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Tomcat探秘(4):tomcat启动过程详述

时间:2016-06-12 01:53:55      阅读:441      评论:0      收藏:0      [点我收藏+]

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熟悉Tomcat的工程师们,或者从事Java开发的,肯定都知道Tomcat是如何启动和停止的。在Tomcat源码包里面有个bin目录,该目录下放置了一些很重要的脚本,Tomcat启动和停止的脚本程序就放在这里,分别是startup.bat、shutdown.bat(Windows环境)和start.sh、shutdown.sh(Linux、Unix环境)。大家一定都知道如何使用它们,接下来就是研究一下它们是如何实现启动和停止服务的。

在实际的生产环境下,绝大多数的Tomcat都是部署在Linux环境下的,在这片文章中,我们以startup.sh和shutdown.sh为例简单说说启动和停止过程。(Tomcat版本7.0.69)

启动过程分析:

进入到Tomcat的bin目录,启动startup.sh的命令如下:

./startup.sh
该脚本里面都做了什么呢?这里贴出启动脚本:
#!/bin/sh

# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# -----------------------------------------------------------------------------
# Start Script for the CATALINA Server
# -----------------------------------------------------------------------------

# Better OS/400 detection: see Bugzilla 31132
os400=false
case "`uname`" in
OS400*) os400=true;;
esac

# resolve links - $0 may be a softlink
PRG="$0"

while [ -h "$PRG" ] ; do
  ls=`ls -ld "$PRG"`
  link=`expr "$ls" : '.*-> \(.*\)$'`
  if expr "$link" : '/.*' > /dev/null; then
    PRG="$link"
  else
    PRG=`dirname "$PRG"`/"$link"
  fi
done

PRGDIR=`dirname "$PRG"`
EXECUTABLE=catalina.sh

# Check that target executable exists
if $os400; then
  # -x will Only work on the os400 if the files are:
  # 1. owned by the user
  # 2. owned by the PRIMARY group of the user
  # this will not work if the user belongs in secondary groups
  eval
else
  if [ ! -x "$PRGDIR"/"$EXECUTABLE" ]; then
    echo "Cannot find $PRGDIR/$EXECUTABLE"
    echo "The file is absent or does not have execute permission"
    echo "This file is needed to run this program"
    exit 1
  fi
fi

exec "$PRGDIR"/"$EXECUTABLE" start "$@"

下面简单看看这个脚本,前面几行:
os400=false
case "`uname`" in
OS400*) os400=true;;
esac

使用uname查看当前操作系统的名称,然后判断是否符合模式OS400*,如果是则进行标记,设置os400=true,用于控制后面的逻辑。

在后面的脚本命令中,涉及到的两个比较重要的变量就是PRGDIR(当前startup.sh脚本的上一级目录,即bin目录)和EXECUTABLE(设置了脚本名称catalina.sh),然后最后通过执行

exec "$PRGDIR"/"$EXECUTABLE" start "$@"

来启动执行catalina.sh脚本并将start参数传递给脚本用于控制是进行启动操作的。因为catelina.sh脚本的代码较长,这里只贴出跟启动相关的部分指令:
...........
elif [<span style="color:#FF0000;"> "$1" = "start"</span> ] ; then

  <span style="color:#3366FF;">if [ ! -z "$CATALINA_PID" ]; then
    if [ -f "$CATALINA_PID" ]; then
      if [ -s "$CATALINA_PID" ]; then
        echo "Existing PID file found during start."
        if [ -r "$CATALINA_PID" ]; then
          PID=`cat "$CATALINA_PID"`
          ps -p $PID >/dev/null 2>&1
          if [ $? -eq 0 ] ; then
            echo "Tomcat appears to still be running with PID $PID. Start aborted."
            echo "If the following process is not a Tomcat process, remove the PID file and try again:"
            ps -f -p $PID
            exit 1
          else
            echo "Removing/clearing stale PID file."
            rm -f "$CATALINA_PID" >/dev/null 2>&1
            if [ $? != 0 ]; then
              if [ -w "$CATALINA_PID" ]; then
                cat /dev/null > "$CATALINA_PID"
              else
                echo "Unable to remove or clear stale PID file. Start aborted."
                exit 1
              fi
            fi
          fi
        else
          echo "Unable to read PID file. Start aborted."
          exit 1
        fi
      else
        rm -f "$CATALINA_PID" >/dev/null 2>&1
        if [ $? != 0 ]; then
          if [ ! -w "$CATALINA_PID" ]; then
            echo "Unable to remove or write to empty PID file. Start aborted."
            exit 1
          fi
        fi
      fi
    fi
  fi</span>

