如果你并不打算使用类继承结构并不是很有必要阅读本文。请先阅读我写的另一篇文章 "使用hibernate扩展工具Hbm2JavaTask根据配置文件生成持久化对象类(2.1.2)"1.在文档第8章(hibernate/doc/reference/zh-cn/html/inheritance.html)有提到
“每个子类一个表”的映射是这样的：
<class name="Payment" table="PAYMENT"> <id name="id" type="long" column="PAYMENT_ID"> <generator class="native"/> </id> <property name="amount" column="AMOUNT"/> ... <joined-subclass name="CreditCardPayment" table="CREDIT_PAYMENT"> <key column="PAYMENT_ID"/> ... </joined-subclass> <joined-subclass name="CashPayment" table="CASH_PAYMENT"> <key column="PAYMENT_ID"/> ... </joined-subclass> <joined-subclass name="ChequePayment" table="CHEQUE_PAYMENT"> <key column="PAYMENT_ID"/> ... </joined-subclass></class>
2.文档第5章(hibernate/doc/reference/zh-cn/html/mapping.html)有提到
允许在独立的映射文档中定义subclass和joined-subclass，直接位于hibernate-mapping下。这就可以让你每次扩展你的类层次的时候，加入新的映射文件就行了。在子类的映射中你必须指定一个extents属性，指明先前已经映射过的超类。使用这个功能的时候，一定要注意映射文件的排序是非常重要的！
<hibernate-mapping> <subclass name="eg.subclass.DomesticCat" extends="eg.Cat" discriminator-value="D"> <property name="name" type="string"/> </subclass></hibernate-mapping>
3.根据以上两点，偶根据第8章的PAYMENT创建了一个工程，把joined-subclass移了出来，现在工程目录结构如下 Payment <dir>|-src <dir>|-hbm <dir> |-payment <dir> |-Payment.hbm.xml |-CreditCardPayment.hbm.xml |-CashPayment.hbm.xml|-classes <dir>|-lib <dir>|-build.xml|-hibernate.codegen.xml|-log4j.properties4. 本文不再重复build.xml, hibernate.codegen.xml, log4j.properties三个文件的内容。可在"使用hibernate扩展工具Hbm2JavaTask根据配置文件生成持久化对象类(2.1.2)"一文查看这三个文件的内容。此处仅列出.hbm.xml文件内容。 4.1 Payment.hbm.xml<?xml version="1.0" encoding="gbk"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN" "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd"><hibernate-mapping> <class name="payment.Payment" table="PAYMENT"> <id name="id" type="long" column="PAYMENT_ID"> <generator class="native"/> </id> <property name="amount" column="AMOUNT" type="long"/> </class></hibernate-mapping> 4.2 CreditCardPayment.hbm.xml
<?xml version="1.0" encoding="gbk"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN" "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd"><hibernate-mapping><joined-subclass name="payment.CreditCardPayment" table="CREDIT_PAYMENT" extends="payment.Payment"> <key column="PAYMENT_ID"/></joined-subclass></hibernate-mapping>
4.3 CashPayment.hbm.xml
<?xml version="1.0" encoding="gbk"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN" "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd"><hibernate-mapping><joined-subclass name="payment.CashPayment" table="CASH_PAYMENT" extends="payment.Payment"> <key column="PAYMENT_ID"/></joined-subclass></hibernate-mapping>
5.在命令行进入工程目录，运行ant，发生错误，关键提示如下： net.sf.hibernate.MappingException: Cannot extend unmapped class payment.Payment6.查错过程我就不说了，比较无聊，只说一下问题出在哪里 6.1 Hbm2JavaTask里对配置文件列表做了循环，每个文件单独处理，所以有关联的类就找不到了。 6.2 但是CodeGenerator类也有不妥，没有考虑文件排列问题，因为子类可能先于父类被处理。7.下面帖出两个修改过的文件代码。在修改的地方加了中文注释。 7.1 net.sf.hibernate.tool.hbm2java.Hbm2JavaTask
package net.sf.hibernate.tool.hbm2java;import java.io.File;import java.io.PrintWriter;import java.io.StringWriter;import java.util.ArrayList;import java.util.List;import org.apache.tools.ant.BuildException;import org.apache.tools.ant.DirectoryScanner;import org.apache.tools.ant.Task;import org.apache.tools.ant.types.FileSet;import org.apache.tools.ant.types.Path;import org.apache.tools.ant.types.Reference;import org.apache.commons.logging.Log;import org.apache.commons.logging.LogFactory;/** * Task for hbm2java (Hibernates codegenerator) * * * @author GBegley and max * */public class Hbm2JavaTask extends Task { private static final Log log = LogFactory.getLog(CodeGenerator.class); private File configurationFile; private Path compileClasspath; private File outputDir; private List filesets = new ArrayList(); /** * Set a hbm2java <literal>config.xml</literal> configuration file * @param the file name */ public void setConfig(File configurationFile) { this.configurationFile = configurationFile; } /** * Set the classpath to be used for this compilation. * * @param classpath an Ant Path object containing