识到Jackson有哪些可用于反序列化的选项。在Java中，编译后的代码中不存在方法参数名称。这就是为什么Jackson通常不能使用构造函数来创建一个定义良好的对象，并且一切都已经设置好了。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3148414|因此，如果有一个空的构造函数和setter函数，它就会使用空的构造函数和setter函数。如果没有setter，则使用一些黑魔法(反射)来完成此操作。|3148415|如果你想对Jackson使用构造函数，你必须使用@PiersyP在他的回答中提到的注释。您还可以使用构建器模式。如果你遇到一些异常，祝你好运。杰克逊的错误处理很糟糕，很难理解错误消息中的胡言乱语。|3148416|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

You must realize what options Jackson has available for deserialization. In Java, method argument names are not present in the compiled code. That's why Jackson can't generally use constructors to create a well-defined object with everything already set.

So, if there is an empty constructor and there are also setters, it uses the empty constructor and setters. If there are no setters, some dark magic (reflections) is used to do it.

If you want to use a constructor with Jackson, you must use the annotations as mentioned by @PiersyP in his answer. You can also use a builder pattern. If you encounter some exceptions, good luck. Error handling in Jackson sucks big time, it's hard to understand that gibberish in error messages.

blocks|key|255390|text|如果开始批注构造函数，则必须批注所有字段。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|255391|注意，我的Staff.name字段被映射到JSON+string中的"ANOTHER_NAME“。|255392|+++++String+jsonInString="{\"ANOTHER_NAME\":\"John\",\"age\":\"17\"}";
+++++ObjectMapper+mapper+=+new+ObjectMapper();
+++++Staff+obj+=+mapper.readValue(jsonInString,+Staff.class);
+++++//+print+to+screen

+++++public+static+class+Staff+{
+++++++public+String+name;
+++++++public+Integer+age;
+++++++public+Staff()+{+++++++++
+++++++}++++++++

+++++++//@JsonCreator+-+don't+need+this
+++++++public+Staff(@JsonProperty("ANOTHER_NAME")+String+++n,@JsonProperty("age")+Integer+a)+{
++++++++name=n;age=a;
+++++++}++++++++
++++}|code-block|syntax|javascript|255393|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

If you start annotating constructor, you must annotate all fields.

Notice, my Staff.name field is mapped to "ANOTHER_NAME" in JSON string.

<pre><code> String jsonInString="{\"ANOTHER_NAME\":\"John\",\"age\":\"17\"}";
 ObjectMapper mapper = new ObjectMapper();
 Staff obj = mapper.readValue(jsonInString, Staff.class);
 // print to screen

 public static class Staff {
 public String name;
 public Integer age;
 public Staff() { 
 } 

 //@JsonCreator - don't need this
 public Staff(@JsonProperty("ANOTHER_NAME") String n,@JsonProperty("age") Integer a) {
 name=n;age=a;
 } 
 }
</code></pre>

blocks|key|2934034|text|在映射json时，您必须在我们的模型class.So中创建虚拟的空构造函数，它是由setter方法设置的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2934035|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

You have to create dummy empty constructor in our model class.So while mapping json, it set by setter method.

blocks|key|250503|text|对我来说，这曾经是可行的，但是升级库导致了这个问题的出现。问题是有一个这样的类：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|250504|package+example.counter;

import+javax.validation.constraints.NotNull;

import+lombok.Data;

@Data
public+class+CounterRequest+{
++++@NotNull
++++private+final+Integer+int1;

++++@NotNull
++++private+final+Integer+int2;
}|code-block|syntax|javascript|250505|使用lombok：|250506|<dependency>
++++<groupId>org.projectlombok</groupId>
++++<artifactId>lombok</artifactId>
++++<version>1.18.0</version>
</dependency>|250507|回落到|250508|<dependency>
++++<groupId>org.projectlombok</groupId>
++++<artifactId>lombok</artifactId>
++++<version>1.16.10</version>
</dependency>|250509|已修复此问题。不知道为什么，但想记录下来以备将来之需。|250510|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

For me, this used to work, but upgrading libraries caused this issue to appear. Problem was having a class like this:

<pre><code>package example.counter;

import javax.validation.constraints.NotNull;

import lombok.Data;

@Data
public class CounterRequest {
 @NotNull
 private final Integer int1;

 @NotNull
 private final Integer int2;
}
</code></pre>

Using lombok:

<pre><code>&lt;dependency&gt;
 &lt;groupId&gt;org.projectlombok&lt;/groupId&gt;
 &lt;artifactId&gt;lombok&lt;/artifactId&gt;
 &lt;version&gt;1.18.0&lt;/version&gt;
&lt;/dependency&gt;
</code></pre>

Falling back to

<pre><code>&lt;dependency&gt;
 &lt;groupId&gt;org.projectlombok&lt;/groupId&gt;
 &lt;artifactId&gt;lombok&lt;/artifactId&gt;
 &lt;version&gt;1.16.10&lt;/version&gt;
&lt;/dependency&gt;
</code></pre>

