一、Gradle Transform到底是什么

Gradle Transform是Android官方提供給開發者在項目構建階段（.class -> .dex轉換期間）用來修改.class文件的一套標準API，即把輸入的.class文件轉變成目標字節碼文件，目前比較經典的應用是字節碼插樁、代碼注入等。

二、Gradle Transform怎么用

1、在build.gradle文件中添加Gradle插件依賴

buildscript {    dependencies {        classpath 'com.android.tools.build:gradle:x.x.x'        // 其他插件依賴    }}apply plugin: 'com.android.application' // 或其他所需插件

2、編寫Transform類

編寫Transform類，在其中實現對Java字節碼進行的修改。Transform類需要繼承自Transform接口并實現其兩個方法：

public class MyTransform extends Transform {   @Override   public String getName() {       return "myTransform";   }   @Override   public Set getInputTypes() {       return TransformManager.CONTENT_CLASS;   }   @Override   public Set getScopes() {       return TransformManager.SCOPE_FULL_PROJECT;   }   @Override   public boolean isIncremental() {       return false;   }   @Override   public void transform(TransformInvocation transformInvocation) throws TransformException, InterruptedException, IOException {       // 實現Transform邏輯   }}

3、配置Transform

在build.gradle文件中配置Transform，將其作為編譯期間的一個任務執行：

android {    ...    // 配置Transform    transformClassesWithMyTransformForDebug {        // 可選配置項，如下所示        // enable false        // ignoreWarnings true        // enableTransformForJar false    }}dependencies {    ...}

完成以上步驟后，Gradle會在編譯期間執行Transform對Java字節碼進行修改，從而實現各種自動生成代碼、字節碼增強等功能。

三、Transform編寫模板

1、無增量編譯

AspectJTransform.groovy代碼如下：

class AspectJTransform extends Transform {    final String NAME =  "JokerwanTransform"    @Override    String getName() {        return NAME    }    @Override    Set getInputTypes() {        return TransformManager.CONTENT_CLASS    }    @Override    Set getScopes() {        return TransformManager.SCOPE_FULL_PROJECT    }    @Override    boolean isIncremental() {        return false    }      @Override    void transform(TransformInvocation transformInvocation) throws TransformException, InterruptedException, IOException {        super.transform(transformInvocation)        // OutputProvider管理輸出路徑，如果消費型輸入為空，你會發現OutputProvider == null        TransformOutputProvider outputProvider = transformInvocation.getOutputProvider();        transformInvocation.inputs.each { TransformInput input ->            input.jarInputs.each { JarInput jarInput ->                // 處理Jar                processJarInput(jarInput, outputProvider)            }            input.directoryInputs.each { DirectoryInput directoryInput ->                // 處理源碼文件                processDirectoryInputs(directoryInput, outputProvider)            }        }    }    void processJarInput(JarInput jarInput, TransformOutputProvider outputProvider) {        File dest = outputProvider.getContentLocation(                jarInput.getFile().getAbsolutePath(),                jarInput.getContentTypes(),                jarInput.getScopes(),                Format.JAR)                        // to do some transform                // 將修改過的字節碼copy到dest，就可以實現編譯期間干預字節碼的目的了                FileUtils.copyFiley(jarInput.getFile(), dest)    }    void processDirectoryInputs(DirectoryInput directoryInput, TransformOutputProvider outputProvider) {        File dest = outputProvider.getContentLocation(directoryInput.getName(),                directoryInput.getContentTypes(), directoryInput.getScopes(),                Format.DIRECTORY)        // 建立文件夾                FileUtils.forceMkdir(dest)                // to do some transform                // 將修改過的字節碼copy到dest，就可以實現編譯期間干預字節碼的目的了                FileUtils.copyDirectory(directoryInput.getFile(), dest)    }}

