讲代码生成器之前先要说说模板，什么叫模板呢，举个例子吧，汇款单都见过吧，你不填写的那些内容都属于模板范畴
说到这应该明白了吧，模板就是把共性提取出来反复使用，节约时间、工作量。。。。。
那跟代码生成器有什么关系呢，思考一下在编程语言中所有的语言是不是都用共性或者说规范，这些都是固定不变的，在具体点，软件行业也是分主营业务 的，比如OA、CRM、ERP、SCM等等，那么各个业务方向的软件是不是也有其行业特点，这是不是也是固定的，那么这就完了，这些独特的地方是不是可以 提取出来作为模板呢，不言而喻
言归正传，说到模板就不得不说现在主流的模板技术了，FreeMarker、Velocity(这个google在用)，模板技术推崇一种模式：
输出=模板+数据，所以运用到代码生成器上也是一样的道理，举个简单例子比如要生成一个javabean组件，就普通的pojo类，
那么先分析一下生成这种类有什么共性呢，关键字就不用说了，getter和setter方法都是get+属性名uppercase首字母和set+ 属性名uppercase首字母，还有“{}”、“;”、“()”等等这些都是不变的，那么这些内容就可以作为模板内容，包名、类名、属性名这些是人为要 取的，这些是变化的，故变的这部分就作为数据，这样就可以根据不同的‘数据’来生成不同的javabean
项目准备：先去down个freemarker.jar包， http://freemarker.org/freemarkerdownload.html
上篇讨论了代码生成器的原理，输出=模板+数据，那么现在就生成一个Student.java文件做个简单例子。
首先先写出模板，先解决一个问题，上篇有讲到属性名首字母大写的问题
由于freemarker中不支持将首字母大写(属性名中用到)，那么自己先写一个自定义宏如下：
源码 打印 ？ package com; import java.io.IOException; import java.io.Writer; import java.util.Map; import freemarker.core.Environment; import freemarker.template.TemplateDirectiveBody; import freemarker.template.TemplateDirectiveModel; import freemarker.template.TemplateException; import freemarker.template.TemplateModel; import freemarker.template.TemplateModelException; public class UpperFirstCharacter implements TemplateDirectiveModel { public void execute(Environment env, Map params, TemplateModel[] loopVars, TemplateDirectiveBody body) throws TemplateException, IOException { // Check if no parameters were given: if (!params.isEmpty()) { throw new TemplateModelException( "This directive doesn't allow parameters." ); } if (loopVars.length != 0 ) { throw new TemplateModelException( "This directive doesn't allow loop variables." ); } // If there is non-empty nested content: if (body != null ) { // Executes the nested body. Same as <#nested> in FTL, except // that we use our own writer instead of the current output writer. body.render(new UpperCaseFilterWriter(env.getOut())); } else { throw new RuntimeException( "missing body" ); } } /** * A {@link Writer} that transforms the character stream to upper case * and forwards it to another {@link Writer}. */ private static class UpperCaseFilterWriter extends Writer { private final Writer out; UpperCaseFilterWriter (Writer out) { this .out = out; } public void write( char [] cbuf, int off, int len) throws IOException { // char[] transformedCbuf = new char[len]; // for (int i = 0; i < len; i++) { // transformedCbuf[i] = Character.toUpperCase(cbuf[i + off]); // } // out.write(transformedCbuf); cbuf[0 ] = Character.toUpperCase(cbuf[ 0 ]); out.write(String.valueOf(cbuf).trim());///把右边空格去掉 } public void flush() throws IOException { out.flush(); } public void close() throws IOException { out.close(); } } } package com; import java.io.IOException; import java.io.Writer; import java.util.Map; import freemarker.core.Environment; import freemarker.template.TemplateDirectiveBody; import freemarker.template.TemplateDirectiveModel; import freemarker.template.TemplateException; import freemarker.template.TemplateModel; import freemarker.template.TemplateModelException; public class UpperFirstCharacter implements TemplateDirectiveModel { public void execute(Environment env, Map params, TemplateModel[] loopVars, TemplateDirectiveBody body) throws TemplateException, IOException { // Check if no parameters were given: if (!params.isEmpty()) { throw new TemplateModelException( "This directive doesn't allow parameters."); } if (loopVars.length != 0) { throw new TemplateModelException( "This directive doesn't allow loop variables."); } // If there is non-empty nested content: if (body != null) { // Executes the nested body. Same as <#nested> in FTL, except // that we use our own writer instead of the current output writer. body.render(new UpperCaseFilterWriter(env.getOut())); } else { throw new RuntimeException("missing body"); } } /** * A {@link Writer} that transforms the character stream to upper case * and forwards it to another {@link Writer}. */ private static class UpperCaseFilterWriter extends Writer { private final Writer out; UpperCaseFilterWriter (Writer out) { this.out = out; } public void write(char[] cbuf, int off, int len) throws IOException { // char[] transformedCbuf = new char[len]; // for (int i = 0; i < len; i++) { // transformedCbuf[i] = Character.toUpperCase(cbuf[i + off]); // } // out.write(transformedCbuf); cbuf[0] = Character.toUpperCase(cbuf[0]); out.write(String.valueOf(cbuf).trim());///把右边空格去掉 } public void flush() throws IOException { out.flush(); } public void close() throws IOException { out.close(); } } }
