Jsonschema2pojo从JSON生成Java类(Maven)

1.说明

jsonschema2pojo工具可以从JSON Schema(或示例JSON文件)生成Java类型，
并且可以配置生成Jackson 1.x,Jackson 2.x, Moshi 1.x或者Gson库的注解。
支持将jsonschema2pojo作为Maven插件、Ant任务、命令行工具、
Gradle插件或嵌入到Java应用程序中。
本文仅介绍Maven插件使用方式。
另外该工具还提供了在线版本,
可以在网站上直接使用：jsonschema2pojo online

2.创建Maven工程

Eclipse -> File -> New -> Other... -> Maven -> Maven Project
创建一个简单Maven工程，
pom.xml如下：

<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/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>edu.yuwen.util</groupId>
        <artifactId>json-file</artifactId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>
    <artifactId>generate-jsonschema2pojo</artifactId>
    <description>jsonschema2pojo generates Java types from JSON Schema (or example JSON)</description>
</project>

3.引入Maven插件

Maven方式生成Java类需要jsonschema2pojo-maven-plugin，
在pom.xml引入这个插件：

<build>
    <plugins>
        <plugin>
            <groupId>org.jsonschema2pojo</groupId>
            <artifactId>jsonschema2pojo-maven-plugin</artifactId>
            <version>1.0.2</version>
            <configuration>
                <sourceDirectory>${basedir}/src/main/resources/schema</sourceDirectory>
                <targetPackage>com.example.types</targetPackage>
            </configuration>
            <executions>
                <execution>
                    <goals>
                        <goal>generate</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

里面的配置项指定了JSON schema文件的目录，
以及生成的Java类的包路径。

4.新建JSON Schema

在src/main/resources/schema目录下
新建JSON Schema文件address.schema.json:

{
  "$id": "https://example.com/address.schema.json",
  "$schema": "http://json-schema.org/draft-07/schema#",
  "description": "An address similar to http://microformats.org/wiki/h-card",
  "type": "object",
  "properties": {
    "post-office-box": {
      "type": "string"
    },
    "extended-address": {
      "type": "string"
    },
    "street-address": {
      "type": "string"
    },
    "locality": {
      "type": "string"
    },
    "region": {
      "type": "string"
    },
    "postal-code": {
      "type": "string"
    },
    "country-name": {
      "type": "string"
    }
  },
  "required": [ "locality", "region", "country-name" ],
  "dependencies": {
    "post-office-box": [ "street-address" ],
    "extended-address": [ "street-address" ]
  }
}

5.运行Maven插件

运行Maven命令，
执行插件功能：
mvn generate-sources
或者
mvn package
Maven执行成功后，
会生成target/generated-sources/jsonschema2pojo/com/example/types/Address.java类。
推荐使用mvn generate-sources，
这样生成的target目录更干净些。

6.查看Address.java

package com.example.types;

import java.util.HashMap;
import java.util.Map;
import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;

/**
 * An address similar to http://microformats.org/wiki/h-card
 *
 */
@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({
    "post-office-box",
    "extended-address",
    "street-address",
    "locality",
    "region",
    "postal-code",
    "country-name"
})
public class AddressSchema {

    @JsonProperty("post-office-box")
    private String postOfficeBox;
    @JsonProperty("extended-address")
    private String extendedAddress;
    @JsonProperty("street-address")
    private String streetAddress;
    /**
     *
     * (Required)
     *
     */
    @JsonProperty("locality")
    private String locality;
    /**
     *
     * (Required)
     *
     */
    @JsonProperty("region")
    private String region;
    @JsonProperty("postal-code")
    private String postalCode;
    /**
     *
     * (Required)
     *
     */
    @JsonProperty("country-name")
    private String countryName;
    @JsonIgnore
    private Map<String, Object> additionalProperties = new HashMap<String, Object>();

    @JsonProperty("post-office-box")
    public String getPostOfficeBox() {
        return postOfficeBox;
    }

    @JsonProperty("post-office-box")
    public void setPostOfficeBox(String postOfficeBox) {
        this.postOfficeBox = postOfficeBox;
    }

    @JsonProperty("extended-address")
    public String getExtendedAddress() {
        return extendedAddress;
    }

    @JsonProperty("extended-address")
    public void setExtendedAddress(String extendedAddress) {
        this.extendedAddress = extendedAddress;
    }

    @JsonProperty("street-address")
    public String getStreetAddress() {
        return streetAddress;
    }

    @JsonProperty("street-address")
    public void setStreetAddress(String streetAddress) {
        this.streetAddress = streetAddress;
    }

    /**
     *
     * (Required)
     *
     */
    @JsonProperty("locality")
    public String getLocality() {
        return locality;
    }

    /**
     *
     * (Required)
     *
     */
    @JsonProperty("locality")
    public void setLocality(String locality) {
        this.locality = locality;
    }

    /**
     *
     * (Required)
     *
     */
    @JsonProperty("region")
    public String getRegion() {
        return region;
    }

