jaxb xsd生成xml_使用JAXB和Jackson从XSD生成JSON模式

jaxb xsd生成xml

在本文中，我演示了一种从XML Schema （XSD）生成JSON Schema的方法。在概述从XML Schema创建JSON Schema的方法的同时，本文还演示了JAXB实现的使用（与JDK 9捆绑在一起的xjc版本2.2.12-b150331.1824 [build 1.9.0-ea-b68]）和JSON / Java绑定实现的说明（杰克逊 2.5.4）。

从XSD生成JSON模式的这种方法的步骤可以概括为：

应用JAXB的xjc编译器从XML Schema（XSD）生成Java类。
应用Jackson来从JAXB生成的Java类生成JSON模式。

使用JAXB的xjc从XSD生成Java类

为了便于讨论，我将使用我先前的博客文章A JAXB Nuance：字符串与枚举受限XSD字符串中的枚举使用的简单Food.xsd 。为了方便起见，我在此处重现了该简单模式，但没有特定于先前博客文章的XML注释：

Food.xsd

<?xml version="1.0" encoding="utf-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"xmlns:dustin="http://marxsoftware.blogspot.com/foodxml"targetNamespace="http://marxsoftware.blogspot.com/foodxml"elementFormDefault="qualified"attributeFormDefault="unqualified"><xs:element name="Food"><xs:complexType><xs:sequence><xs:element name="Vegetable" type="dustin:Vegetable" /><xs:element ref="dustin:Fruit" /><xs:element name="Dessert" type="dustin:Dessert" /></xs:sequence></xs:complexType></xs:element><xs:simpleType name="Vegetable"><xs:restriction base="xs:string"><xs:enumeration value="Carrot"/><xs:enumeration value="Squash"/><xs:enumeration value="Spinach"/><xs:enumeration value="Celery"/></xs:restriction></xs:simpleType><xs:element name="Fruit"><xs:simpleType><xs:restriction base="xs:string"><xs:enumeration value="Watermelon"/><xs:enumeration value="Apple"/><xs:enumeration value="Orange"/><xs:enumeration value="Grape"/></xs:restriction></xs:simpleType></xs:element><xs:simpleType name="Dessert"><xs:restriction base="xs:string"><xs:enumeration value="Pie"/><xs:enumeration value="Cake"/><xs:enumeration value="Ice Cream"/></xs:restriction></xs:simpleType></xs:schema>

使用由JDK提供的JAXB实现提供的xjc命令行工具来生成与此XSD相对应的Java类很容易。下一个屏幕快照使用以下命令显示了此过程：

xjc -d jaxb。\ Food.xsd

这个简单的命令生成与提供的Food.xsd相对应的Java类，并将这些类放置在指定的“ jaxb”子目录中。

用Jackson从JAXB生成的类生成JSON

使用现在可用的JAXB生成的类，可以将Jackson应用于这些类以从Java类生成JSON。 Jackson的主门户网站页面上将其描述为“一个用于处理的多功能Java库”，“其灵感来自可用于Java平台的XML工具的质量和种类。” Jackson的存在以及类似的框架和库似乎是Oracle从Java SE 9中删除 JEP 198 （“轻型JSON API”）的原因之一。 [值得注意的是， Java EE 7已经通过其JSR 353 （“与JSON处理有关的Java API”）的实现实现了内置的JSON支持，而该JSR 353与JEP 198无关。）

将Jackson应用于从我们的JAXB生成的Java类生成JSON的第一步之一就是获取并配置Jackson的ObjectMapper类的实例。下一个代码清单显示了实现此目的的一种方法。

获取和配置用于JAXB序列化/反序列化的Jackson ObjectMapper

/*** Create instance of ObjectMapper with JAXB introspector* and default type factory.** @return Instance of ObjectMapper with JAXB introspector*    and default type factory.*/
private ObjectMapper createJaxbObjectMapper()
{final ObjectMapper mapper = new ObjectMapper();final TypeFactory typeFactory = TypeFactory.defaultInstance();final AnnotationIntrospector introspector = new JaxbAnnotationIntrospector(typeFactory);// make deserializer use JAXB annotations (only)mapper.getDeserializationConfig().with(introspector);// make serializer use JAXB annotations (only)mapper.getSerializationConfig().with(introspector);return mapper;
}