  shift
  touch "$CATALINA_OUT"
  if [ "$1" = "-security" ] ; then
    if [ $have_tty -eq 1 ]; then
      echo "Using Security Manager"
    fi
    shift
    eval "\"$_RUNJAVA\"" "\"$LOGGING_CONFIG\"" $LOGGING_MANAGER $JAVA_OPTS $CATALINA_OPTS       -Djava.endorsed.dirs="\"$JAVA_ENDORSED_DIRS\"" -classpath "\"$CLASSPATH\""       -Djava.security.manager       -Djava.security.policy=="\"$CATALINA_BASE/conf/catalina.policy\""       -Dcatalina.base="\"$CATALINA_BASE\""       -Dcatalina.home="\"$CATALINA_HOME\""       -Djava.io.tmpdir="\"$CATALINA_TMPDIR\""      <span style="color:#CC33CC;"> org.apache.catalina.startup.Bootstrap "$@" start       >> "$CATALINA_OUT" 2>&1 "&"</span>

  else
    eval "\"$_RUNJAVA\"" "\"$LOGGING_CONFIG\"" $LOGGING_MANAGER $JAVA_OPTS $CATALINA_OPTS       -Djava.endorsed.dirs="\"$JAVA_ENDORSED_DIRS\"" -classpath "\"$CLASSPATH\""       -Dcatalina.base="\"$CATALINA_BASE\""       -Dcatalina.home="\"$CATALINA_HOME\""       -Djava.io.tmpdir="\"$CATALINA_TMPDIR\""       <span style="color:#CC33CC;">org.apache.catalina.startup.Bootstrap "$@" start       >> "$CATALINA_OUT" 2>&1 "&"</span>

  fi

  if [ ! -z "$CATALINA_PID" ]; then
    echo $! > "$CATALINA_PID"
  fi

  echo "Tomcat started."

elif [ <span style="color:#FF0000;">"$1" = "stop"</span> ] ; then
.................

catalina.sh脚本是所有其他脚本最终实际执行操作的脚本,不管是启动还是停止脚本,执行startup.sh和shutdown.sh最终都会转换为执行catalina.sh,只是在执行catalina.sh时传递的参数不一样。

上面的红色部分就是判断是启动还是停止服务,而蓝色部分是对一些参数的校验工作,而从紫色部分可以看出,最终启动的时候是执行了org.apache.catalina.startup.Bootstrap这个类,同时传递了参数"start"。在之前的文章<Tomcat探秘(2):如何在Eclipse中导入和运行tomcat源代码?>中我们已经把Tomcat源码导入到了Eclipse中,这时候我们可以根据类包名路径找到相应的类Bootstrap,并且找到其main(),这里贴出main方法实现,如下所示:

/**
     * Main method and entry point when starting Tomcat via the provided
     * scripts.
     *
     * @param args Command line arguments to be processed
     */
    public static void main(String args[]) {

        if (daemon == null) {
            // Don't set daemon until init() has completed
            Bootstrap bootstrap = new Bootstrap();
            try {
                bootstrap.init();
            } catch (Throwable t) {
                handleThrowable(t);
                t.printStackTrace();
                return;
            }
            daemon = bootstrap;
        } else {
            // When running as a service the call to stop will be on a new
            // thread so make sure the correct class loader is used to prevent
            // a range of class not found exceptions.
            Thread.currentThread().setContextClassLoader(daemon.catalinaLoader);
        }

        try {
            String command = "start";
            if (args.length > 0) {
                command = args[args.length - 1];
            }