2、有增量編譯

AspectJTransform.groovy代碼如下：

class AspectJTransform extends Transform {    final String NAME = "JokerWanTransform"    @Override    String getName() {        return NAME    }    @Override    Set getInputTypes() {        return TransformManager.CONTENT_CLASS    }    @Override    Set getScopes() {        return TransformManager.SCOPE_FULL_PROJECT    }    @Override    boolean isIncremental() {        return true    }    @Override    void transform(TransformInvocation transformInvocation) throws TransformException, InterruptedException, IOException {        super.transform(transformInvocation)        boolean isIncremental = transformInvocation.isIncremental()        // OutputProvider管理輸出路徑，如果消費型輸入為空，你會發現OutputProvider == null        TransformOutputProvider outputProvider = transformInvocation.getOutputProvider()        if (!isIncremental) {            // 不需要增量編譯，先清除全部            outputProvider.deleteAll()        }        transformInvocation.getInputs().each { TransformInput input ->            input.jarInputs.each { JarInput jarInput ->                // 處理Jar                processJarInputWithIncremental(jarInput, outputProvider, isIncremental)            }            input.directoryInputs.each { DirectoryInput directoryInput ->                // 處理文件                processDirectoryInputWithIncremental(directoryInput, outputProvider, isIncremental)            }        }    }    void processJarInputWithIncremental(JarInput jarInput, TransformOutputProvider outputProvider, boolean isIncremental) {        File dest = outputProvider.getContentLocation(                jarInput.getFile().getAbsolutePath(),                jarInput.getContentTypes(),                jarInput.getScopes(),                Format.JAR)        if (isIncremental) {            // 處理增量編譯            processJarInputWhenIncremental(jarInput, dest)        } else {            // 不處理增量編譯            processJarInput(jarInput, dest)        }    }    void processJarInput(JarInput jarInput, File dest) {        transformJarInput(jarInput, dest)    }    void processJarInputWhenIncremental(JarInput jarInput, File dest) {        switch (jarInput.status) {            case Status.NOTCHANGED:                break            case Status.ADDED:            case Status.CHANGED:                // 處理有變化的                transformJarInputWhenIncremental(jarInput.getFile(), dest, jarInput.status)                break            case Status.REMOVED:                // 移除Removed                if (dest.exists()) {                    FileUtils.forceDelete(dest)                }                break        }    }    void transformJarInputWhenIncremental(JarInput jarInput, File dest, Status status) {        if (status == Status.CHANGED) {            // Changed的狀態需要先刪除之前的            if (dest.exists()) {                FileUtils.forceDelete(dest)            }        }        // 真正transform的地方        transformJarInput(jarInput, dest)    }    void transformJarInput(JarInput jarInput, File dest) {            // to do some transform                // 將修改過的字節碼copy到dest，就可以實現編譯期間干預字節碼的目的了        FileUtils.copyFile(jarInput.getFile(), dest)    }    void processDirectoryInputWithIncremental(DirectoryInput directoryInput, TransformOutputProvider outputProvider, boolean isIncremental) {        File dest = outputProvider.getContentLocation(                directoryInput.getFile().getAbsolutePath(),                directoryInput.getContentTypes(),                directoryInput.getScopes(),                Format.DIRECTORY)        if (isIncremental) {            // 處理增量編譯            processDirectoryInputWhenIncremental(directoryInput, dest)        } else {            processDirectoryInput(directoryInput, dest)        }    }    void processDirectoryInputWhenIncremental(DirectoryInput directoryInput, File dest) {        FileUtils.forceMkdir(dest)        String srcDirPath = directoryInput.getFile().getAbsolutePath()        String destDirPath = dest.getAbsolutePath()        Map fileStatusMap = directoryInput.getChangedFiles()        fileStatusMap.each { Map.Entry entry ->            File inputFile = entry.getKey()            Status status = entry.getValue()            String destFilePath = inputFile.getAbsolutePath().replace(srcDirPath, destDirPath)            File destFile = new File(destFilePath)            switch (status) {                case Status.NOTCHANGED:                    break                case Status.REMOVED:                    if (destFile.exists()) {                        FileUtils.forceDelete(destFile)                    }                    break                case Status.ADDED:                case Status.CHANGED:                    FileUtils.touch(destFile)                    transformSingleFile(inputFile, destFile, srcDirPath)                    break            }        }    }    void processDirectoryInput(DirectoryInput directoryInput, File dest) {        transformDirectoryInput(directoryInput, dest)    }    void transformDirectoryInput(DirectoryInput directoryInput, File dest) {            // to do some transform                // 將修改過的字節碼copy到dest，就可以實現編譯期間干預字節碼的目的了        FileUtils.copyDirectory(directoryInput.getFile(), dest)    }    void transformSingleFile(File inputFile, File destFile, String srcDirPath) {        FileUtils.copyFile(inputFile, destFile)    }}

延伸閱讀1：TransformInput

TransformInput是指輸入文件的一個抽象，包括：