上面的代码清单演示了如何获取Jackson的ObjectMapper实例并将其配置为使用默认类型的工厂和面向JAXB的注释自检器。

实例化并适当配置了Jackson的ObjectMapper ，就很容易使用该ObjectMapper实例从生成的JAXB类生成JSON。下一个代码清单中演示了使用不推荐使用的Jackson类JsonSchema实现此目的的一种方法。

使用不推荐使用的com.fasterxml.jackson.databind.jsonschema.JsonSchema类从Java类生成JSON

/*** Write JSON Schema to standard output based upon Java source* code in class whose fully qualified package and class name* have been provided.** @param mapper Instance of ObjectMapper from which to*     invoke JSON schema generation.* @param fullyQualifiedClassName Name of Java class upon*    which JSON Schema will be extracted.*/
private void writeToStandardOutputWithDeprecatedJsonSchema(final ObjectMapper mapper, final String fullyQualifiedClassName)
{try{final JsonSchema jsonSchema = mapper.generateJsonSchema(Class.forName(fullyQualifiedClassName));out.println(jsonSchema);}catch (ClassNotFoundException cnfEx){err.println("Unable to find class " + fullyQualifiedClassName);}catch (JsonMappingException jsonEx){err.println("Unable to map JSON: " + jsonEx);}
}

上面清单中的代码实例化获取提供的Java类的类定义（在我的示例中由JAXB xjc编译器生成的最高级别的Food类），并将对该JAXB生成的类的引用传递给ObjectMapper的generateJsonSchema（Class < ？>）方法。不推荐使用的JsonSchema类的toString（）实现非常有用，并且可以轻松写出从JAXB生成的类生成的JSON。

为了进行演示，我将演示驱动程序作为main（String []）函数提供。在下一个代码清单中提供了该函数和到目前为止的整个类（包括上面显示的方法）。

JsonGenerationFromJaxbClasses.java，版本1

package dustin.examples.jackson;import com.fasterxml.jackson.databind.AnnotationIntrospector;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.type.TypeFactory;
import com.fasterxml.jackson.module.jaxb.JaxbAnnotationIntrospector;import com.fasterxml.jackson.databind.jsonschema.JsonSchema;import static java.lang.System.out;
import static java.lang.System.err;/*** Generates JavaScript Object Notation (JSON) from Java classes* with Java API for XML Binding (JAXB) annotations.*/
public class JsonGenerationFromJaxbClasses
{/*** Create instance of ObjectMapper with JAXB introspector* and default type factory.** @return Instance of ObjectMapper with JAXB introspector*    and default type factory.*/private ObjectMapper createJaxbObjectMapper(){final ObjectMapper mapper = new ObjectMapper();final TypeFactory typeFactory = TypeFactory.defaultInstance();final AnnotationIntrospector introspector = new JaxbAnnotationIntrospector(typeFactory);// make deserializer use JAXB annotations (only)mapper.getDeserializationConfig().with(introspector);// make serializer use JAXB annotations (only)mapper.getSerializationConfig().with(introspector);return mapper;}/*** Write out JSON Schema based upon Java source code in* class whose fully qualified package and class name have* been provided.** @param mapper Instance of ObjectMapper from which to*     invoke JSON schema generation.* @param fullyQualifiedClassName Name of Java class upon*    which JSON Schema will be extracted.*/private void writeToStandardOutputWithDeprecatedJsonSchema(final ObjectMapper mapper, final String fullyQualifiedClassName){try{final JsonSchema jsonSchema = mapper.generateJsonSchema(Class.forName(fullyQualifiedClassName));out.println(jsonSchema);}catch (ClassNotFoundException cnfEx){err.println("Unable to find class " + fullyQualifiedClassName);}catch (JsonMappingException jsonEx){err.println("Unable to map JSON: " + jsonEx);}}/*** Accepts the fully qualified (full package) name of a* Java class with JAXB annotations that will be used to* generate a JSON schema.** @param arguments One argument expected: fully qualified*     package and class name of Java class with JAXB*     annotations.*/public static void main(final String[] arguments){if (arguments.length < 1){err.println("Need to provide the fully qualified name of the highest-level Java class with JAXB annotations.");System.exit(-1);}final JsonGenerationFromJaxbClasses instance = new JsonGenerationFromJaxbClasses();final String fullyQualifiedClassName = arguments[0];final ObjectMapper objectMapper = instance.createJaxbObjectMapper();instance.writeToStandardOutputWithDeprecatedJsonSchema(objectMapper, fullyQualifiedClassName);}
}

