缘由

相信大家都用过 javadoc 命令或者 IDE 封装命令生成 java api doc 文档吧，但是你有没有反思过 javadoc 命令是怎么解析文件生成的呢？其实 javadoc 在 jdk 目录下只是一个可执行程序，但是这个可执行程序是基于 jdk 的 tools.jar 的一个封装，也就是说 javadoc 实现在 tools.jar 中。

很多时候我们可能会有一些奇葩的需求，譬如获取 java 文档注释搞事情，我们该怎样解析 java 文件去获取这些注释信息呢？你可能一开始想过使用正则匹配，但是这个方案其实是有兼容性问题的。或者说，你考虑过使用一些第三方库来解析 java 源码文件，但是这些库很多都是针对 java 源码的，而非源码中的注释。所以有一个超级棒的方案就是自定义 doclet，采用 javadoc 操作。

方案验证

既然说到这个方案依赖 javadoc 和 doclet，那就先去看看这方面的文档进行一下技术评估，具体参见 oracle 官方文档：

• javadoc doclet

• javadoc tools

javadoc 源码：

public final class javadoc extends ListResourceBundle {
    public javadoc() {
    }

    protected final Object[][] getContents() {
        return new Object[][]{{"javadoc.Body_missing_from_html_file", "Body tag missing from HTML file"}, {"javadoc.End_body_missing_from_html_file", "Close body tag missing from HTML file"}, {"javadoc.File_Read_Error", "Error while reading file {0}"}, {"javadoc.JavaScript_in_comment", "JavaScript found in documentation comment.\nUse --allow-script-in-comments to allow use of JavaScript."}, {"javadoc.Multiple_package_comments", "Multiple sources of package comments found for package \"{0}\""}, {"javadoc.class_not_found", "Class {0} not found."}, {"javadoc.error", "error"}, {"javadoc.error.msg", "{0}: error - {1}"}, {"javadoc.note.msg", "{1}"}, {"javadoc.note.pos.msg", "{0}: {1}"}, {"javadoc.warning", "warning"}, {"javadoc.warning.msg", "{0}: warning - {1}"}, {"main.Building_tree", "Constructing Javadoc information..."}, {"main.Loading_source_file", "Loading source file {0}..."}, {"main.Loading_source_files_for_package", "Loading source files for package {0}..."}, {"main.No_packages_or_classes_specified", "No packages or classes specified."}, {"main.Xusage", "  -Xmaxerrs <number>               Set the maximum number of errors to print\n  -Xmaxwarns <number>              Set the maximum number of warnings to print\n"}, {"main.Xusage.foot", "These options are non-standard and subject to change without notice."}, {"main.cant.read", "cannot read {0}"}, {"main.doclet_class_not_found", "Cannot find doclet class {0}"}, {"main.doclet_method_must_be_static", "In doclet class {0}, method {1} must be static."}, {"main.doclet_method_not_accessible", "In doclet class {0},  method {1} not accessible"}, {"main.doclet_method_not_found", "Doclet class {0} does not contain a {1} method"}, {"main.done_in", "[done in {0} ms]"}, {"main.error", "{0} error"}, {"main.errors", "{0} errors"}, {"main.exception_thrown", "In doclet class {0},  method {1} has thrown an exception {2}"}, {"main.fatal.error", "fatal error"}, {"main.fatal.exception", "fatal exception"}, {"main.file_not_found", "File not found: \"{0}\""}, {"main.illegal_locale_name", "Locale not available: {0}"}, {"main.illegal_package_name", "Illegal package name: \"{0}\""}, {"main.incompatible.access.flags", "More than one of -public, -private, -package, or -protected specified."}, {"main.internal_error_exception_thrown", "Internal error: In doclet class {0},  method {1} has thrown an exception {2}"}, {"main.invalid_flag", "invalid flag: {0}"}, {"main.locale_first", "option -locale must be first on the command line."}, {"main.malformed_locale_name", "Malformed locale name: {0}"}, {"main.more_than_one_doclet_specified_0_and_1", "More than one doclet specified ({0} and {1})."}, {"main.must_return_boolean", "In doclet class {0}, method {1} must return boolean."}, {"main.must_return_int", "In doclet class {0}, method {1} must return int."}, {"main.must_return_languageversion", "In doclet class {0}, method {1} must return LanguageVersion."}, {"main.no_source_files_for_package", "No source files for package {0}"}, {"main.option.already.seen", "The {0} option may be specified no more than once."}, {"main.out.of.memory", "java.lang.OutOfMemoryError: Please increase memory.\nFor example, on the JDK Classic or HotSpot VMs, add the option -J-Xmx\nsuch as -J-Xmx32m."}, {"main.requires_argument", "option {0} requires an argument."