深入理解Tomcat（四）Pipeline和Valve

前言

在上一小節(jié)我們簡單分析了一下Pipeline和Valve，并給出了整體的結(jié)構(gòu)圖。而這一節(jié)，我們將詳細(xì)分析Tomcat里面的源碼。

pipeline+valve

Valve

Valve作為一個個基礎(chǔ)的閥門，扮演著業(yè)務(wù)實(shí)際執(zhí)行者的角色。我們看看Valve這個接口有哪些方法。

public interface Valve {
    // 獲取下一個閥門
    public Valve getNext();
    // 設(shè)置下一個閥門
    public void setNext(Valve valve);
    // 后臺執(zhí)行邏輯，主要在類加載上下文中使用到
    public void backgroundProcess();
    // 執(zhí)行業(yè)務(wù)邏輯
    public void invoke(Request request, Response response)
        throws IOException, ServletException;
    // 是否異步執(zhí)行
    public boolean isAsyncSupported();
}

Contained

ValveBase、Pipeline及其他相關(guān)組件都實(shí)現(xiàn)了Contained接口，我們看看這個接口有哪些方法。很簡單，就是get/set容器操作。

public interface Contained {

    /**
     * Get the {@link Container} with which this instance is associated.
     *
     * @return The Container with which this instance is associated or
     *         <code>null</code> if not associated with a Container
     */
    Container getContainer();


    /**
     * Set the <code>Container</code> with which this instance is associated.
     *
     * @param container The Container instance with which this instance is to
     *  be associated, or <code>null</code> to disassociate this instance
     *  from any Container
     */
    void setContainer(Container container);
}

ValveBase

從Valve的類層次結(jié)構(gòu)，我們發(fā)現(xiàn)幾乎所有Valve都繼承了ValveBase這個抽象類，所以這兒我們需要分析一下它。

Valve類層次結(jié)構(gòu)
public abstract class ValveBase extends LifecycleMBeanBase implements Contained, Valve {
    // 國際化管理器，可以支持多國語言
    protected static final StringManager sm = StringManager.getManager(ValveBase.class);

    //------------------------------------------------------ Instance Variables

    // 無參構(gòu)造方法，默認(rèn)不支持異步
    public ValveBase() {
        this(false);
    }
    // 有參構(gòu)造方法，可傳入異步支持標(biāo)記
    public ValveBase(boolean asyncSupported) {
        this.asyncSupported = asyncSupported;
    }


    //------------------------------------------------------ Instance Variables

    // 異步標(biāo)記
    protected boolean asyncSupported;
    // 所屬容器
    protected Container container = null;
    // 容器日志組件對象
    protected Log containerLog = null;
    // 下一個閥門
    protected Valve next = null;


    //-------------------------------------------------------------- Properties

    // 獲取所屬容器
    @Override
    public Container getContainer() {
        return container;
    }
    // 設(shè)置所屬容器
    @Override
    public void setContainer(Container container) {
        this.container = container;
    }
    // 是否異步執(zhí)行
    @Override
    public boolean isAsyncSupported() {
        return asyncSupported;
    }
    // 設(shè)置是否異步執(zhí)行
    public void setAsyncSupported(boolean asyncSupported) {
        this.asyncSupported = asyncSupported;
    }
    // 獲取下一個待執(zhí)行的閥門
    @Override
    public Valve getNext() {
        return next;
    }
    // 設(shè)置下一個待執(zhí)行的閥門
    @Override
    public void setNext(Valve valve) {
        this.next = valve;
    }


    //---------------------------------------------------------- Public Methods

    // 后臺執(zhí)行，子類實(shí)現(xiàn)
    @Override
    public void backgroundProcess() {
        // NOOP by default
    }
    // 初始化邏輯
    @Override
    protected void initInternal() throws LifecycleException {
        super.initInternal();
        // 設(shè)置容器日志組件對象到當(dāng)前閥門的containerLog屬性
        containerLog = getContainer().getLogger();
    }
    // 啟動邏輯
    @Override
    protected synchronized void startInternal() throws LifecycleException {
        setState(LifecycleState.STARTING);
    }
    // 停止邏輯
    @Override
    protected synchronized void stopInternal() throws LifecycleException {
        setState(LifecycleState.STOPPING);
    }
    // 重寫toString，格式為[${containerName}]
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder(this.getClass().getName());
        sb.append('[');
        if (container == null) {
            sb.append("Container is null");
        } else {
            sb.append(container.getName());
        }
        sb.append(']');
        return sb.toString();
    }


