Java 使用RESTful Web服务：控制器Springboot错误

我正在研究如何在spring中使用rest控制器，我正在使用eclipse运行java/spring，我想问一下，在运行java时，我遇到了这样的错误。我已经试着寻找原因，等仍然没有找到解决办法。有人知道怎么修吗

Exception in thread "main" org.springframework.http.converter.HttpMessageConversionException: Type definition error: [simple type, class com.fasterxml.jackson.annotation.JsonIgnoreProperties$Value]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `com.fasterxml.jackson.annotation.JsonIgnoreProperties$Value` (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)
 at [Source: (PushbackInputStream); line: 1, column: 28] (through reference chain: hello.Quote["value"])
    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:100)
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:725)
    at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:680)
    at org.springframework.web.client.RestTemplate.getForObject(RestTemplate.java:332)
    at hello.Application.main(Application.java:15)
Caused by: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `com.fasterxml.jackson.annotation.JsonIgnoreProperties$Value` (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)
 at [Source: (PushbackInputStream); line: 1, column: 28] (through reference chain: hello.Quote["value"])
    at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:67)
    at com.fasterxml.jackson.databind.DeserializationContext.reportBadDefinition(DeserializationContext.java:1451)
    at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1027)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1290)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:326)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:159)
    at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:127)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:369)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:159)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4001)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3072)
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:235)
    ... 6 more

我的应用程序Java

package hello;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.client.RestTemplate;

public class Application {

    private static final Logger log = LoggerFactory.getLogger(Application.class);

    public static void main(String args[]) {
        RestTemplate restTemplate = new RestTemplate();
        Quote quote = restTemplate.getForObject("http://gturnquist-quoters.cfapps.io/api/random", Quote.class);
        log.info(quote.toString());
    }

}

引述爪哇语：

package hello;

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties.Value;

@JsonIgnoreProperties(ignoreUnknown = true)
public class Quote {

    private String type;
    private Value value;

    public Quote() {
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public Value getValue() {
        return value;
    }

    public void setValue(Value value) {
        this.value = value;
    }

    @Override
    public String toString() {
        return "Quote{" +
                "type='" + type + '\'' +
                ", value=" + value +
                '}';
    }
}

价值Java

package hello;

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;


@JsonIgnoreProperties(ignoreUnknown = true)

public class Value {

    private Long id;
    private String quote;

    public Value() {
    }

    public Long getId() {
        return this.id;
    }

    public String getQuote() {
        return this.quote;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public void setQuote(String quote) {
        this.quote = quote;
    }

    @Override
    public String toString() {
        return "Value{" +
                "id=" + id +
                ", quote='" + quote + '\'' +
                '}';
    }
}

Pom XML:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.resttemplate</groupId>
  <artifactId>hello1</artifactId>
  <packaging>war</packaging>
  <version>0.0.1-SNAPSHOT</version>
  <name>hello1 Maven Webapp</name>
  <url>http://maven.apache.org</url>
  <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.2.RELEASE</version>
    </parent>

    <properties>
        <java.version>1.8</java.version>
    </properties>
  <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-web</artifactId>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
        </dependency>
  </dependencies>
  <build>
    <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
  </build>
</project>

4.0.0
com.rest模板
你好
战争
0.0.1-快照
hello1 Maven Webapp
http://maven.apache.org
org.springframework.boot
spring启动程序父级
2.0.2.1发布
1.8
org.springframework.boot
弹簧靴起动器
org.springframework
弹簧网
com.fasterxml.jackson.core
杰克逊数据绑定
org.springframework.boot
springbootmaven插件

问题出在这一行

package hello;

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;

// Below you are importing wrong Value class
import com.fasterxml.jackson.annotation.JsonIgnoreProperties.Value;

您正在导入com.fasterxml.jackson.annotation.JsonIgnoreProperties.Value而不是Quote.java文件中的hello.Value类

用以下代码替换Quote.java文件

package hello;

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import hello.Value;

@JsonIgnoreProperties(ignoreUnknown = true)
public class Quote {

    private String type;
    private Value value;

    public Quote() {
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public Value getValue() {
        return value;
    }

    public void setValue(Value value) {
        this.value = value;
    }

    @Override
    public String toString() {
        return "Quote{" +
                "type='" + type + '\'' +
                ", value=" + value +
                '}';
    }
}

---

问题是Spring无法正确创建对象，因为类中没有匹配的构造函数

向类添加构造函数：

Value.java

public Value(Long id, String quote) {
 this.id = id;
 this.quote = quote;
}

public Quote(String type, Value value) {
 this.type= type;
 this.value= value;
}

Quote.java

public Value(Long id, String quote) {
 this.id = id;
 this.quote = quote;
}

public Quote(String type, Value value) {
 this.type= type;
 this.value= value;
}

上次我遇到了同样的问题：

---

在您的

Quote

类中，您正在使用

import com.fasterxml.jackson.annotation.JsonIgnoreProperties.Value

中的

Value

。我想那是错的。我猜您想使用在那里创建的

值。