1. JCoContext

如果SAP中多个函数需要在一个session中运行，需要JCoContext来提供保证。如果在同一个线程中，大体模式这样：

JCoContext.begin(sapDestination);

fm1.execute(sapDestination);
fm2.execute(sapDestination);

JCoContext.end(destination);

begin()和end()之间的函数execute之后，SAP不会释放连接，确保同一个session之中。

第二种情况：如果不同的函数不在同一个线程中，需要由开发人员实现SessionReferenceProvider接口，在类中提供session id。逻辑跟nco3.0也是一样的。JCo3.0提供了一个示例代码，但是搞的太复杂，我弄了一个简单的，方便理解。

2. SAP函数

我们要使用的函数是从标准系统函数INCREMENT_COUNTER
，GET_COUNTER拷贝而来的。在SAP系统中INCREMENT_COUNTER
，GET_COUNTER在同一个function group中，共享一个变量count（计数器），每次运行INCREMENT_COUNTER
, count就会加一，GET_COUNTER函数
可以获得这个count。因为这两个函数不能被远程调用，所以我们将这两个函数拷贝出另外两个函数ZINCREMENT_COUNTER和ZGET_COUNTER。

3. 同一线程中执行函数

首先我们把两个函数定义在一个类RfcFunctions中：

package jco3.demo6;

import com.sap.conn.jco.JCoDestination;
import com.sap.conn.jco.JCoException;
import com.sap.conn.jco.JCoFunction;

public class RfcFunctions
{
    public static int runGetCounter(JCoDestination dest) throws JCoException
    {
        JCoFunction counterFM = dest.getRepository().getFunction("ZGET_COUNTER");
        counterFM.execute(dest);
        int counter = (int) counterFM.getExportParameterList().getValue("GET_VALUE");

        return counter;        
    }

    public static void runIncrement(JCoDestination dest) throws JCoException
    {
        JCoFunction increment = dest.getRepository().getFunction("ZINCREMENT_COUNTER");
        increment.execute(dest);        
    }
}

然后编写测试类进行测试：

package jco3.demo6;

import com.sap.conn.jco.JCoContext;
import com.sap.conn.jco.JCoDestination;
import com.sap.conn.jco.JCoDestinationManager;
import com.sap.conn.jco.JCoException;

public class TestSessionSameThread
{
    public static void main(String[] args) throws JCoException, InterruptedException
    {        
        // get JCoDestination object instance
        JCoDestination destination = JCoDestinationManager.getDestination("ECC");

        // make sure the two functions will be executed in the same session
        JCoContext.begin(destination);

        // Before increment
        System.out.println("Before execution of ZINCREMENT_COUNTER:");
        System.out.println("Counter:" + RfcFunctions.runGetCounter(destination));

        // Run incrementCounter five times
        for(int i = 0; i < 5; i++){
            RfcFunctions.runIncrement(destination);
            System.out.println("Add:" + (i + 1));
        }

        // After increment    
        System.out.println("After execution of ZINCREMENT_COUNTER:");
        System.out.println("Counter:" + RfcFunctions.runGetCounter(destination));    

        // release the connection 
        JCoContext.end(destination);
    }
}

代码很直观，就不多说了。函数执行前，counter的值为0，运行函数5次之后，counter的值为5。如果我们注释掉JCoContext.begin(destination);和JCoContext.end(destination);，可以对比出不同的效果。

4. 不同线程中执行函数

如果在不同的线程中执行不同的函数，需要开发者提供session id。我准备将两个函数放在不同的线程中：

在JVM的主线程中调用ZGET_COUNTER，查看counter的结果。
在另外一个线程中运行ZINCREMENT_COUNTER，两个线程通过JCoContext，保持在同一个session ID下。

4.1 实现JCoSessionReference接口

JCoSessionRefence实现类的主要作用是提供session ID:

package jco3.session;

import java.util.concurrent.atomic.AtomicInteger;
import com.sap.conn.jco.ext.JCoSessionReference;

public class JCoSessionRefenceImpl implements JCoSessionReference
{
    private AtomicInteger atomInt = new AtomicInteger(0);
    private String id = "session"+String.valueOf(atomInt.addAndGet(1));

    public void contextFinished()
    {        
    }

    public void contextStarted()
    {    
    }

    @Override
    public String getID()
    {
        /**
         * We need to override getID() method
         */

        return id;
    }
}

4.2 实现SessionReferenceProvider接口

在SessionReferenceProvider接口的实现类中，改写getCurrentSessionReference()方法，获取上面定义的JCoSessionRefence，从而获得session ID。其他方法保持不动。

package jco3.session;

import com.sap.conn.jco.ext.JCoSessionReference;
import com.sap.conn.jco.ext.SessionException;
import com.sap.conn.jco.ext.SessionReferenceProvider;

public class SessionReferencProviderImpl implements SessionReferenceProvider
{

    @Override
    public JCoSessionReference getCurrentSessionReference(String scopeType)
    {
        /**
         *  We need to override getCurrentSessionReference() method
         */

