由于JAXB是JDK的一部分，因此它是处理XML文档最常用的框架之一。 它提供了一种从XML文档检索数据并将其存储到Java类的简便方法。 因为几乎每个Java开发人员都已经使用过JAXB，所以我不会解释不同的JAXB批注。 相反，我将专注于一个名为xjc的命令行工具，并向您展示如何基于现有XSD架构描述生成绑定类。

为现有XML接口实现所有绑定类可能是一项耗时且繁琐的任务。 但好消息是，您不需要这样做。 如果您具有XSD架构描述，则可以使用xjc绑定编译器创建所需的类。 甚至更好的是，xjc是JDK的一部分。 因此，不需要外部工具，如果需要，您应该始终准备好使用它。

使用xjc

如下面的代码片段所示，xjc支持许多选项。 最重要的是：

• -d定义生成的类应在文件系统中存储的位置，
• -p定义要使用的软件包，当然
• -帮助，如果您还有其他需要。

Usage: xjc [-options ...] <schema file/URL/dir/jar> ... [-b <bindinfo>] ...
If dir is specified, all schema files in it will be compiled.
If jar is specified, /META-INF/sun-jaxb.episode binding file will be compiled.
Options:-nv                :  do not perform strict validation of the input schema(s)-extension         :  allow vendor extensions - do not strictly follow theCompatibility Rules and App E.2 from the JAXB Spec-b <file/dir>      :  specify external bindings files (each <file> must have its own -b)If a directory is given, **/*.xjb is searched-d <dir>           :  generated files will go into this directory-p <pkg>           :  specifies the target package-httpproxy <proxy> :  set HTTP/HTTPS proxy. Format is [user[:password]@]proxyHost:proxyPort-httpproxyfile <f> :  Works like -httpproxy but takes the argument in a file to protect password-classpath <arg>   :  specify where to find user class files-catalog <file>    :  specify catalog files to resolve external entity referencessupport TR9401, XCatalog, and OASIS XML Catalog format.-readOnly          :  generated files will be in read-only mode-npa               :  suppress generation of package level annotations (**/package-info.java)-no-header         :  suppress generation of a file header with timestamp-target (2.0|2.1)  :  behave like XJC 2.0 or 2.1 and generate code that doesnt use any 2.2 features.-encoding <encoding> :  specify character encoding for generated source files-enableIntrospection :  enable correct generation of Boolean getters/setters to enable Bean Introspection apis-contentForWildcard  :  generates content property for types with multiple xs:any derived elements-xmlschema         :  treat input as W3C XML Schema (default)-relaxng           :  treat input as RELAX NG (experimental,unsupported)-relaxng-compact   :  treat input as RELAX NG compact syntax (experimental,unsupported)-dtd               :  treat input as XML DTD (experimental,unsupported)-wsdl              :  treat input as WSDL and compile schemas inside it (experimental,unsupported)-verbose           :  be extra verbose-quiet             :  suppress compiler output-help              :  display this help message-version           :  display version information-fullversion       :  display full version informationExtensions:-Xinject-code      :  inject specified Java code fragments into the generated code-Xlocator          :  enable source location support for generated code-Xsync-methods     :  generate accessor methods with the 'synchronized' keyword-mark-generated    :  mark the generated code as @javax.annotation.Generated-episode <FILE>    :  generate the episode file for separate compilation

例

好的，让我们看一个例子。 我们将使用以下XSD模式定义和xjc来生成具有描述的属性和必需的JAXB批注的Author和Book类。

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<xs:schema version="1.0" xmlns:xs="http://www.w3.org/2001/XMLSchema"><xs:element name="author" type="author"/><xs:element name="book" type="book"/><xs:complexType name="author"><xs:sequence><xs:element name="firstName" type="xs:string" minOccurs="0"/><xs:element name="lastName" type="xs:string" minOccurs="0"/></xs:sequence></xs:complexType><xs:complexType name="book"><xs:sequence><xs:element ref="author" minOccurs="0"/><xs:element name="pages" type="xs:int"/><xs:element name="publicationDate" type="xs:dateTime" minOccurs="0"/><xs:element name="title" type="xs:string" minOccurs="0"/></xs:sequence></xs:complexType>
</xs:schema>

