如果你也有一个老旧的Java Web应用，因为各种原因，代码库中的代码是不完整的，所以每次上线只能增量部署，或者研发规范里就要求增量部署，在这种情况下如何实现自动化的编译和部署呢？下面给出一个可行的方案：

    1、部署前，将需要部署的代码合并到deliver分支

    2、比较deliver分支和master分支的差异，得到差异列表之后，用于后续的编译

    3、编译差异文件时，需要将应用所依赖的jar，已经部署的class文件等加入到CLASSPATH

    4、如果各测试环境也使用这一套自动部署的方案，可能还需要考虑剥离环境相关的配置到配置文件中，并根据环境分目录存放，具体可以参考maven的profile机制

    核心代码（代码结构请自行优化 :D）：

    1、比较两个分支的差异（忽略whitespace带来的差异）：

        try (Git git = Git.open(gitRepoFile);                 ByteArrayOutputStream out = new ByteArrayOutputStream();                 DiffFormatter df = new DiffFormatter(out);) {              Repository repository = git.getRepository();             ObjectReader reader = repository.newObjectReader();              String branchName = repository.getBranch();              ObjectId masterId = repository.resolve("remotes/origin/master^{tree}");             ObjectId branchId = repository.resolve(branchName + "^{tree}");              CanonicalTreeParser masterTreeParser = new CanonicalTreeParser();             masterTreeParser.reset(reader, masterId);              CanonicalTreeParser branchTreeParser = new CanonicalTreeParser();             branchTreeParser.reset(reader, branchId);              List<DiffEntry> diffs = git.diff()                     .setNewTree(branchTreeParser)                     .setOldTree(masterTreeParser)                     .call();              Map<String, List<String>> diffFileMap = new HashMap<>();             List<String> changeFileList = new ArrayList<>();             List<String> deleteFileList = new ArrayList<>();              df.setDiffComparator(RawTextComparator.WS_IGNORE_ALL);             df.setRepository(git.getRepository());              for (DiffEntry diffEntry : diffs) {                 df.format(diffEntry);                 FileHeader fileHeader = df.toFileHeader(diffEntry);                  @SuppressWarnings("unchecked")                 List<HunkHeader> hunks = (List<HunkHeader>) fileHeader.getHunks();                 int changedSize = 0;                 for (HunkHeader hunkHeader : hunks) {                     EditList editList = hunkHeader.toEditList();                     for (Edit edit : editList) {                         changedSize += edit.getEndA() - edit.getBeginA();                         changedSize += edit.getEndB() - edit.getBeginB();                     }                 }                  if (changedSize > 0) {                     ChangeType changeType = diffEntry.getChangeType();                     if (ChangeType.DELETE.equals(changeType)) {                         String oldFilePath = diffEntry.getOldPath();                         log.info("{}|{}", changeType.name(), oldFilePath);                         deleteFileList.add(oldFilePath);                     } else {                         String newFilePath = diffEntry.getNewPath();                         log.info("{}|{}", changeType.name(), newFilePath);                         changeFileList.add(newFilePath);                     }                 }             }             diffFileMap.put("change", changeFileList);             diffFileMap.put("delete", deleteFileList);              return diffFileMap;         }

    2、编译：

        Iterable<String> options = Arrays.asList(                 "-classpath", classpath,                 "-encoding", encoding,                 "-source", jdkVersion,                 "-target", jdkVersion,                 "-d", targetPath);          JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();         log.info("classpath:{}", classpath);         log.info("targetPath:{}", targetPath);          try (StandardJavaFileManager fileManager = compiler.getStandardFileManager(null, null, null);) {              Iterable<? extends JavaFileObject> compilationUnits = fileManager.getJavaFileObjectsFromFiles(fileList);              DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<>();              CompilationTask compilationTask = compiler                     .getTask(null, fileManager, diagnostics, options, null, compilationUnits);              if (!compilationTask.call()) {                 log.error("JavaCompiler Build failed：");                  for (Diagnostic<?> diagnostic : diagnostics.getDiagnostics()) {                     long line = diagnostic.getLineNumber();                     String source = diagnostic.getSource() != null ? diagnostic.getSource().toString() : "";                     String kind = diagnostic.getKind().name();                     String message = diagnostic.getMessage(null);                     log.info("{} on line:{} in {}.", kind, line, source);                     log.info("message:{}", message);                 }                 return false;             }         }

    要实现完整的功能，还需要根据应用的具体情况完善，比如：从运行环境同步删除代码库中删除的文件；从代码库拉取文件时，用fetch，reset的方式；还可以借助Marathon、Mesos、Docker运行应用等。