the compilation classpath. */ public void setClasspath(Path classpath) { if (compileClasspath == null) { compileClasspath = classpath; } else { compileClasspath.append(classpath); } } /** Gets the classpath to be used for this compilation. */ public Path getClasspath() { return compileClasspath; } /** * Adds a path to the classpath. */ public Path createClasspath() { if (compileClasspath == null) { compileClasspath = new Path(getProject()); } return compileClasspath.createPath(); } /** * Adds a reference to a classpath defined elsewhere. */ public void setClasspathRef(Reference r) { createClasspath().setRefid(r); } /** * Adds a set of files to translate. */ public void addFileset(FileSet set) { filesets.add(set); } /** * Sets the output directory. * * @param binDirectory directory */ public void setOutput(File outDirectory) { this.outputDir = outDirectory; } public void execute() throws BuildException { List fileList = getTargetFiles(); if (fileList.size() == 0) return; log("Processing " + fileList.size() + " files."); try { log("Building hibernate objects"); //这个循环是错误1， //for (int i = 0; i < fileList.size(); i++) { // processFile(outputDir, (File) fileList.get(i)); //} //要修改processFile方法 processFile(outputDir, fileList); } catch (Throwable t) { StringWriter sw = new StringWriter(); t.printStackTrace(new PrintWriter(sw)); throw new BuildException("Caused by:\n" + sw.toString()); } } /** * * * Comment: * The initial ant task had some initial filtering on the hbm.xml/java names to only process the needed files. * That is not possible to decide in the ant task without implementing the same logic present in hbm2java. * Thus I've removed it and let it be something that hbm2java should do. * * * @return */ private List getTargetFiles() { List l = new java.util.ArrayList(); // deal with the filesets for (int i = 0; i < filesets.size(); i++) { FileSet fs = (FileSet) filesets.get(i); File parent = fs.getDir( getProject() ); DirectoryScanner ds = fs.getDirectoryScanner(getProject()); String[] files = ds.getIncludedFiles(); for (int j = 0; j < files.length; j++) { File srcFile = new File( parent, files[j] ); l.add( srcFile ); } } return l; } //修改了方法参数 private void processFile(File outputDir, List fileList) { List args = new ArrayList(); if (outputDir != null) { args.add("--output=" + outputDir.getAbsolutePath()); } if (configurationFile != null) { args.add("--config=" + configurationFile); } // 把所有文件都加入命令行参数 for ( int i = 0; i < fileList.size(); i++ ){ args.add(((File)fileList.get(i)).getAbsolutePath()); } try { net.sf.hibernate.tool.hbm2java.CodeGenerator.main((String[]) args.toArray(new String[args.size()])); } catch (Throwable t) { StringWriter sw = new StringWriter(); t.printStackTrace(new PrintWriter(sw)); throw new BuildException("Caused by:\n" + sw.toString()); } }}
7.2 net.sf.hibernate.tool.hbm2java.CodeGenerator
/* * $Id: CodeGenerator.java,v 1.7 2004/03/22 20:41:47 maxcsaucdk Exp $ */package net.sf.hibernate.tool.hbm2java;import java.io.File;import java.util.ArrayList;import java.util.HashMap;import java.util.Iterator;import java.util.List;import net.sf.hibernate.MappingException;import net.sf.hibernate.util.DTDEntityResolver;import org.apache.commons.collections.MultiHashMap;import org.apache.commons.collections.MultiMap;import org.apache.commons.logging.Log;import org.apache.commons.logging.LogFactory;import org.jdom.Document;import org.jdom.Element;import org.jdom.input.SAXBuilder;import org.xml.sax.ErrorHandler;import org.xml.sax.SAXParseException;/** * */public class CodeGenerator { private static final Log log = LogFactory.getLog(CodeGenerator.class); public static void main(String[] args) { if(args.length==0) { System.err.println("No arguments provided. Nothing to do. Exit."); System.exit(-1); } try { ArrayList mappingFiles = new ArrayList(); SAXBuilder builder = new SAXBuilder(true); builder.setEntityResolver( new DTDEntityResolver() ); builder.setErrorHandler( new ErrorHandler() { public void error(SAXParseException error) { log.error("Error