        JCoSessionRefenceImpl sessionRef = new JCoSessionRefenceImpl();
        return sessionRef;
    }

    @Override
    public boolean isSessionAlive(String sessionID)
    {
        return false;
    }

    public void jcoServerSessionContinued(String sessionID) throws SessionException
    {        
    }

    public void jcoServerSessionFinished(String sessionID)
    {        
    }

    public void jcoServerSessionPassivated(String sessionID) throws SessionException
    {        
    }

    public JCoSessionReference jcoServerSessionStarted() throws SessionException
    {
        return null;
    }
}

4.3 注册 SessionReferenceProvider接口

package jco3.session;

import com.sap.conn.jco.JCoDestination;
import com.sap.conn.jco.JCoDestinationManager;
import com.sap.conn.jco.JCoException;
import com.sap.conn.jco.ext.Environment;
import com.sap.conn.jco.ext.SessionReferenceProvider;

public class DestinationProvider
{
    public static JCoDestination getDestination() throws JCoException
    {
        // create an instance of SessionReferenceProvider
        // and register in environment
        SessionReferenceProvider provider = new SessionReferencProviderImpl();
        Environment.registerSessionReferenceProvider(provider);

        JCoDestination destination = JCoDestinationManager.getDestination("ECC");

        return destination;
    }
}

4.4 在单独线程中执行ZINCREMENT_COUNTER

定义WorkingThread, 从Thread类继承，在这个线程中执行函数ZINCREMENT_COUNTER 5次。

package jco3.demo6;

import com.sap.conn.jco.JCoDestination;
import com.sap.conn.jco.JCoException;

public class WorkingThread extends Thread
{
    private boolean doneSignal;
    private JCoDestination destination;

    // constructor
    public WorkingThread(JCoDestination destination, boolean doneSignal)
    {
        this.destination = destination;
        this.doneSignal = doneSignal;
    }

    public boolean hasDone()
    {
        return doneSignal;
    }

    @Override
    public void run()
    {
        /**
         * run method of runIncrement() for five times
         */

        for (int i = 0; i < 5; i++){
            try {
                RfcFunctions.runIncrement(this.destination);    
                System.out.println("Run " + (i+1) + " times.");
            } catch (JCoException e) {                
                e.printStackTrace();
            }
        }

        this.doneSignal = true;
    }    
}

doneSignal用于标识该线程是否结束。线程本身结束，是run()方法运行完毕。

4.5 测试多线程函数调用

好了，最后来测试在多线程中函数调用：

package jco3.demo6;

import com.sap.conn.jco.JCoContext;
import com.sap.conn.jco.JCoDestination;
import com.sap.conn.jco.JCoException;
import jco3.session.DestinationProvider;

public class TestSAPSessionMultiThread
{    
    public static void main(String[] args) throws JCoException, InterruptedException
    {
        /**
         * Run ZINCREMENT_COUNTER & ZGET_COUNTER functions in
         * different threads in a stateful way.
         * 
         * The SAP will keep a session id which was created in
         * JCoSessionReferenceImpl class 
         * and used in SessionReferenceProviderImpl class.
         * 
         * Before using, SessionReferenceProviderImpl class should be
         * registered using Environment.registerSessionReferenceProvider() method.
         */

        // get JCoDestination object instance
        JCoDestination destination = DestinationProvider.getDestination();

        // make sure the two functions will be executed in the same session
        JCoContext.begin(destination);

        // Before increment
        System.out.println("Before execution of ZINCREMENT_COUNTER:");
        System.out.println("Counter:" + RfcFunctions.runGetCounter(destination));

        // start a new Thread in which function ZINCREMENT_COUNTER
        // will be executed for five times
        WorkingThread workingThread = new WorkingThread(destination, false);
        workingThread.start();

        // wait and switch thread
        Thread.sleep(1000);

        // After increment
        if (workingThread.hasDone() == true){
            System.out.println("After execution of ZINCREMENT_COUNTER:");
            System.out.println("Counter:" + RfcFunctions.runGetCounter(destination));    
        }

        // release the connection 
        JCoContext.end(destination);
    }
}

与前面同一个线程中代码的主要区别是：
定义一个WorkingThread类的实例，然后启动线程：

WorkingThread workingThread = new WorkingThread(destination, false);
workingThread.start();

然后通过Thread.sleep(), 将线程切换到workingThread中执行，执行完毕再回到主线程显示结果。

文／StoneWM（简书作者）
原文链接：http://www.jianshu.com/p/2ce28196483c
著作权归作者所有，转载请联系作者获得授权，并标注“简书作者”。

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