要针对基于Food.xsd的JAXB xjc生成的Java类运行此相对通用的代码，我需要提供最高级别生成的类的标准包名称和类名称。在这种情况下，这就是com.blogspot.marxsoftware.foodxml.Food （程序包名称基于XSD的名称空间，因为我在运行xjc时未明确覆盖该名称空间）。当我使用完全限定的类名以及类路径上的JAXB类和Jackson库运行上述代码时，我看到以下JSON写入标准输出。

生成的JSON

{"type":"object","properties":{"vegetable":{"type":"string","enum":["CARROT","SQUASH","SPINACH","CELERY"]},"fruit":{"type":"string"},"dessert":{"type":"string","enum":["PIE","CAKE","ICE_CREAM"]}}}

人类（包括许多开发人员）比打印的JSON更喜欢漂亮的打印。我们可以调整演示类的方法writeToStandardOutputWithDeprecatedJsonSchema(ObjectMapper, String) ，如下所示，以写出缩进的JSON ，以更好地反映其层次结构性质。接下来显示此修改的方法。

修改了writeToStandardOutputWithDeprecatedJsonSchema（ObjectMapper，String）以写入缩进的JSON

/*** Write out indented JSON Schema based upon Java source* code in class whose fully qualified package and class* name have been provided.** @param mapper Instance of ObjectMapper from which to*     invoke JSON schema generation.* @param fullyQualifiedClassName Name of Java class upon*    which JSON Schema will be extracted.*/
private void writeToStandardOutputWithDeprecatedJsonSchema(final ObjectMapper mapper, final String fullyQualifiedClassName)
{try{final JsonSchema jsonSchema = mapper.generateJsonSchema(Class.forName(fullyQualifiedClassName));out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(jsonSchema));}catch (ClassNotFoundException cnfEx){err.println("Unable to find class " + fullyQualifiedClassName);}catch (JsonMappingException jsonEx){err.println("Unable to map JSON: " + jsonEx);}catch (JsonProcessingException jsonEx){err.println("Unable to process JSON: " + jsonEx);}
}

当我使用此修改后的方法再次运行演示类时，JSON输出在美学上更加令人愉悦：

生成带有缩进通信层次结构的JSON

{"type" : "object","properties" : {"vegetable" : {"type" : "string","enum" : [ "CARROT", "SQUASH", "SPINACH", "CELERY" ]},"fruit" : {"type" : "string"},"dessert" : {"type" : "string","enum" : [ "PIE", "CAKE", "ICE_CREAM" ]}}
}

我在这篇文章中一直在使用Jackson 2.5.4。 com.fasterxml.jackson. databind .jsonschema.JsonSchema类com.fasterxml.jackson. databind .jsonschema.JsonSchema 该版本不推荐使用com.fasterxml.jackson. databind .jsonschema.JsonSchema ，并带有以下注释：“从2.2开始，我们建议使用外部JSON Schema生成器模块。” 鉴于此，我现在看一下使用新的首选方法（ Jackson JSON Schema Module方法）。

最显著的变化是使用JsonSchema在类com.fasterxml.jackson.module.jsonSchema包，而不是使用JsonSchema在类com.fasterxml.jackson.databind.jsonschema包。获取这些不同版本的JsonSchema类的实例的方法也不同。下一个代码清单演示了如何使用更新的首选方法从Java类生成JSON。