parsing XML: " + error.getSystemId() + '(' + error.getLineNumber() + ')',error); } public void fatalError(SAXParseException error) { error(error); } public void warning(SAXParseException error) { log.warn("Warning parsing XML: " + error.getSystemId() + '(' + error.getLineNumber() + ')' ); } } ); String outputDir = null; List generators = new ArrayList(); MultiMap globalMetas = new MultiHashMap(); // parse command line parameters for (int i = 0; i < args.length; i++) { if (args[i].startsWith("--")) { if ( args[i].startsWith("--config=") ) { // parse config xml file builder.setValidation(false); Document document = builder.build( new File( args[i].substring(9) ) ); globalMetas = MetaAttributeHelper.loadAndMergeMetaMap(document.getRootElement(), null); Iterator generateElements = document.getRootElement().getChildren("generate").iterator(); while (generateElements.hasNext()) { generators.add( new Generator( (Element) generateElements.next() ) ); } builder.setValidation(true); } else if ( args[i].startsWith("--output=") ) { outputDir = args[i].substring(9); } } else { mappingFiles.add( args[i] ); } } // if no config xml file, add a default generator if (generators.size() == 0) { generators.add( new Generator() ); } HashMap classMappings = new HashMap(); builder.setValidation(true); // 这个循环是错误2 // 改成只处理class映射 for ( Iterator iter = mappingFiles.iterator(); iter.hasNext(); ) { // parse the mapping file File file = new File( (String) iter.next() ); log.debug(file.getAbsolutePath()); Document document = builder.build( file); Element rootElement = document.getRootElement(); org.jdom.Attribute a = rootElement.getAttribute("package"); String pkg = null; if(a!=null) { pkg = a.getValue(); } MappingElement me = new MappingElement(rootElement, null/**TODO-hbm2java: - should be config.xml**/); Iterator classElements = rootElement.getChildren("class").iterator(); MultiMap mm = MetaAttributeHelper.loadAndMergeMetaMap(rootElement, globalMetas); handleClass(pkg,me, classMappings, classElements, mm, false); } // 复制了上一个循环 // 处理subclass和joined-class映射 for ( Iterator iter = mappingFiles.iterator(); iter.hasNext(); ) { // parse the mapping file File file = new File( (String) iter.next() ); Document document = builder.build( file); Element rootElement = document.getRootElement(); org.jdom.Attribute a = rootElement.getAttribute("package"); String pkg = null; if(a!=null) { pkg = a.getValue(); } MappingElement me = new MappingElement(rootElement, null/**TODO-hbm2java: - should be config.xml**/); MultiMap mm = MetaAttributeHelper.loadAndMergeMetaMap(rootElement, globalMetas); Iterator classElements = rootElement.getChildren("subclass").iterator(); handleClass(pkg,me,classMappings, classElements, mm, true); classElements = rootElement.getChildren("joined-subclass").iterator(); handleClass(pkg,me,classMappings, classElements, mm, true); } // generate source files for ( Iterator iterator = generators.iterator(); iterator.hasNext(); ) { Generator g = (Generator) iterator.next(); g.setBaseDirName(outputDir); g.generate(classMappings); } } catch (Exception e) { e.printStackTrace(); } } private static void handleClass(String classPackage, MappingElement me, HashMap classMappings, Iterator classElements, MultiMap mm, boolean extendz) throws MappingException { while ( classElements.hasNext() ) { Element clazz = (Element) classElements.next(); if(!extendz) { ClassMapping cmap = new ClassMapping(classPackage, clazz, me, mm); classMappings.put(cmap.getFullyQualifiedName(),cmap); } else { String ex = clazz.getAttributeValue("extends"); if(ex==null) { throw new MappingException("Missing extends attribute on <" + clazz.getName() + " name=" + clazz.getAttributeValue("name") + ">" ); } ClassMapping superclass = (ClassMapping) classMappings.get(ex); if(superclass == null) { throw new MappingException("Cannot extend unmapped class " + ex); } ClassMapping subclassMapping = new ClassMapping(classPackage, me, superclass.getClassName(), superclass, clazz, mm); superclass.addSubClass(subclassMapping); } } }}