下面呢就可以编写模板了，代码如下：
源码 打印 ？ package ${ package }; //这个地方可以事先定义好需要的类 import java.util.Date; import java.io.Serializable; public class ${className} implements Serializable{ <#list properties as pro> private ${pro.proType} ${pro.proName}; </#list> <#list properties as pro> public void set< @upperFC >${pro.proName}</ @upperFC >(${pro.proType} ${pro.proName}){ this .${pro.proName}=${pro.proName}; } public ${pro.proType} get< @upperFC >${pro.proName}</ @upperFC >(){ return this .${pro.proName}; } </#list> } package ${package}; //这个地方可以事先定义好需要的类 import java.util.Date; import java.io.Serializable; public class ${className} implements Serializable{ <#list properties as pro> private ${pro.proType} ${pro.proName}; </#list> <#list properties as pro> public void set<@upperFC>${pro.proName}</@upperFC>(${pro.proType} ${pro.proName}){ this.${pro.proName}=${pro.proName}; } public ${pro.proType} get<@upperFC>${pro.proName}</@upperFC>(){ return this.${pro.proName}; } </#list> }模板文件取名为javabean.html，在com包下
下面编写测试类：
源码 打印 ？ package com; import java.io.File; import java.io.FileOutputStream; import java.io.IOException; import java.io.OutputStreamWriter; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; import freemarker.template.Configuration; import freemarker.template.Template; import freemarker.template.TemplateException; public class Test { /** * @param args */ public static void main(String[] args) { //System.out.println(System.getProperty("user.dir")+"============"); Configuration cfg = new Configuration(); try { cfg.setClassForTemplateLoading(Test.class , "/com" ); //指定模板所在的classpath目录 cfg.setSharedVariable("upperFC" , new UpperFirstCharacter()); //添加一个"宏"共享变量用来将属性名首字母大写 Template t = cfg.getTemplate("javabean.html" ); //指定模板 FileOutputStream fos = new FileOutputStream( new File( "d:/Student.java" )); //java文件的生成目录 //模拟数据源 Map data = new HashMap(); data.put("package" , "edu" ); //包名 data.put("className" , "Student" ); List pros = new ArrayList(); Map pro_1 = new HashMap(); pro_1.put("proType" , String. class .getSimpleName()); pro_1.put("proName" , "name" ); pros.add(pro_1); Map pro_2 = new HashMap(); pro_2.put("proType" , String. class .getSimpleName()); pro_2.put("proName" , "sex" ); pros.add(pro_2); Map pro_3 = new HashMap(); pro_3.put("proType" , Integer. class .getSimpleName()); pro_3.put("proName" , "age" ); pros.add(pro_3); data.put("properties" , pros); t.process(data, new OutputStreamWriter(fos, "utf-8" )); // fos.flush(); fos.close(); } catch (IOException e) { e.printStackTrace(); } catch (TemplateException e) { e.printStackTrace(); } } } package com; import java.io.File; import java.io.FileOutputStream; import java.io.IOException; import java.io.OutputStreamWriter; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; import freemarker.template.Configuration; import freemarker.template.Template; import freemarker.template.TemplateException; public class Test { /** * @param args */ public static void main(String[] args) { //System.out.println(System.getProperty("user.dir")+"============"); Configuration cfg = new Configuration(); try { cfg.setClassForTemplateLoading(Test.class, "/com");//指定模板所在的classpath目录 cfg.setSharedVariable("upperFC", new UpperFirstCharacter());//添加一个"宏"共享变量用来将属性名首字母大写 Template t = cfg.getTemplate("javabean.html");//指定模板 FileOutputStream fos = new FileOutputStream(new File("d:/Student.java"));//java文件的生成目录 //模拟数据源 Map data = new HashMap(); data.put("package", "edu");//包名 data.put("className", "Student"); List pros = new ArrayList(); Map pro_1 = new HashMap(); pro_1.put("proType", String.class.getSimpleName()); pro_1.put("proName", "name"); pros.add(pro_1); Map pro_2 = new HashMap(); pro_2.put("proType", String.class.getSimpleName()); pro_2.put("proName", "sex"); pros.add(pro_2); Map pro_3 = new HashMap(); pro_3.put("proType", Integer.class.getSimpleName()); pro_3.put("proName", "age"); pros.add(pro_3); data.put("properties", pros); t.process(data, new OutputStreamWriter(fos,"utf-8"));// fos.flush(); fos.close(); } catch (IOException e) { e.printStackTrace(); } catch (TemplateException e) { e.printStackTrace(); } } }
运行一下测试类，在D盘可以找到一个Student.java的文件，打开看看对不对
