Play源代码分析：Server启动过程

Play是个Rails风格的Java Web框架，需要了解背景请看：

1. Play Framework介绍1--主要概念
2. Play Framework介绍2—Helloworld

如何调试请看此处。以下进入正题^_^

Server启动过程主要涉及三个地方：

1. play.Play类：代表Play本身业务模型。
2. play.server.Server类：负责服务器启动。
3. play.classloading包：负责.java文件读取、编译和加载。

总体流程：

Server.main为入口方法：

public static void main(String[] args) throws Exception {
        …
        Play.init(root, System.getProperty("play.id", ""));
        if (System.getProperty("precompile") == null) {
            new Server();
        } else {
            Logger.info("Done.");
        }
    }

做两件事：

1. Play.init
2. 然后创建Server对象。

Play.init

public static void init(File root, String id) {

…

readConfiguration();

         Play.classes = new ApplicationClasses();

        …

        // Build basic java source path
        VirtualFile appRoot = VirtualFile.open(applicationPath);
        roots.add(appRoot);
        javaPath = new ArrayList<VirtualFile>(2);
        javaPath.add(appRoot.child("app"));
        javaPath.add(appRoot.child("conf"));

        // Build basic templates path
        templatesPath = new ArrayList<VirtualFile>(2);
        templatesPath.add(appRoot.child("app/views"));

        // Main route file
        routes = appRoot.child("conf/routes");

        …

        // Load modules
        loadModules();

        …

        // Enable a first classloader
        classloader = new ApplicationClassloader();

        // Plugins
        loadPlugins();

        // Done !
        if (mode == Mode.PROD ||preCompile() ) {
                start();
            }

        …
    }

主要做：

1. 加载配置
2. new ApplicationClasses();加载app、views和conf路径到VirtualFile中，VirtualFile是Play内部的统一文件访问接口，方便后续读取文件
3. 加载route
4. 加载Module，Play的应用扩展组件。
5. 加载Plugin，Play框架自身的扩展组件。
6. 工作在产品模式则启动Play.

关键步骤为new ApplicationClasses(),执行computeCodeHashe(),后者触发目录扫描，搜索.java文件。相关过程简化代码如下：

public ApplicationClassloader() {
        super(ApplicationClassloader.class.getClassLoader());
        // Clean the existing classes
        for (ApplicationClass applicationClass : Play.classes.all()) {
            applicationClass.uncompile();
        }
        pathHash = computePathHash();
       …
    }

int computePathHash() {
        StringBuffer buf = new StringBuffer();
        for (VirtualFile virtualFile : Play.javaPath) {
            scan(buf, virtualFile);
        }
        return buf.toString().hashCode();
    }

void scan(StringBuffer buf, VirtualFile current) {
        if (!current.isDirectory()) {
            if (current.getName().endsWith(".java")) {
                Matcher matcher = Pattern.compile("\\s+class\\s([a-zA-Z0-9_]+)\\s+").matcher(current.contentAsString());
                buf.append(current.getName());
                buf.append("(");
                while (matcher.find()) {
                    buf.append(matcher.group(1));
                    buf.append(",");
                }
                buf.append(")");
            }
        } else if (!current.getName().startsWith(".")) {
            for (VirtualFile virtualFile : current.list()) {
                scan(buf, virtualFile);
            }
        }
    }

简化代码如下：

public static synchronized void start() {
        try {
                        ...
            // Reload configuration
            readConfiguration();

                        ...

            // Try to load all classes
            Play.classloader.getAllClasses();

            // Routes
            Router.detectChanges(ctxPath);

            // Cache
            Cache.init();

            // Plugins
            for (PlayPlugin plugin : plugins) {
                try {
                    plugin.onApplicationStart();
                } catch(Exception e) {
                    if(Play.mode.isProd()) {
                        Logger.error(e, "Can't start in PROD mode with errors");
                    }
                    if(e instanceof RuntimeException) {
                        throw (RuntimeException)e;
                    }
                    throw new UnexpectedException(e);
                }
            }

            ...