Fixed the issue. Not sure why, but wanted to document it for future.

blocks|key|254274|text|通常，这个错误是因为我们没有将默认构造函数设为。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|254275|但在我的例子中：|254276|这个问题之所以出现，是因为我让在父类中使用object类。|254277|这浪费了我一整天。|254278|entityMap^0|C|B|0|0|F|3|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Q|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|R|8|@$9|S|A|T|B|C]]|D|@]|E|$]]|$1|J|3|K|5|6|7|U|8|@]|D|@]|E|$]]|$1|L|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|M|$]]

Generally, this error comes because we don’t make default constructor. 
But in my case: 
The issue was coming only due to I have made used object class inside parent class. 
This has wasted my whole day.

blocks|key|252155|text|关于上一次发布，我在使用Lombok+1.18时遇到了同样的问题。*产生了这个问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|252156|我的解决方案是添加@NoArgsConstructor+(不带参数的构造函数)，因为@Data默认包含@RequiredArgsConstructor+(带参数的构造函数)。|252157|龙目岛文档https://projectlombok.org/features/all|offset|length|252158|这就解决了这个问题：|252159|package+example.counter;

import+javax.validation.constraints.NotNull;

import+lombok.Data;

@Data
@NoArgsConstructor
public+class+CounterRequest+{
++++@NotNull
++++private+final+Integer+int1;

++++@NotNull
++++private+final+Integer+int2;
}|code-block|syntax|javascript|252160|entityMap|0|LINK|mutability|MUTABLE|url|https://projectlombok.org/features/all^0|0|0|5|12|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Y|8|@]|9|@$F|Z|G|10|1|11]]|A|$]]|$1|H|3|I|5|6|7|12|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|13|8|@]|9|@]|A|$M|N]]|$1|O|3|-4|5|6|7|14|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|V]]]]

Regarding the last publication I had the same problem where using Lombok 1.18.* generated the problem.

My solution was to add @NoArgsConstructor (constructor without parameters), since @Data includes by default @RequiredArgsConstructor (Constructor with parameters).

lombok Documentation
<a href="https://projectlombok.org/features/all" rel="noreferrer">https://projectlombok.org/features/all</a>

That would solve the problem:

<pre><code>package example.counter;

import javax.validation.constraints.NotNull;

import lombok.Data;

@Data
@NoArgsConstructor
public class CounterRequest {
 @NotNull
 private final Integer int1;

 @NotNull
 private final Integer int2;
}
</code></pre>

blocks|key|2934168|text|将默认构造函数添加到所有实体类|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2934169|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Add default constructors to all the entity classes

I am getting the following error when trying to get a JSON request and process it:

<blockquote>
 org.codehaus.jackson.map.JsonMappingException: No suitable constructor found for type [simple type, class com.myweb.ApplesDO]: can not instantiate from JSON object (need to add/enable type information?)
</blockquote>

Here is the JSON I am trying to send:

<pre class="lang-json prettyprint-override"><code>{
 "applesDO" : [
 {
 "apple" : "Green Apple"
 },
 {
 "apple" : "Red Apple"
 }
 ]
}
</code></pre>

In Controller, I have the following method signature:

<pre><code>@RequestMapping("showApples.do")
public String getApples(@RequestBody final AllApplesDO applesRequest){
 // Method Code
}
</code></pre>

AllApplesDO is a wrapper of ApplesDO :

<pre><code>public class AllApplesDO {

 private List&lt;ApplesDO&gt; applesDO;

 public List&lt;ApplesDO&gt; getApplesDO() {
 return applesDO;
 }

 public void setApplesDO(List&lt;ApplesDO&gt; applesDO) {
 this.applesDO = applesDO;
 }
}
</code></pre>

ApplesDO:

<pre><code>public class ApplesDO {

 private String apple;

 public String getApple() {
 return apple;
 }

 public void setApple(String appl) {
 this.apple = apple;
 }

 public ApplesDO(CustomType custom){
 //constructor Code
 }
}
</code></pre>

I think that Jackson is unable to convert JSON into Java objects for subclasses. Please help with the configuration parameters for Jackson to convert JSON into Java Objects. I am using Spring Framework.

EDIT: Included the major bug that is causing this problem in the above sample class - Please look accepted answer for solution.

JsonMappingException: No suitable constructor found for type [simple type, class ]: can not instantiate from JSON object

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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在尝试获取JSON请求并对其进行处理时，我遇到以下错误：JSON org.codehaus.jackson.map.JsonMappingException:找不到适用于类型简单类型的构造函数，类com.myweb.ApplesDO:无法从对象实例化(需要添加/启用类型信息？)这是我尝试发送的JSON：{  "appl...

问JsonMappingException:找不到适用于类型[简单类型，类]的构造函数:无法从JSON对象实例化
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问JsonMappingException:找不到适用于类型[简单类型，类]的构造函数:无法从JSON对象实例化
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