            if (command.equals("startd")) {
                args[args.length - 1] = "start";
                daemon.load(args);
                daemon.start();
            } else if (command.equals("stopd")) {
                args[args.length - 1] = "stop";
                daemon.stop();
            } <span style="color:#FF0000;">else if (command.equals("start")</span>) {
                daemon.setAwait(true);
                daemon.load(args);
                daemon.start();
            } else if (command.equals("stop")) {
                daemon.stopServer(args);
            } else if (command.equals("configtest")) {
                daemon.load(args);
                if (null==daemon.getServer()) {
                    System.exit(1);
                }
                System.exit(0);
            } else {
                log.warn("Bootstrap: command \"" + command + "\" does not exist.");
            }
        } catch (Throwable t) {
            // Unwrap the Exception for clearer error reporting
            if (t instanceof InvocationTargetException &&
                    t.getCause() != null) {
                t = t.getCause();
            }
            handleThrowable(t);
            t.printStackTrace();
            System.exit(1);
        }

    }

上面的标红部分就是根据传递进来的“start”参数来确定的分支逻辑。

从上面的main方法可以看出,整个启动过程大概分为三个步骤,如上面蓝色标记的部分:

(1)判断bootstrap是否已经初始化了?如果没有则进行初始化;

(2)调用Bootstrap类的load()来加载server.xml配置文件(这是一个很重要的配置文件);

(3)调用Bootstrap类的start()方法启动Tomcat;

下面对这三个步骤进行简单的描述。

第一步:判断bootstrap是否已经初始化了?如果没有则进行初始化;

通过上面的代码可以知道实际是通过调用bootstrap.init();来进行初始化的,那么具体又做了什么呢?我们看看init()方法是怎么实现的:

/**
     * Initialize daemon.
     */
    public void init()
        throws Exception
    {

        // Set Catalina path
        setCatalinaHome();
        setCatalinaBase();

        initClassLoaders();

        Thread.currentThread().setContextClassLoader(catalinaLoader);

        SecurityClassLoad.securityClassLoad(catalinaLoader);

        // Load our startup class and call its process() method
        if (log.isDebugEnabled())
            log.debug("Loading startup class");
        Class<?> startupClass =
            catalinaLoader.loadClass
            ("org.apache.catalina.startup.Catalina");
        Object startupInstance = startupClass.newInstance();

        // Set the shared extensions class loader
        if (log.isDebugEnabled())
            log.debug("Setting startup class properties");
        String methodName = "setParentClassLoader";
        Class<?> paramTypes[] = new Class[1];
        paramTypes[0] = Class.forName("java.lang.ClassLoader");
        Object paramValues[] = new Object[1];
        paramValues[0] = sharedLoader;
        Method method =
            startupInstance.getClass().getMethod(methodName, paramTypes);
        method.invoke(startupInstance, paramValues);

        catalinaDaemon = startupInstance;

    }


从代码里可以看出,主要做了三件事:

(1)设置了catalina.base和catalina.home路径;

(2)初始化了需要的类加载器;

(3)利用Java中的反射机制,通过执行setParentClassLoader方法来设置Tomcat类加载体系的顶级类加载器;


第二步:调用Bootstrap类的load()来加载server.xml配置文件

我们打开Bootstrap类的load方法,如下所示:

/**
     * Load daemon.
     */
    private void load(String[] arguments)
        throws Exception {

        // Call the load() method
        String methodName = "load";
        Object param[];
        Class<?> paramTypes[];
        if (arguments==null || arguments.length==0) {
            paramTypes = null;
            param = null;
        } else {
            paramTypes = new Class[1];
            paramTypes[0] = arguments.getClass();
            param = new Object[1];
            param[0] = arguments;
        }
        Method method =
            catalinaDaemon.getClass().getMethod(methodName, paramTypes);
        if (log.isDebugEnabled())
            log.debug("Calling startup class " + method);
        method.invoke(catalinaDaemon, param);

    }

从代码可以看出最终还是执行的是org.apache.catalina.startup.Catalina类的load方法,加载server.xml文件,如下所示,至于具体的解析过程我们这里就不详述了,后面讲使用专门的一篇文章进行讲解,如果想知道可以继续关注我的博客或者自己去看源码学习^_^:

/**
     * Start a new server instance.
     */
    public void load() {

        long t1 = System.nanoTime();

        initDirs();