以下命令调用xjc，并为生成的类，包和XSD模式文件提供目标目录。

xjc -d src -p blog.thoughts.on.java schema.xsdparsing a schema...
compiling a schema...
blog\thoughts\on\java\Author.java
blog\thoughts\on\java\Book.java
blog\thoughts\on\java\ObjectFactory.java

好的，操作成功完成，现在在src目录中有3个生成的类。 这可能比某些人预期的要多。 因此，让我们看看它们中的每一个。

类Author和Book看起来像预期的那样。 它们包含XSD架构中描述的属性和必需的JAXB批注。

//
// This file was generated by the JavaTM Architecture for XML Binding(JAXB) Reference Implementation, v2.2.4-2
// See <a href="http://java.sun.com/xml/jaxb">http://java.sun.com/xml/jaxb</a>
// Any modifications to this file will be lost upon recompilation of the source schema.
// Generated on: 2014.01.13 at 07:38:24 PM CET
//package blog.thoughts.on.java;import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlType;/*** <p>Java class for author complex type.* * <p>The following schema fragment specifies the expected content contained within this class.* * <pre>* <complexType name="author">*   <complexContent>*     <restriction base="{http://www.w3.org/2001/XMLSchema}anyType">*       <sequence>*         <element name="firstName" type="{http://www.w3.org/2001/XMLSchema}string" minOccurs="0"/>*         <element name="lastName" type="{http://www.w3.org/2001/XMLSchema}string" minOccurs="0"/>*       </sequence>*     </restriction>*   </complexContent>* </complexType>* </pre>* * */
@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "author", propOrder = {"firstName","lastName"
})
public class Author {protected String firstName;protected String lastName;/*** Gets the value of the firstName property.* * @return*     possible object is*     {@link String }*     */public String getFirstName() {return firstName;}/*** Sets the value of the firstName property.* * @param value*     allowed object is*     {@link String }*     */public void setFirstName(String value) {this.firstName = value;}/*** Gets the value of the lastName property.* * @return*     possible object is*     {@link String }*     */public String getLastName() {return lastName;}/*** Sets the value of the lastName property.* * @param value*     allowed object is*     {@link String }*     */public void setLastName(String value) {this.lastName = value;}}

//
// This file was generated by the JavaTM Architecture for XML Binding(JAXB) Reference Implementation, v2.2.4-2
// See <a href="http://java.sun.com/xml/jaxb">http://java.sun.com/xml/jaxb</a>
// Any modifications to this file will be lost upon recompilation of the source schema.
// Generated on: 2014.01.13 at 07:38:24 PM CET
//package blog.thoughts.on.java;import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlSchemaType;
import javax.xml.bind.annotation.XmlType;
import javax.xml.datatype.XMLGregorianCalendar;/*** <p>Java class for book complex type.* * <p>The following schema fragment specifies the expected content contained within this class.* * <pre>* <complexType name="book">*   <complexContent>*     <restriction base="{http://www.w3.org/2001/XMLSchema}anyType">*       <sequence>*         <element ref="{}author" minOccurs="0"/>*         <element name="pages" type="{http://www.w3.org/2001/XMLSchema}int"/>*         <element name="publicationDate" type="{http://www.w3.org/2001/XMLSchema}dateTime" minOccurs="0"/>*         <element name="title" type="{http://www.w3.org/2001/XMLSchema}string" minOccurs="0"/>*       </sequence>*     </restriction>*   </complexContent>* </complexType>* </pre>* * */
@XmlAccessorType(XmlAccessType.FIELD)
@XmlType(name = "book", propOrder = {"author","pages","publicationDate","title"
})
public class Book {protected Author author;protected int pages;@XmlSchemaType(name = "dateTime")protected XMLGregorianCalendar publicationDate;protected String title;/*** Gets the value of the author property.* * @return*     possible object is*     {@link Author }*     */public Author getAuthor() {return author;}/*** Sets the value of the author property.* * @param value*     allowed object is*     {@link Author }*     */public void setAuthor(Author value) {this.author = value;}/*** Gets the value of the pages property.* */public int getPages() {return pages;}/*** Sets the value of the pages property.* */public void setPages(int value) {this.pages = value;}/*** Gets the value of the publicationDate property.* * @return*     possible object is*     {@link XMLGregorianCalendar }*     */public XMLGregorianCalendar getPublicationDate() {return publicationDate;}/*** Sets the value of the publicationDate property.* * @param value*     allowed object is*     {@link XMLGregorianCalendar }*     */public void setPublicationDate(XMLGregorianCalendar value) {this.publicationDate = value;}/*** Gets the value of the title property.* * @return*     possible object is*     {@link String }*     */public String getTitle() {return title;}/*** Sets the value of the title property.* * @param value*     allowed object is*     {@link String }*     */public void setTitle(String value) {this.title = value;}}