    // -------------------- JMX and Registration  --------------------

    // 設(shè)置獲取MBean對象的keyProperties，格式如：a=b,c=d,e=f...
    @Override
    public String getObjectNameKeyProperties() {
        StringBuilder name = new StringBuilder("type=Valve");

        Container container = getContainer();

        name.append(container.getMBeanKeyProperties());

        int seq = 0;

        // Pipeline may not be present in unit testing
        Pipeline p = container.getPipeline();
        if (p != null) {
            for (Valve valve : p.getValves()) {
                // Skip null valves
                if (valve == null) {
                    continue;
                }
                // Only compare valves in pipeline until we find this valve
                if (valve == this) {
                    break;
                }
                if (valve.getClass() == this.getClass()) {
                    // Duplicate valve earlier in pipeline
                    // increment sequence number
                    seq ++;
                }
            }
        }

        if (seq > 0) {
            name.append(",seq=");
            name.append(seq);
        }

        String className = this.getClass().getName();
        int period = className.lastIndexOf('.');
        if (period >= 0) {
            className = className.substring(period + 1);
        }
        name.append(",name=");
        name.append(className);

        return name.toString();
    }
    // 獲取所屬域，從container獲取
    @Override
    public String getDomainInternal() {
        Container c = getContainer();
        if (c == null) {
            return null;
        } else {
            return c.getDomain();
        }
    }
}

Pipeline

Pipeline作為一個管道，我們可以簡單認(rèn)為是一個Valve的集合，內(nèi)部會對這個集合進(jìn)行遍歷，調(diào)用每個元素的業(yè)務(wù)邏輯方法invoke()。

是不是這樣呢？我們還是分析一下源碼，先看看接口定義。

public interface Pipeline {
    // ------------------------------------------------------------- Properties

    // 獲取基本閥門
    public Valve getBasic();
    // 設(shè)置基本閥門
    public void setBasic(Valve valve);

    // --------------------------------------------------------- Public Methods

    // 添加閥門
    public void addValve(Valve valve);
    // 獲取閥門數(shù)組
    public Valve[] getValves();
    // 刪除閥門
    public void removeValve(Valve valve);
    // 獲取首個閥門
    public Valve getFirst();
    // 管道內(nèi)所有閥門是否異步執(zhí)行
    public boolean isAsyncSupported();
    // 獲取管道所屬的容器
    public Container getContainer();
    // 設(shè)置管道所屬的容器
    public void setContainer(Container container);
    // 查找非異步執(zhí)行的所有閥門，并放置到result參數(shù)中，所以result不允許為null
    public void findNonAsyncValves(Set<String> result);
}

StandardPipeline

接著我們分析一下Pipeline唯一的實(shí)現(xiàn)StandardPipeline。代碼很長，但是都很簡單。

public class StandardPipeline extends LifecycleBase
        implements Pipeline, Contained {

    private static final Log log = LogFactory.getLog(StandardPipeline.class);

    // ----------------------------------------------------------- Constructors

    // 構(gòu)造一個沒有所屬容器的管道
    public StandardPipeline() {
        this(null);
    }

    // 構(gòu)造一個有所屬容器的管道
    public StandardPipeline(Container container) {
        super();
        setContainer(container);
    }

    // ----------------------------------------------------- Instance Variables

    /**
     * 基本閥門，最后執(zhí)行的閥門
     */
    protected Valve basic = null;

    /**
     * 管道所屬的容器
     */
    protected Container container = null;

    /**
     * 管道里面的首個執(zhí)行的閥門
     */
    protected Valve first = null;

