試圖動態地實例化類

Question

我想與使用此類的服務器進行連接。該類獲取在HashMap中對圖像執行操作所需的參數列表。然後在doInBackground中，我逐個執行Image上所需的操作。對於這OVFImage部署中的一個類的代碼粘貼也低於

public class ImageDeployer extends SwingWorker<Boolean,String> { 


    public ImageDeployer(){ 

    } 

    public ImageDeployer(HashMap<String, String> volIDMap, HashMap<String, String> osMap) { 
    // TODO Auto-generated constructor stub 
    this.volIDMap = volIDMap; 
    this.osMap = osMap; 
    System.out.println(volIDMap); 
    System.out.println(osMap); 
    makeAConnection(); 
    try { 
     doInBackground(); 
     System.out.println("Do In Background"); 
    } catch (Exception e) { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } 
} 


public void makeAConnection(){ 

    inputFile = RESTEngine.getFilePath(); 
    Properties defaultProps = new Properties(); 
    try { 
     fin = new FileInputStream(inputFile); 
     defaultProps.load(fin); 
     fin.close(); 
    } 
    catch(FileNotFoundException e1){ 
     System.out.println("The properties file supposed to contain Authorization parameters was not found."); 
     e1.printStackTrace(); 
     System.exit(-1); 
    } 
    catch(IOException e1){ 
     System.out.println("An exception occured while trying to open the properties file"); 
     e1.printStackTrace(); 
     System.exit(-1); 
    } 
    // assign variables from Input file with default value as null 
    user = defaultProps.getProperty("UserID", null); 
    host = defaultProps.getProperty("PowerVC_IP_ADDRESS", null); 
    password = defaultProps.getProperty("UserPass" ,null); 

    jsch = new JSch(); 
    try { 
     session = jsch.getSession(user, host, 22); 
     session.setPassword(password); 
     java.util.Properties config = new java.util.Properties(); 
     config.put("StrictHostKeyChecking", "no"); 
     session.setConfig(config); 
     session.connect(); 
     channel=session.openChannel("exec"); 
     channel.setInputStream(null); 

     try { 
      in = channel.getInputStream(); 
     } catch (IOException e) { 
      // TODO Auto-generated catch block 
      e.printStackTrace(); 
     } 

     System.out.println("Connection Successful"); 
    } catch (JSchException e) { 
     // TODO Auto-generated catch block 
     System.out.println("Unable to connect"); 
     e.printStackTrace(); 
    } 

} 


@Override 
protected Boolean doInBackground() throws Exception { 

    ImageDeployer imageDeployer = new ImageDeployer(); 
    imageDeployer.makeAConnection(); 

    for(String imageName : volIDMap.keySet()){ 

     String volID = volIDMap.get(imageName); 
     String oS = osMap.get(imageName); 
     if (oS.equalsIgnoreCase("aix")){ 

      imageDeployer = new OVFImageDeployer(volID, oS, imageName); 

     } 
     // Other Cases depending upon the OS Type 


    } 
    return null; 



} 
} 

代碼爲OVFImage部署

public class OVFImageDeployer extends PowerVCImageDeployer { 

public OVFImageDeployer(String VolID,String oS,String imageName){ 

    String command="/usr/bin/powervc-devtools/powervc-devcli glance image-create json "+imageName+" "+oS+" "+VolID; 

    try { 


     ((ChannelExec)channel).setCommand(command); 
     channel.connect(); 
    } catch (JSchException e) { 
     // TODO Auto-generated catch block 
     e.printStackTrace(); 
    } 

} 

} 

現在，當我運行代碼我得到的線((ChannelExec)channel).setCommand(command)一個NullPointerException。 我知道如果我在OVFImageDeployer的try塊後面加上makeAConnection這段代碼就可以工作，但是我不想一次又一次地建立連接。我想要一個連接初始化一次，所有的操作只能使用該連接來執行。

Answer 1

你應該從ImageDeployer在構造函數中刪除調用doInBackground：

public ImageDeployer(HashMap<String, String> volIDMap, HashMap<String, String> osMap) { 
    .... 
    makeAConnection(); 
    //doInBackground(); 
    ... 
} 

當您創建的ImageDeployer一個實例這將初始化channel。您可以添加到channel的OVFImageDeployer構造函數的參數列表：

public OVFImageDeployer(String VolID,String oS,String imageName, Channel channel){ 

this.channel = channel; 
... 
} 

這將創建OVFImageDeployer實例與channel是存在於ImageDeployer實例。你需要從doInBackground方法中刪除這兩個語句，並通過channel與其他參數而構建的OVFImageDeployer一個實例：

@Override 
protected Boolean doInBackground() throws Exception { 

//ImageDeployer imageDeployer = new ImageDeployer(); 
//imageDeployer.makeAConnection(); 
... 
ImageDeployer imageDeployer = new OVFImageDeployer(volID, oS, imageName, channel); 
... 
} 

現在客戶端代碼可以創建ImageDeployer一個實例，並且可以在其上執行doInBackground ：

ImageDeployer imageDeployer = new ImageDeployer(); 
imageDeployer.doInBackground(); 

有了這個，你每次創建doInBackground方法內部的OVFImageDeployer實例時，你可以使用由創建的相同channelmakeAConnection方法，同時構造ImageDeployer實例。