}, {"main.usage", "Usage: javadoc [options] [packagenames] [sourcefiles] [@files]\n  -overview <file>                 Read overview documentation from HTML file\n  -public                          Show only public classes and members\n  -protected                       Show protected/public classes and members (default)\n  -package                         Show package/protected/public classes and members\n  -private                         Show all classes and members\n  -help                            Display command line options and exit\n  -doclet <class>                  Generate output via alternate doclet\n  -docletpath <path>               Specify where to find doclet class files\n  -sourcepath <pathlist>           Specify where to find source files\n  -classpath <pathlist>            Specify where to find user class files\n  -cp <pathlist>                   Specify where to find user class files\n  -exclude <pkglist>               Specify a list of packages to exclude\n  -subpackages <subpkglist>        Specify subpackages to recursively load\n  -breakiterator                   Compute first sentence with BreakIterator\n  -bootclasspath <pathlist>        Override location of class files loaded\n                                   by the bootstrap class loader\n  -source <release>                Provide source compatibility with specified release\n  -extdirs <dirlist>               Override location of installed extensions\n  -verbose                         Output messages about what Javadoc is doing\n  -locale <name>                   Locale to be used, e.g. en_US or en_US_WIN\n  -encoding <name>                 Source file encoding name\n  -quiet                           Do not display status messages\n  -J<flag>                         Pass <flag> directly to the runtime system\n  -X                               Print a synopsis of nonstandard options and exit\n"}, {"main.warning", "{0} warning"}, {"main.warnings", "{0} warnings"}, {"tag.End_delimiter_missing_for_possible_SeeTag", "End Delimiter } missing for possible See Tag in comment string: \"{0}\""}, {"tag.Improper_Use_Of_Link_Tag", "Missing closing ''}'' character for inline tag: \"{0}\""}, {"tag.illegal_char_in_arr_dim", "Tag {0}: Syntax Error in array dimension, method parameters: {1}"}, {"tag.illegal_see_tag", "Tag {0}: Syntax Error in method parameters: {1}"}, {"tag.missing_comma_space", "Tag {0}: Missing comma or space in method parameters: {1}"}, {"tag.see.can_not_find_member", "Tag {0}: can''t find {1} in {2}"}, {"tag.see.class_not_specified", "Tag {0}: class not specified: \"{1}\""}, {"tag.see.illegal_character", "Tag {0}:illegal character: \"{1}\" in \"{2}\""}, {"tag.see.malformed_see_tag", "Tag {0}: malformed: \"{1}\""}, {"tag.see.missing_sharp", "Tag {0}: missing ''#'': \"{1}\""}, {"tag.see.no_close_bracket_on_url", "Tag {0}: missing final ''>'': \"{1}\""}, {"tag.see.no_close_quote", "Tag {0}: no final close quote: \"{1}\""}, {"tag.serialField.illegal_character", "illegal character {0} in @serialField tag: {1}."}, {"tag.tag_has_no_arguments", "{0} tag has no arguments."}};
    }
}

Doclet 源码：

public abstract class Doclet {
    public Doclet() {
    }

    public static boolean start(RootDoc var0) {
        return true;
    }

    public static int optionLength(String var0) {
        return 0;
    }

    public static boolean validOptions(String[][] var0, DocErrorReporter var1) {
        return true;
    }

    public static LanguageVersion languageVersion() {
        return LanguageVersion.JAVA_1_1;
    }
}

通过文档我们可以发现，其实我们只用自定义一个 Doclet 类就行了，至于怎么定义其实文档中已经写的很详细了，还给出了具体代码片段，我们可以直接搬过来进行验证即可，代码如下：

public class CustomerDoclet extends Doclet {
  public static boolean start(RootDoc root) {
    ClassDoc[] classes = root.classes();
    //注释文档信息，自己爱怎么解析组织就怎么解析了，看自己需求 
    return true;
  }
｝

public static void main(String[] args) {
     String[] docArgs =
         new String[] {
           "-doclet", CustomerDoclet.class.getName(), "/home/yan/test/cn/test/JavaSource.java"
         };
     com.sun.tools.javadoc.Main.execute(docArgs);
}