    // --------------------------------------------------------- Public Methods

    // 是否異步執(zhí)行，如果一個閥門都沒有，或者所有閥門都是異步執(zhí)行的，才返回true
    @Override
    public boolean isAsyncSupported() {
        Valve valve = (first!=null)?first:basic;
        boolean supported = true;
        while (supported && valve!=null) {
            supported = supported & valve.isAsyncSupported();
            valve = valve.getNext();
        }
        return supported;
    }

    // 查找所有未異步執(zhí)行的閥門
    @Override
    public void findNonAsyncValves(Set<String> result) {
        Valve valve = (first!=null) ? first : basic;
        while (valve != null) {
            if (!valve.isAsyncSupported()) {
                result.add(valve.getClass().getName());
            }
            valve = valve.getNext();
        }
    }

    // ------------------------------------------------------ Contained Methods

    // 獲取所屬容器
    @Override
    public Container getContainer() {
        return (this.container);
    }

    // 設(shè)置所屬容器
    @Override
    public void setContainer(Container container) {
        this.container = container;
    }

    // 初始化邏輯，默認(rèn)沒有任何邏輯
    @Override
    protected void initInternal() {
        // NOOP
    }

    // 開始邏輯，調(diào)用所有閥門的start方法
    @Override
    protected synchronized void startInternal() throws LifecycleException {
        // Start the Valves in our pipeline (including the basic), if any
        Valve current = first;
        if (current == null) {
            current = basic;
        }
        while (current != null) {
            if (current instanceof Lifecycle)
                ((Lifecycle) current).start();
            current = current.getNext();
        }

        setState(LifecycleState.STARTING);
    }

    // 停止邏輯，調(diào)用所有閥門的stop方法
    @Override
    protected synchronized void stopInternal() throws LifecycleException {
        setState(LifecycleState.STOPPING);

        // Stop the Valves in our pipeline (including the basic), if any
        Valve current = first;
        if (current == null) {
            current = basic;
        }
        while (current != null) {
            if (current instanceof Lifecycle)
                ((Lifecycle) current).stop();
            current = current.getNext();
        }
    }

    // 銷毀邏輯，移掉所有閥門，調(diào)用removeValve方法
    @Override
    protected void destroyInternal() {
        Valve[] valves = getValves();
        for (Valve valve : valves) {
            removeValve(valve);
        }
    }

    /**
     * 重新toString方法
     */
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder("Pipeline[");
        sb.append(container);
        sb.append(']');
        return sb.toString();
    }

    // ------------------------------------------------------- Pipeline Methods

    // 獲取基礎(chǔ)閥門
    @Override
    public Valve getBasic() {
        return (this.basic);
    }

    // 設(shè)置基礎(chǔ)閥門
    @Override
    public void setBasic(Valve valve) {
        // Change components if necessary
        Valve oldBasic = this.basic;
        if (oldBasic == valve)
            return;

        // Stop the old component if necessary
        // 老的基礎(chǔ)閥門會被調(diào)用stop方法且所屬容器置為null
        if (oldBasic != null) {
            if (getState().isAvailable() && (oldBasic instanceof Lifecycle)) {
                try {
                    ((Lifecycle) oldBasic).stop();
                } catch (LifecycleException e) {
                    log.error("StandardPipeline.setBasic: stop", e);
                }
            }
            if (oldBasic instanceof Contained) {
                try {
                    ((Contained) oldBasic).setContainer(null);
                } catch (Throwable t) {
                    ExceptionUtils.handleThrowable(t);
                }
            }
        }

        // Start the new component if necessary
        // 新的閥門會設(shè)置所屬容器，并調(diào)用start方法
        if (valve == null)
            return;
        if (valve instanceof Contained) {
            ((Contained) valve).setContainer(this.container);
        }
        if (getState().isAvailable() && valve instanceof Lifecycle) {
            try {
                ((Lifecycle) valve).start();
            } catch (LifecycleException e) {
                log.error("StandardPipeline.setBasic: start", e);
                return;
            }
        }

        // Update the pipeline
        // 替換pipeline中的基礎(chǔ)閥門，就是講基礎(chǔ)閥門的前一個閥門的next指向當(dāng)前閥門
        Valve current = first;
        while (current != null) {
            if (current.getNext() == oldBasic) {
                current.setNext(valve);
                break;
            }
            current = current.getNext();
        }

        this.basic = valve;
    }

    // 添加閥門
    @Override
    public void addValve(Valve valve) {
        // Validate that we can add this Valve
        // 設(shè)置所屬容器
        if (valve instanceof Contained)
            ((Contained) valve).setContainer(this.container);