        // Before digester - it may be needed

        initNaming();

        // Create and execute our Digester
        Digester digester = createStartDigester();

        InputSource inputSource = null;
        InputStream inputStream = null;
        File file = null;
        try {
            try {
                file = configFile();
                inputStream = new FileInputStream(file);
                inputSource = new InputSource(file.toURI().toURL().toString());
            } catch (Exception e) {
                if (log.isDebugEnabled()) {
                    log.debug(sm.getString("catalina.configFail", file), e);
                }
            }
            if (inputStream == null) {
                try {
                    inputStream = getClass().getClassLoader()
                        .getResourceAsStream(getConfigFile());
                    inputSource = new InputSource
                        (getClass().getClassLoader()
                         .getResource(getConfigFile()).toString());
                } catch (Exception e) {
                    if (log.isDebugEnabled()) {
                        log.debug(sm.getString("catalina.configFail",
                                getConfigFile()), e);
                    }
                }
            }

            // This should be included in catalina.jar
            // Alternative: don't bother with xml, just create it manually.
            if( inputStream==null ) {
                try {
                    inputStream = getClass().getClassLoader()
                            .getResourceAsStream("server-embed.xml");
                    inputSource = new InputSource
                    (getClass().getClassLoader()
                            .getResource("server-embed.xml").toString());
                } catch (Exception e) {
                    if (log.isDebugEnabled()) {
                        log.debug(sm.getString("catalina.configFail",
                                "server-embed.xml"), e);
                    }
                }
            }


            if (inputStream == null || inputSource == null) {
                if  (file == null) {
                    log.warn(sm.getString("catalina.configFail",
                            getConfigFile() + "] or [server-embed.xml]"));
                } else {
                    log.warn(sm.getString("catalina.configFail",
                            file.getAbsolutePath()));
                    if (file.exists() && !file.canRead()) {
                        log.warn("Permissions incorrect, read permission is not allowed on the file.");
                    }
                }
                return;
            }

            try {
                inputSource.setByteStream(inputStream);
                digester.push(this);
                digester.parse(inputSource);
            } catch (SAXParseException spe) {
                log.warn("Catalina.start using " + getConfigFile() + ": " +
                        spe.getMessage());
                return;
            } catch (Exception e) {
                log.warn("Catalina.start using " + getConfigFile() + ": " , e);
                return;
            }
        } finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException e) {
                    // Ignore
                }
            }
        }

        getServer().setCatalina(this);

        // Stream redirection
        initStreams();

        // Start the new server
        try {
            getServer().init();
        } catch (LifecycleException e) {
            if (Boolean.getBoolean("org.apache.catalina.startup.EXIT_ON_INIT_FAILURE")) {
                throw new java.lang.Error(e);
            } else {
                log.error("Catalina.start", e);
            }

        }

        long t2 = System.nanoTime();
        if(log.isInfoEnabled()) {
            log.info("Initialization processed in " + ((t2 - t1) / 1000000) + " ms");
        }

    }

第三步:调用Bootstrap类的start()方法启动Tomcat

我们打开start()方法的实现,如下所示:

/**
     * Start the Catalina daemon.
     */
    public void start()
        throws Exception {
        if( catalinaDaemon==null ) init();

        Method method = catalinaDaemon.getClass().getMethod("start", (Class [] )null);
        method.invoke(catalinaDaemon, (Object [])null);

    }

从代码看,其实最终执行的是org.apache.catalina.startup.Catalina类的start方法,那么org.apache.catalina.startup.Catalina类的start方法是怎么实现的呢?如下所示:

/**
     * Start a new server instance.
     */
    public void start() {

        if (getServer() == null) {
            load();
        }

        if (getServer() == null) {
            log.fatal("Cannot start server. Server instance is not configured.");
            return;
        }

        long t1 = System.nanoTime();

        // Start the new server
        try {
            getServer().start();
        } catch (LifecycleException e) {
            log.fatal(sm.getString("catalina.serverStartFail"), e);
            try {
                getServer().destroy();
            } catch (LifecycleException e1) {
                log.debug("destroy() failed for failed Server ", e1);
            }
            return;
        }

        long t2 = System.nanoTime();
        if(log.isInfoEnabled()) {
            log.info("Server startup in " + ((t2 - t1) / 1000000) + " ms");
        }