简单吧，运行上面代码段就能自定义 javadoc 输出解析了。跑了下发现没问题，那就开始搞事情吧。

实现一个 gradle 插件进行 javadoc 自定义操作

这里我们为了简单和直接说明核心，所以打算实现一个检查 android、androidLibrary、java、javaLibrary 代码源文件中是否包含 javadoc @author 的插件，插件名称 gradle-javadoc-checker，具体完整插件源码可以访问 https://github.com/yanbober/gradle-javadoc-checker 获取。

注意：这部分内容需要你先对 gradle 插件开发比较熟悉才能看懂，所以建议先掌握所说的知识后进行研读。

添加依赖

dependencies {
    compile gradleApi()
    compile 'com.android.tools.build:gradle:3.1.0'
    //tools.jar 的依赖
    compile files(org.gradle.internal.jvm.Jvm.current().toolsJar)
}

编写自定义 javadoc 判断 @author 工具

public class JavaDocReader {
    private static RootDoc root;
    //自定义 doclet
    public static class CustomerDoclet {
        public static boolean start(RootDoc root) {
            JavaDocReader.root = root;
            return true;
        }
    }
    
    //tools.jar 中 javadoc 的封装
    public static RootDoc process(String[] extraArges) {
        List<String> argsOrderList = new ArrayList<>();
        argsOrderList.add("-doclet");
        argsOrderList.add(CustomerDoclet.class.getName());
        argsOrderList.addAll(Arrays.asList(extraArges));
        String[] args = argsOrderList.toArray(new String[argsOrderList.size()]);
        System.out.println(args);
        Main.execute(args);
        return root;
    }

    //tools.jar 中 javadoc 的封装
    public static void process(List<String> sourcePaths, List<String> javapackages,
                               List<String> excludePackages, String outputDir) throws Exception {
        String paths = list2formatString(sourcePaths, ";");
        String includes = list2formatString(javapackages, ":");
        String excludes = list2formatString(excludePackages, ":");

        List<String> argsOrderList = new ArrayList<>();
        argsOrderList.add("-doclet");
        argsOrderList.add(CustomerDoclet.class.getName());

        if (paths != null && paths.length() > 0) {
            argsOrderList.add("-sourcepath");
            argsOrderList.add(paths);
        }

        argsOrderList.add("-encoding");
        argsOrderList.add("utf-8");
        argsOrderList.add("-verbose");

        if (includes != null && includes.length() > 0) {
            argsOrderList.add("-subpackages");
            argsOrderList.add(includes);
        }

        if (excludes != null && excludes.length() > 0) {
            argsOrderList.add("-exclude");
            argsOrderList.add(excludes);
        }

        String[] args = argsOrderList.toArray(new String[argsOrderList.size()]);
        System.out.println(Arrays.toString(args));
        //执行 tools.jar 中的 javadoc 命令
        Main.execute(args);

        File file = new File(outputDir);
        if (!file.exists()) {
            file.mkdirs();
        }
        file = new File(file, new Date().toString() + ".txt");
        FileOutputStream outputStream = new FileOutputStream(file);
        //判断每个顶级 java class 是否有编写 @author 人，没有就筛出来写入一个文件记录
        ClassDoc[] classes = root.classes();
        if (classes != null) {
            for (int i = 0; i < classes.length; ++i) {
                if (classes[i].containingClass() == null && classes[i].isPublic()) {
                    Tag[] authorTags = classes[i].tags("author");
                    if (authorTags == null || authorTags.length == 0) {
                        String filename = classes[i].position().file().getAbsolutePath();
                        outputStream.write((filename+"\r\n").getBytes());
                    }
                }
            }
        }
        root = null;
        outputStream.flush();
        outputStream.close();
    }

    private static String list2formatString(List<String> srcs, String div) {
        StringBuilder stringBuilder = new StringBuilder();
        for (int index=0; index<srcs.size(); index++) {
            if (index > 0) {
                stringBuilder.append(div);
            }
            stringBuilder.append(srcs.get(index));
        }
        return stringBuilder.toString();
    }
}

有了 javadoc 自定义工具类，接下来编写 gradle 自定义 task 即可。

编写自定义 gradle task 进行检查

//groovy 编写
class JavaDocCheckerTask extends DefaultTask {
    //自定义 task 的输入
    @Input
    List<String> includePackages