        // Start the new component if necessary
        // 調(diào)用閥門的start方法
        if (getState().isAvailable()) {
            if (valve instanceof Lifecycle) {
                try {
                    ((Lifecycle) valve).start();
                } catch (LifecycleException e) {
                    log.error("StandardPipeline.addValve: start: ", e);
                }
            }
        }

        // Add this Valve to the set associated with this Pipeline
        // 設(shè)置閥門，將閥門添加到基礎(chǔ)閥門的前一個
        if (first == null) {
            first = valve;
            valve.setNext(basic);
        } else {
            Valve current = first;
            while (current != null) {
                if (current.getNext() == basic) {
                    current.setNext(valve);
                    valve.setNext(basic);
                    break;
                }
                current = current.getNext();
            }
        }

        container.fireContainerEvent(Container.ADD_VALVE_EVENT, valve);
    }

    // 獲取閥門數(shù)組
    @Override
    public Valve[] getValves() {
        ArrayList<Valve> valveList = new ArrayList<>();
        Valve current = first;
        if (current == null) {
            current = basic;
        }
        while (current != null) {
            valveList.add(current);
            current = current.getNext();
        }

        return valveList.toArray(new Valve[0]);
    }

    // JMX方法，在此忽略
    public ObjectName[] getValveObjectNames() {
        ArrayList<ObjectName> valveList = new ArrayList<>();
        Valve current = first;
        if (current == null) {
            current = basic;
        }
        while (current != null) {
            if (current instanceof JmxEnabled) {
                valveList.add(((JmxEnabled) current).getObjectName());
            }
            current = current.getNext();
        }

        return valveList.toArray(new ObjectName[0]);
    }

    // 移除閥門
    @Override
    public void removeValve(Valve valve) {
        Valve current;
        if(first == valve) {
            // 如果待移出的閥門是首個閥門，則首個閥門的下一個閥門變成首個閥門
            first = first.getNext();
            current = null;
        } else {
            current = first;
        }
        // 遍歷閥門集合，并進(jìn)行移除
        while (current != null) {
            if (current.getNext() == valve) {
                current.setNext(valve.getNext());
                break;
            }
            current = current.getNext();
        }

        if (first == basic) first = null;

        // 設(shè)置閥門所屬容器為null
        if (valve instanceof Contained)
            ((Contained) valve).setContainer(null);

        // 調(diào)用待移除閥門的stop方法和destroy方法，并觸發(fā)移除閥門事件
        if (valve instanceof Lifecycle) {
            // Stop this valve if necessary
            if (getState().isAvailable()) {
                try {
                    ((Lifecycle) valve).stop();
                } catch (LifecycleException e) {
                    log.error("StandardPipeline.removeValve: stop: ", e);
                }
            }
            try {
                ((Lifecycle) valve).destroy();
            } catch (LifecycleException e) {
                log.error("StandardPipeline.removeValve: destroy: ", e);
            }
        }

        container.fireContainerEvent(Container.REMOVE_VALVE_EVENT, valve);
    }

    // 獲取首個閥門，如果閥門列表為null，返回基礎(chǔ)閥門
    @Override
    public Valve getFirst() {
        if (first != null) {
            return first;
        }
        return basic;
    }
}

總結(jié)

通過上面的代碼分析，我們發(fā)現(xiàn)了幾個關(guān)鍵的設(shè)計模式：

  1. 模板方法模式，父類定義框架，子類實(shí)現(xiàn)
  2. 責(zé)任鏈模式，就是這兒的管道/閥門的實(shí)現(xiàn)方式，每個閥門維護(hù)一個next屬性指向下一個閥門

分析之初，我們還以為很復(fù)雜。分析之后，我們卻發(fā)現(xiàn)，高級的東西并不一定復(fù)雜，反而簡單易懂。或許這就是高級開發(fā)比中低級開發(fā)更理解軟件開發(fā)的含義吧~

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