    /**
     *
     * (Required)
     *
     */
    @JsonProperty("region")
    public void setRegion(String region) {
        this.region = region;
    }

    @JsonProperty("postal-code")
    public String getPostalCode() {
        return postalCode;
    }

    @JsonProperty("postal-code")
    public void setPostalCode(String postalCode) {
        this.postalCode = postalCode;
    }

    /**
     *
     * (Required)
     *
     */
    @JsonProperty("country-name")
    public String getCountryName() {
        return countryName;
    }

    /**
     *
     * (Required)
     *
     */
    @JsonProperty("country-name")
    public void setCountryName(String countryName) {
        this.countryName = countryName;
    }

    @JsonAnyGetter
    public Map<String, Object> getAdditionalProperties() {
        return this.additionalProperties;
    }

    @JsonAnySetter
    public void setAdditionalProperty(String name, Object value) {
        this.additionalProperties.put(name, value);
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append(AddressSchema.class.getName()).append('@').append(Integer.toHexString(System.identityHashCode(this))).append('[');
        sb.append("postOfficeBox");
        sb.append('=');
        sb.append(((this.postOfficeBox == null)?"<null>":this.postOfficeBox));
        sb.append(',');
        sb.append("extendedAddress");
        sb.append('=');
        sb.append(((this.extendedAddress == null)?"<null>":this.extendedAddress));
        sb.append(',');
        sb.append("streetAddress");
        sb.append('=');
        sb.append(((this.streetAddress == null)?"<null>":this.streetAddress));
        sb.append(',');
        sb.append("locality");
        sb.append('=');
        sb.append(((this.locality == null)?"<null>":this.locality));
        sb.append(',');
        sb.append("region");
        sb.append('=');
        sb.append(((this.region == null)?"<null>":this.region));
        sb.append(',');
        sb.append("postalCode");
        sb.append('=');
        sb.append(((this.postalCode == null)?"<null>":this.postalCode));
        sb.append(',');
        sb.append("countryName");
        sb.append('=');
        sb.append(((this.countryName == null)?"<null>":this.countryName));
        sb.append(',');
        sb.append("additionalProperties");
        sb.append('=');
        sb.append(((this.additionalProperties == null)?"<null>":this.additionalProperties));
        sb.append(',');
        if (sb.charAt((sb.length()- 1)) == ',') {
            sb.setCharAt((sb.length()- 1), ']');
        } else {
            sb.append(']');
        }
        return sb.toString();
    }

    @Override
    public int hashCode() {
        int result = 1;
        result = ((result* 31)+((this.postOfficeBox == null)? 0 :this.postOfficeBox.hashCode()));
        result = ((result* 31)+((this.streetAddress == null)? 0 :this.streetAddress.hashCode()));
        result = ((result* 31)+((this.postalCode == null)? 0 :this.postalCode.hashCode()));
        result = ((result* 31)+((this.locality == null)? 0 :this.locality.hashCode()));
        result = ((result* 31)+((this.countryName == null)? 0 :this.countryName.hashCode()));
        result = ((result* 31)+((this.additionalProperties == null)? 0 :this.additionalProperties.hashCode()));
        result = ((result* 31)+((this.extendedAddress == null)? 0 :this.extendedAddress.hashCode()));
        result = ((result* 31)+((this.region == null)? 0 :this.region.hashCode()));
        return result;
    }

    @Override
    public boolean equals(Object other) {
        if (other == this) {
            return true;
        }
        if ((other instanceof AddressSchema) == false) {
            return false;
        }
        AddressSchema rhs = ((AddressSchema) other);
        return (((((((((this.postOfficeBox == rhs.postOfficeBox)||((this.postOfficeBox!= null)&&this.postOfficeBox.equals(rhs.postOfficeBox)))&&((this.streetAddress == rhs.streetAddress)||((this.streetAddress!= null)&&this.streetAddress.equals(rhs.streetAddress))))&&((this.postalCode == rhs.postalCode)||((this.postalCode!= null)&&this.postalCode.equals(rhs.postalCode))))&&((this.locality == rhs.locality)||((this.locality!= null)&&this.locality.equals(rhs.locality))))&&((this.countryName == rhs.countryName)||((this.countryName!= null)&&this.countryName.equals(rhs.countryName))))&&((this.additionalProperties == rhs.additionalProperties)||((this.additionalProperties!= null)&&this.additionalProperties.equals(rhs.additionalProperties))))&&((this.extendedAddress == rhs.extendedAddress)||((this.extendedAddress!= null)&&this.extendedAddress.equals(rhs.extendedAddress))))&&((this.region == rhs.region)||((this.region!= null)&&this.region.equals(rhs.region))));
    }

}

7.引入插件依赖

当把Address.java放到工程的src/main/java目录下时，
Java编译会报错，
这是因为生成的类型依赖于Commons Lang的equals、hashCode和toString。
一些模式结构也会以Jackson注释的形式产生解析器提示。
需要在pom.xml中添加必要的依赖：