        // Register shutdown hook
        if (useShutdownHook) {
            if (shutdownHook == null) {
                shutdownHook = new CatalinaShutdownHook();
            }
            Runtime.getRuntime().addShutdownHook(shutdownHook);

            // If JULI is being used, disable JULI's shutdown hook since
            // shutdown hooks run in parallel and log messages may be lost
            // if JULI's hook completes before the CatalinaShutdownHook()
            LogManager logManager = LogManager.getLogManager();
            if (logManager instanceof ClassLoaderLogManager) {
                ((ClassLoaderLogManager) logManager).setUseShutdownHook(
                        false);
            }
        }

        if (await) {
            await();
            stop();
        }
    }

从代码看,做了以下工作:

(1)首先是判断Catalina的Server实例是否初始化成功了,如果没有,则继续调用Catalina类的的load方法进行初始化;

(2)初始化成功之后,会调用上面代码中标红部分进行整个组件的启动操作,这里想说的是,由于Tomcat内部设计的问题,整个组件的启动并不是分散的,父级组件的启动会带动子级元素组件的启动,依次类推,会使整个组件都启动起来,例如Server的启动会使相关的Service组件都启动,而Service的启动又会带动Connector的启动等等。这里不做详述,将另起一篇文章单独说明,这篇文章只简单描述整个启动过程框架。

(3)如上述代码中蓝色部分所示,设置了关闭钩子,用于在Tomcat因为各种原因退出时做一些清理工作;

(4)调用Catalina自身类的await方法循环等待shutdown命令;

/**
     * Await and shutdown.
     */
    public void await() {

        getServer().await();

    }

Catalina类的await()方法其实只是代理了Server组件的await()方法。

我们在Eclipse内找到org.apache.catalina.core包下的Server组件的标准实现StandardServer,我们看看它的await方法都做了什么?

/**
     * <span style="color:#FF0000;">Wait until a proper shutdown command is received, then return.</span>
     * This keeps the main thread alive - the thread pool listening for http 
     * connections is daemon threads.
     */
    @Override
    public void await() {
        // Negative values - don't wait on port - tomcat is embedded or we just don't like ports
        if( port == -2 ) {
            // undocumented yet - for embedding apps that are around, alive.
            return;
        }
        if( port==-1 ) {
            try {
                awaitThread = Thread.currentThread();
                while(!stopAwait) {
                    try {
                        Thread.sleep( 10000 );
                    } catch( InterruptedException ex ) {
                        // continue and check the flag
                    }
                }
            } finally {
                awaitThread = null;
            }
            return;
        }

        // Set up a server socket to wait on
        try {
            awaitSocket = new ServerSocket(port, 1,
                    InetAddress.getByName(address));
        } catch (IOException e) {
            log.error("StandardServer.await: create[" + address
                               + ":" + port
                               + "]: ", e);
            return;
        }

        try {
            awaitThread = Thread.currentThread();

            // Loop waiting for a connection and a valid command
            while (!stopAwait) {
                ServerSocket serverSocket = awaitSocket;
                if (serverSocket == null) {
                    break;
                }
    
                // Wait for the next connection
                Socket socket = null;
                StringBuilder command = new StringBuilder();
                try {
                    InputStream stream;
                    long acceptStartTime = System.currentTimeMillis();
                    try {
                        <span style="color:#3333FF;">socket = serverSocket.accept();</span>
                        socket.setSoTimeout(10 * 1000);  // Ten seconds
                        stream = socket.getInputStream();
                    } catch (SocketTimeoutException ste) {
                        // This should never happen but bug 56684 suggests that
                        // it does.
                        log.warn(sm.getString("standardServer.accept.timeout",
                                Long.valueOf(System.currentTimeMillis() - acceptStartTime)), ste);
                        continue;
                    } catch (AccessControlException ace) {
                        log.warn("StandardServer.accept security exception: "
                                + ace.getMessage(), ace);
                        continue;
                    } catch (IOException e) {
                        if (stopAwait) {
                            // Wait was aborted with socket.close()
                            break;
                        }
                        log.error("StandardServer.await: accept: ", e);
                        break;
                    }

