插入式注解处理器

通过Javac命令的 -processor 参数来执行编译时需要附带的注解处理器，如果有多个注解处理器的话，用逗号分隔。

还可以使用-XprintRounds和-XprintProcessorInfo参数来查看注解处理器运作的详细信息。

NameCheckProcessor的实例只演示了JSR-269嵌入式注解处理API其中的一部分功能，基于这组API支持的项目还有用于效验Hibernate标签使用正确性的Hibernate Validator Annotation Processor（本质上与NameCheckProcessor所做的事情差不多），自动为字段生成getter和setter方法的Project Lombok（根据已有元素生成新的语法树元素）等，

 代码如下：

import java.util.EnumSet;import java.util.Set;import javax.annotation.processing.AbstractProcessor;import javax.annotation.processing.Messager;import javax.annotation.processing.ProcessingEnvironment;import javax.annotation.processing.RoundEnvironment;import javax.annotation.processing.SupportedAnnotationTypes;import javax.annotation.processing.SupportedSourceVersion;import javax.lang.model.SourceVersion;import javax.lang.model.element.Element;import javax.lang.model.element.ElementKind;import javax.lang.model.element.ExecutableElement;import javax.lang.model.element.Name;import javax.lang.model.element.TypeElement;import javax.lang.model.element.VariableElement;import javax.lang.model.util.ElementScanner7;import javax.tools.Diagnostic.Kind;/** * javac NameCheckProcessor.java * javac -processor NameCheckProcessor FT.java * @author kevin * *///使用*表示支持所有的Annotations @SupportedAnnotationTypes(value = "*")@SupportedSourceVersion(value = SourceVersion.RELEASE_7)public class NameCheckProcessor extends AbstractProcessor {@Overridepublic synchronized void init(ProcessingEnvironment processingEnv) {super.init(processingEnv);this.nameCheck = new NameCheck(processingEnv);}private NameCheck nameCheck;@Overridepublic boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {if (!roundEnv.processingOver()) {for (Element element : roundEnv.getRootElements()) {nameCheck.check(element);}}return false;}/** * 程序名称规范的编译器插件 如果程序命名不合规范，将会输出一个编译器的Warning信息 *  * @author kevin *  */public static class NameCheck {Messager messager = null;public NameCheckScanner nameCheckScanner;private NameCheck(ProcessingEnvironment processingEnv) {messager = processingEnv.getMessager();nameCheckScanner = new NameCheckScanner(processingEnv);}/** * 对Java程序明明进行检查，根据《Java语言规范（第3版）》6.8节的要求，Java程序命名应当符合下列格式： * <ul> * <li>类或接口：符合驼式命名法，首字母大写。 * <li>方法：符合驼式命名法，首字母小写。 * <li>字段： * <ul> * <li>类，实例变量：符合驼式命名法，首字母小写。 * <li>常量：要求全部大写 * </ul> * </ul> *  * @param element */public void check(Element element) {nameCheckScanner.scan(element);}/** * 名称检查器实现类，继承了1.6中新提供的ElementScanner6<br> * 将会以Visitor模式访问抽象语法数中得元素 *  * @author kevin *  */public static class NameCheckScanner extends ElementScanner7<Void, Void> {Messager messager = null;public NameCheckScanner(ProcessingEnvironment processingEnv) {this.messager = processingEnv.getMessager();}/** * 此方法用于检查Java类 */@Overridepublic Void visitType(TypeElement e, Void p) {scan(e.getTypeParameters(), p);checkCamelCase(e, true);super.visitType(e, p);return null;}/** * 检查传入的Element是否符合驼式命名法，如果不符合，则输出警告信息 *  * @param e * @param b */private void checkCamelCase(Element e, boolean initialCaps) {String name = e.getSimpleName().toString();boolean previousUpper = false;boolean conventional = true;int firstCodePoint = name.codePointAt(0);if (Character.isUpperCase(firstCodePoint)) {previousUpper = true;if (!initialCaps) {messager.printMessage(Kind.WARNING, "名称：" + name + " 应当已小写字符开头", e);return;}} else if (Character.isLowerCase(firstCodePoint)) {if (initialCaps) {messager.printMessage(Kind.WARNING, "名称:" + name + " 应当已大写字母开否", e);return;}} else {conventional = false;}if (conventional) {int cp = firstCodePoint;for (int i = Character.charCount(cp); i < name.length(); i += Character.charCount(cp)) {cp = name.codePointAt(i);if (Character.isUpperCase(cp)) {if (previousUpper) {conventional = false;break;}previousUpper = true;} else {previousUpper = false;}}}if (!conventional) {messager.printMessage(Kind.WARNING, "名称:" + name + "应当符合驼式命名法（Camel Case Names）", e);}}/** * 检查方法命名是否合法 */@Overridepublic Void visitExecutable(ExecutableElement e, Void p) {if (e.getKind() == ElementKind.METHOD) {Name name = e.getSimpleName();if (name.contentEquals(e.getEnclosingElement().getSimpleName())) {messager.printMessage(Kind.WARNING, "一个普通方法:" + name + " 不应当与类名重复，避免与构造函数产生混淆", e);checkCamelCase(e, false);}}super.visitExecutable(e, p);return null;}/** * 检查变量是否合法 */@Overridepublic Void visitVariable(VariableElement e, Void p) {/* 如果这个Variable是枚举或常量，则按大写命名检查，否则按照驼式命名法规则检查 */if (e.getKind() == ElementKind.ENUM_CONSTANT || e.getConstantValue() != null || heuristicallyConstant(e)) {checkAllCaps(e);} else {checkCamelCase(e, false);}super.visitVariable(e, p);return null;}/** * 大写命名检查，要求第一个字符必须是大写的英文字母，其余部分可以下划线或大写字母 *  * @param e */private void checkAllCaps(VariableElement e) {String name = e.getSimpleName().toString();boolean conventional = true;int firstCodePoint = name.codePointAt(0);if (!Character.isUpperCase(firstCodePoint)) {conventional = false;} else {boolean previousUnderscore = false;int cp = firstCodePoint;for (int i = Character.charCount(cp); i < name.length(); i += Character.charCount(cp)) {cp = name.codePointAt(i);if (cp == (int) '_') {if (previousUnderscore) {conventional = false;break;}previousUnderscore = true;} else {previousUnderscore = false;if (!Character.isUpperCase(cp) && !Character.isDigit(cp)) {conventional = false;break;}}}}if (!conventional) {messager.printMessage(Kind.WARNING, "常量:" + name + " 应该全部以大写字母" + "或下划线命名，并且以字符开否", e);}}/** * 判断一个变量是否是常量 *  * @param e * @return */private boolean heuristicallyConstant(VariableElement e) {if (e.getEnclosingElement().getKind() == ElementKind.INTERFACE) {return true;} else if (e.getKind() == ElementKind.FIELD && e.getModifiers().containsAll(EnumSet.of(javax.lang.model.element.Modifier.FINAL, javax.lang.model.element.Modifier.STATIC, javax.lang.model.element.Modifier.PUBLIC))) {return true;}return false;}}}}

在写一个测试类：

import java.util.ArrayList;import java.util.List;public class FT {public static class A_B_C {}public static String ab_sd="";public static int method(List<Integer> list) {System.out.println("method(List<Integer>list)");return 1;}public static void main(String[] args) {method(new ArrayList<Integer>());Long aLong = 2l;Integer aInteger = 1;Integer bInteger = 1;System.out.println(aLong.equals(aInteger + bInteger));System.out.println(aInteger.equals(1L));System.out.println("true");}}

接下来让我们进入到命令行试试

javac NameCheckProcessor.java 

javac -processor NameCheckProcessor FT.java

FT.java:4: 警告: 名称:FT应当符合驼式命名法（Camel Case Names）

public class FT {

       ^

1 个警告