    @Input
    List<String> excludePackages

    @Input
    List<String> sourcePaths

    //自定义 task 的输出
    @OutputDirectory
    String outputDir

    //自定义 task 的执行逻辑
    @TaskAction
    void checker() {
        if (sourcePaths == null || sourcePaths.size() == 0) {
            throw new GradleScriptException("JavaDocCheckerTask sourcePaths params can't be null or empty!")
        }

        if (outputDir == null || outputDir.length() == 0) {
            throw new GradleScriptException("JavaDocCheckerTask outputDir params can't be null or empty!")
        }
        //task 依据输出输出参数进行 javadoc 命令操作
        JavaDocReader.process(sourcePaths, includePackages, excludePackages, outputDir)
    }
}

有了自定义 gradle task 进行 javadoc 操作，接下来就该接入插件了。

将自定义 task 加入构建 project

先定义插件的 extension 拓展参数：

class CheckerExtension {
    public static final String NAME = "javadocChecker"

    List<String> includePackages

    List<String> excludePackages

    List<String> sourcePaths

    String outputDirectory
}

将拓展参数与 task 结合：

class JavaDocCheckerPlugin implements Plugin<Project> {
    @Override
    void apply(Project project) {
        //插件添加自定义 extension
        project.extensions.create(CheckerExtension.NAME, CheckerExtension)
        //将自定义任务加入 project
        project.tasks.create("javaDocChecker", JavaDocCheckerTask)

        //依据 apply 的是 java、androidlibrary、androidapplication 分别获取对应的拓展参数
        JavaPluginConvention java = null
        BaseExtension android = null
        if (project.plugins.hasPlugin(AppPlugin)) {
            android = project.extensions.getByType(AppExtension)
        } else if(project.plugins.hasPlugin(LibraryPlugin)) {
            android = project.extensions.getByType(LibraryExtension)
        } else if (project.plugins.hasPlugin(JavaPlugin)) {
            java = project.convention.getPlugin(JavaPluginConvention)
        }

        if (java == null && android == null) {
            throw new GradleException("it's a not support plugin type!")
        }

        project.afterEvaluate {
            afterEvaluateInner(project, java, android)
        }
    }

    private void afterEvaluateInner(Project project, JavaPluginConvention java, BaseExtension android) {
        if (java != null) {
            //java 插件就进行 java 的 sourceSets 处理
            processJava(project, java)
        } else if (android != null) {
            //Android 插件就进行 android 的 sourceSets 处理
            processAndroid(project, android)
        }
    }

    private void processJava(Project project, JavaPluginConvention java) {
        List<String> sources = new ArrayList<>()
        //拿到 java sourceSets main 的 src 进行检查处理
        SourceSet mainSourceSet = java.sourceSets.getByName(SourceSet.MAIN_SOURCE_SET_NAME)
        mainSourceSet.allJava.srcDirs.each {
            sources.add(it.absolutePath)
        }

        assignedTask(project, sources)
    }

    private void processAndroid(Project project, BaseExtension android) {
        List<String> sources = new ArrayList<>()
        //拿到 android sourceSets main 的 src 进行检查处理
        AndroidSourceSet mainSourceSet = android.sourceSets.getByName(SourceSet.MAIN_SOURCE_SET_NAME)
        mainSourceSet.java.srcDirs.each {
            sources.add(it.absolutePath)
        }

        assignedTask(project, sources)
    }

    //把插件 extension 的自定义属性赋值给自定义 task 的 input 和 output
    private void assignedTask(Project project, List<String> sources) {
        def checker = project[CheckerExtension.NAME]
        if (checker == null) {
            return
        }

        project.getTasksByName("javaDocChecker", false).each {
            it.configure {
                includePackages = checker.includePackages == null ? [] : checker.includePackages
                excludePackages = checker.excludePackages == null ? [] : checker.excludePackages
                sourcePaths = sources
                outputDir = checker.outputDirectory
            }
        }
    }
}

到此插件核心主体就开发完了，然后就可以使用了，这就是一个完整的通过自定义 javadoc 输出来解决实际问题的小项目，感兴趣可以访问项目源码进行研究，也可以自定义自己的操作。具体完整插件源码可以访问 https://github.com/yanbober/gradle-javadoc-checker 获取。

总结

本文给出了一个实现思路，你可以发现，doclet 简直就是一个巨无霸，对于 java doc 文档操作只有你想不到的，没有他做不到的。希望对你有所启发。

本文引用自 JDK tools.jar 中 javadoc 自定义 doclet 的妙用