<dependencies>
    <dependency>
        <groupId>commons-lang</groupId>
        <artifactId>commons-lang</artifactId>
        <version>2.4</version>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.5.4</version>
    </dependency>
</dependencies>

8.新建JSON文件

上面演示了从JSON Schema生成Java类，
下面演示从JSON文件生成Java类，
首先在src\main\resources\json目录下，
新建一个JOSN文件person.json：

{
    "name":"bob",
    "age":33
}

9.修改插件配置

主要是指定了sourceType和sourceDirectory，
指定了源文件的格式是json和所在目录。

<build>
    <plugins>
        <plugin>
            <groupId>org.jsonschema2pojo</groupId>
            <artifactId>jsonschema2pojo-maven-plugin</artifactId>
            <version>1.0.2</version>
            <configuration>
                <sourceType>json</sourceType>
                <sourceDirectory>${basedir}/src/main/resources/json</sourceDirectory>
                <outputDirectory>${basedir}/src/main/java</outputDirectory>
                <targetPackage>com.example.types</targetPackage>
                <addCompileSourceRoot>true</addCompileSourceRoot>
                <annotationStyle>jackson2</annotationStyle>
            </configuration>
            <executions>
                <execution>
                    <goals>
                        <goal>generate</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

10.生成Person.java类

mvn generate-sources执行成功后，
会生成src/main/java/com/example/types/Person.java：

package com.example.types;

import java.util.HashMap;
import java.util.Map;
import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;

@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({
    "name",
    "age"
})
public class Person {

    @JsonProperty("name")
    private String name;
    @JsonProperty("age")
    private Integer age;
    @JsonIgnore
    private Map<String, Object> additionalProperties = new HashMap<String, Object>();

    @JsonProperty("name")
    public String getName() {
        return name;
    }

    @JsonProperty("name")
    public void setName(String name) {
        this.name = name;
    }

    @JsonProperty("age")
    public Integer getAge() {
        return age;
    }

    @JsonProperty("age")
    public void setAge(Integer age) {
        this.age = age;
    }

    @JsonAnyGetter
    public Map<String, Object> getAdditionalProperties() {
        return this.additionalProperties;
    }

    @JsonAnySetter
    public void setAdditionalProperty(String name, Object value) {
        this.additionalProperties.put(name, value);
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append(Person.class.getName()).append('@').append(Integer.toHexString(System.identityHashCode(this))).append('[');
        sb.append("name");
        sb.append('=');
        sb.append(((this.name == null)?"<null>":this.name));
        sb.append(',');
        sb.append("age");
        sb.append('=');
        sb.append(((this.age == null)?"<null>":this.age));
        sb.append(',');
        sb.append("additionalProperties");
        sb.append('=');
        sb.append(((this.additionalProperties == null)?"<null>":this.additionalProperties));
        sb.append(',');
        if (sb.charAt((sb.length()- 1)) == ',') {
            sb.setCharAt((sb.length()- 1), ']');
        } else {
            sb.append(']');
        }
        return sb.toString();
    }

    @Override
    public int hashCode() {
        int result = 1;
        result = ((result* 31)+((this.name == null)? 0 :this.name.hashCode()));
        result = ((result* 31)+((this.additionalProperties == null)? 0 :this.additionalProperties.hashCode()));
        result = ((result* 31)+((this.age == null)? 0 :this.age.hashCode()));
        return result;
    }

    @Override
    public boolean equals(Object other) {
        if (other == this) {
            return true;
        }
        if ((other instanceof Person) == false) {
            return false;
        }
        Person rhs = ((Person) other);
        return ((((this.name == rhs.name)||((this.name!= null)&&this.name.equals(rhs.name)))&&((this.additionalProperties == rhs.additionalProperties)||((this.additionalProperties!= null)&&this.additionalProperties.equals(rhs.additionalProperties))))&&((this.age == rhs.age)||((this.age!= null)&&this.age.equals(rhs.age))));
    }
}

11.插件配置项说明

1. sourceType:两个可选值，JSON Schema或者JSON文件，默认为JSON Schema。
2. sourceDirectory:源文件所在的目录，会将该目录下所有文件进行转换，不支持指定单个文件，如果不想全部转换，可以添加一个excludes节点。
3. outputDirectory:生成Java Pojo类的(根)目录，生成Java类的目录为此目录+包目录，默认值为target/generated-sources/jsonschema2pojo。
4. targetPackage:生成的Java pojo类的包路径。
5. addCompileSourceRoot:是否将输出目录作为项目的源码根目录。
6. annotationStyle:生成的(字段)注解样式，五个可选值：jackson1、jackson2、gson、moshi1和none，默认是jackson2，如果fastjson等工具不支持的，需要设置为none。

更多配置项的使用请参考：jsonschema2pojo-maven-plugin Optional Parameters

12.参考文章

使用maven根据JSON文件自动生成Java POJO类(Java Bean)源文件jsonschema2pojo github