使用Jackson的更新和首选com.fasterxml.jackson.module.jsonSchema.JsonSchema

/*** Write out JSON Schema based upon Java source code in* class whose fully qualified package and class name have* been provided. This method uses the newer module JsonSchema* class that replaces the deprecated databind JsonSchema.** @param fullyQualifiedClassName Name of Java class upon*    which JSON Schema will be extracted.*/
private void writeToStandardOutputWithModuleJsonSchema(final String fullyQualifiedClassName)
{final SchemaFactoryWrapper visitor = new SchemaFactoryWrapper();final ObjectMapper mapper = new ObjectMapper();try{mapper.acceptJsonFormatVisitor(mapper.constructType(Class.forName(fullyQualifiedClassName)), visitor);final com.fasterxml.jackson.module.jsonSchema.JsonSchema jsonSchema = visitor.finalSchema();out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(jsonSchema));}catch (ClassNotFoundException cnfEx){err.println("Unable to find class " + fullyQualifiedClassName);}catch (JsonMappingException jsonEx){err.println("Unable to map JSON: " + jsonEx);}catch (JsonProcessingException jsonEx){err.println("Unable to process JSON: " + jsonEx);}
}

下表将两个Jackson JsonSchema类的用法与左侧较早显示的已弃用方法（为进行比较而进行了一些调整）并在右侧推荐了较新的方法进行了比较。两者针对要从其编写JSON的相同给定Java类生成相同的输出。

/*** Write out JSON Schema based upon Java source code in* class whose fully qualified package and class name have* been provided. This method uses the deprecated JsonSchema* class in the "databind.jsonschema" package* {@see com.fasterxml.jackson.databind.jsonschema}.** @param fullyQualifiedClassName Name of Java class upon*    which JSON Schema will be extracted.*/
private void writeToStandardOutputWithDeprecatedDatabindJsonSchema(final String fullyQualifiedClassName)
{final ObjectMapper mapper = new ObjectMapper();try{final com.fasterxml.jackson.databind.jsonschema.JsonSchema jsonSchema =mapper.generateJsonSchema(Class.forName(fullyQualifiedClassName));out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(jsonSchema));}catch (ClassNotFoundException cnfEx){err.println("Unable to find class " + fullyQualifiedClassName);}catch (JsonMappingException jsonEx){err.println("Unable to map JSON: " + jsonEx);}catch (JsonProcessingException jsonEx){err.println("Unable to process JSON: " + jsonEx);}
}

/*** Write out JSON Schema based upon Java source code in* class whose fully qualified package and class name have* been provided. This method uses the newer module JsonSchema* class that replaces the deprecated databind JsonSchema.** @param fullyQualifiedClassName Name of Java class upon*    which JSON Schema will be extracted.*/
private void writeToStandardOutputWithModuleJsonSchema(final String fullyQualifiedClassName)
{final SchemaFactoryWrapper visitor = new SchemaFactoryWrapper();final ObjectMapper mapper = new ObjectMapper();try{mapper.acceptJsonFormatVisitor(mapper.constructType(Class.forName(fullyQualifiedClassName)), visitor);final com.fasterxml.jackson.module.jsonSchema.JsonSchema jsonSchema = visitor.finalSchema();out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(jsonSchema));}catch (ClassNotFoundException cnfEx){err.println("Unable to find class " + fullyQualifiedClassName);}catch (JsonMappingException jsonEx){err.println("Unable to map JSON: " + jsonEx);}catch (JsonProcessingException jsonEx){err.println("Unable to process JSON: " + jsonEx);}
}

这篇博客文章展示了两种方法，这些方法使用由Jackson提供的名称为JsonSchema的类的不同版本来基于从具有JAXB的xjc的XSD生成的Java类编写JSON。本文中演示的整个过程是一种从XML Schema生成JSON Schema的方法。

翻译自: https://www.javacodegeeks.com/2015/06/generating-json-schema-from-xsd-with-jaxb-and-jackson.html

jaxb xsd生成xml