                    // Read a set of characters from the socket
                    int expected = 1024; // Cut off to avoid DoS attack
                    while (expected < shutdown.length()) {
                        if (random == null)
                            random = new Random();
                        expected += (random.nextInt() % 1024);
                    }
                    while (expected > 0) {
                        int ch = -1;
                        try {
                            ch = stream.read();
                        } catch (IOException e) {
                            log.warn("StandardServer.await: read: ", e);
                            ch = -1;
                        }
                        if (ch < 32)  // Control character or EOF terminates loop
                            break;
                        command.append((char) ch);
                        expected--;
                    }
                } finally {
                    // Close the socket now that we are done with it
                    try {
                        if (socket != null) {
                            socket.close();
                        }
                    } catch (IOException e) {
                        // Ignore
                    }
                }

                // Match against our command string
                <span style="color:#3366FF;">boolean match = command.toString().equals(shutdown);
                if (match) {
                    log.info(sm.getString("standardServer.shutdownViaPort"));
                    break;
                } else
                    log.warn("StandardServer.await: Invalid command '"
                            + command.toString() + "' received");</span>
            }
        } finally {
            ServerSocket serverSocket = awaitSocket;
            awaitThread = null;
            awaitSocket = null;

            // Close the server socket and return
            if (serverSocket != null) {
                try {
                    serverSocket.close();
                } catch (IOException e) {
                    // Ignore
                }
            }
        }
    }

正如上面标红部分描述的那样,这个方法一直等待socket连接并接受shutdown命令。上述代码中蓝色标记部分用于一直等待Socket连接,并且判断接收到的指令是否是shutdown变量(在类前面定义了shutdown = "SHUTDOWN";这里用的是equals,因此是大小写敏感的,如果写成了小写的“shutdown”也是不行的哦!!!),如果是,则跳出循环,并关闭socket服务;

(5)如果Tomcat正常运行且没有收到shutdown命令,那么程序会一直等待在await()方法处(阻塞在(4)中的serverSocket.accept()),一旦接收到shutdown命令,awaiit()方法会退出循环等待,并执行stop方法。下面看看stop()方法做了什么:

/**
     * Stop an existing server instance.
     */
    public void stop() {

        try {
            // Remove the ShutdownHook first so that server.stop()
            // doesn't get invoked twice
            if (useShutdownHook) {
                Runtime.getRuntime().removeShutdownHook(shutdownHook);

                // If JULI is being used, re-enable JULI's shutdown to ensure
                // log messages are not lost
                LogManager logManager = LogManager.getLogManager();
                if (logManager instanceof ClassLoaderLogManager) {
                    ((ClassLoaderLogManager) logManager).setUseShutdownHook(
                            true);
                }
            }
        } catch (Throwable t) {
            ExceptionUtils.handleThrowable(t);
            // This will fail on JDK 1.2. Ignoring, as Tomcat can run
            // fine without the shutdown hook.
        }

        // Shut down the server
        try {
            Server s = getServer();
            LifecycleState state = s.getState();
            if (LifecycleState.STOPPING_PREP.compareTo(state) <= 0
                    && LifecycleState.DESTROYED.compareTo(state) >= 0) {
                // Nothing to do. stop() was already called
            } else {
                s.stop();
                s.destroy();
            }
        } catch (LifecycleException e) {
            log.error("Catalina.stop", e);
        }

    }

从代码看,首先是在运行时中移除了关闭钩子,然后调用stop方法和destroy()方法分别关闭服务和释放资源。

至此,整个Tomcat的启动过程我们比较详细的进行了说明,至于其中的部分细节并没有详细说明,将另起文章进行单独说明,如类加载器、组件之间如何只要启动一个Server组件就可以全部启动,启动成功之后关闭又是什么样的一个过程等等,如果想知道,可以继续关注我的博客,谢谢。





Tomcat探秘(4):tomcat启动过程详述

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原文地址:http://blog.csdn.net/majinggogogo/article/details/51635511

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