第三类，也许是意外类，是ObjectFactory类。 它包含每个生成的类或接口的工厂方法。 如果您需要创建对象的JAXBElement表示形式，这将非常有用。

//
// This file was generated by the JavaTM Architecture for XML Binding(JAXB) Reference Implementation, v2.2.4-2
// See <a href="http://java.sun.com/xml/jaxb">http://java.sun.com/xml/jaxb</a>
// Any modifications to this file will be lost upon recompilation of the source schema.
// Generated on: 2014.01.13 at 07:38:24 PM CET
//package blog.thoughts.on.java;import javax.xml.bind.JAXBElement;
import javax.xml.bind.annotation.XmlElementDecl;
import javax.xml.bind.annotation.XmlRegistry;
import javax.xml.namespace.QName;/*** This object contains factory methods for each * Java content interface and Java element interface * generated in the blog.thoughts.on.java package. * <p>An ObjectFactory allows you to programatically * construct new instances of the Java representation * for XML content. The Java representation of XML * content can consist of schema derived interfaces * and classes representing the binding of schema * type definitions, element declarations and model * groups.  Factory methods for each of these are * provided in this class.* */
@XmlRegistry
public class ObjectFactory {private final static QName _Author_QNAME = new QName("", "author");private final static QName _Book_QNAME = new QName("", "book");/*** Create a new ObjectFactory that can be used to create new instances of schema derived classes for package: blog.thoughts.on.java* */public ObjectFactory() {}/*** Create an instance of {@link Author }* */public Author createAuthor() {return new Author();}/*** Create an instance of {@link Book }* */public Book createBook() {return new Book();}/*** Create an instance of {@link JAXBElement }{@code <}{@link Author }{@code >}}* */@XmlElementDecl(namespace = "", name = "author")public JAXBElement<Author> createAuthor(Author value) {return new JAXBElement<Author>(_Author_QNAME, Author.class, null, value);}/*** Create an instance of {@link JAXBElement }{@code <}{@link Book }{@code >}}* */@XmlElementDecl(namespace = "", name = "book")public JAXBElement<Book> createBook(Book value) {return new JAXBElement<Book>(_Book_QNAME, Book.class, null, value);}}

结论

我们研究了xjc并将其用于为现有XSD模式定义生成所需的绑定类。 xjc为每种复杂类型生成一个类，并为简化创建JAXBElement表示形式提供一个附加的工厂类。

您如何看待xjc和生成的代码？ 请给我评论，并告诉我有关的信息。

我认为该工具可生成非常干净的代码并节省大量时间。 在大多数情况下，可以将生成的代码直接添加到项目中。 但是，即使不是这种情况，基于生成的代码进行一些重构比自己做所有事情要快得多。

翻译自: https://www.javacodegeeks.com/2014/05/generate-your-jaxb-classes-in-a-second-with-xjc.html