            // Plugins
            for (PlayPlugin plugin : plugins) {
                plugin.afterApplicationStart();
            }

        } catch (PlayException e) {
            started = false;
            throw e;
        } catch (Exception e) {
            started = false;
            throw new UnexpectedException(e);
        }
    }

关键步骤为执行Play.classloader.getAllClasses()加载app目录中的类型。简化代码如下：

public List<Class> getAllClasses() {
        if (allClasses == null) {
            allClasses = new ArrayList<Class>();

            if (Play.usePrecompiled) {
                ...
            } else {
                List<ApplicationClass> all = new ArrayList<ApplicationClass>();

                // Let's plugins play
                for (PlayPlugin plugin : Play.plugins) {
                    plugin.compileAll(all);
                }

                for (VirtualFile virtualFile : Play.javaPath) {
                    all.addAll(getAllClasses(virtualFile));
                }
                List<String> classNames = new ArrayList<String>();
                for (int i = 0; i < all.size(); i++) {
                    if (all.get(i) != null && !all.get(i).compiled) {
                        classNames.add(all.get(i).name);
                    }
                }

                Play.classes.compiler.compile(classNames.toArray(new String[classNames.size()]));

                for (ApplicationClass applicationClass : Play.classes.all()) {
                    Class clazz = loadApplicationClass(applicationClass.name);
                    if (clazz != null) {
                        allClasses.add(clazz);
                    }
                }
                                ...
            }
        }
        return allClasses;
    }

主要步骤：

1. plugin.compileAll，给所有plugin一次机会进行自定义编译。
2. Play.classes.compiler.compile(classNames.toArray(new String[classNames.size()]));编译所有.java文件。编译后的.class存储在ApplicationClass中。内部使用了eclipse的JDT编译器。
3. loadApplicationClass，取出ApplicationClass中的.class加入List<Class>中返回。

到此完成.java的加载。相关对象关系如下图：

接着new Server()启动HTTP服务，监听请求

简化代码如下：

public Server() {
             ...
        if (httpPort == -1 && httpsPort == -1) {
            httpPort = 9000;
        }
        ...
        InetAddress address = null;
        try {
            if (p.getProperty("http.address") != null) {
                address = InetAddress.getByName(p.getProperty("http.address"));
            } else if (System.getProperties().containsKey("http.address")) {
                address = InetAddress.getByName(System.getProperty("http.address"));
            }

        } catch (Exception e) {
            Logger.error(e, "Could not understand http.address");
            System.exit(-1);
        }

        ServerBootstrap bootstrap = new ServerBootstrap(new NioServerSocketChannelFactory(
                Executors.newCachedThreadPool(), Executors.newCachedThreadPool())
        );
        try {
            if (httpPort != -1) {
                bootstrap.setPipelineFactory(new HttpServerPipelineFactory());
                bootstrap.bind(new InetSocketAddress(address, httpPort));
                bootstrap.setOption("child.tcpNoDelay", true);

                if (Play.mode == Mode.DEV) {
                    if (address == null) {
                        Logger.info("Listening for HTTP on port %s (Waiting a first request to start) ...", httpPort);
                    } else {
                        Logger.info("Listening for HTTP at %2$s:%1$s (Waiting a first request to start) ...", httpPort, address);
                    }
                } else {
                    if (address == null) {
                        Logger.info("Listening for HTTP on port %s ...", httpPort);
                    } else {
                        Logger.info("Listening for HTTP at %2$s:%1$s  ...", httpPort, address);
                    }
                }

            }

        } catch (ChannelException e) {
            Logger.error("Could not bind on port " + httpPort, e);
            System.exit(-1);
        }
        ...
    }

主要步骤：

1. 设置端口，地址
2. new ServerBootstrap，创建jboss netty服务器。Play1.1.1使用了netty作为底层通讯服务器。
3. new HttpServerPipelineFactory(),设置netty所需的请求处理管道工厂。它负责当请求到达时提供处理者。
4. bootstrap.bind(new InetSocketAddress(address, httpPort)，绑定地址，端口。

到此万事具备，只等东风了…