java - 尝试动态实例化类

Question

我正在尝试使用此类与服务器建立连接。此类获取对 HashMap 中的图像执行操作所需的参数列表。然后在 doInBackground 中，我对 Image 进行了一项一项所需的操作。 OVFImage Deployer 类之一的代码也粘贴在下面

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;



}
}

OVFImage Deployer 的代码

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();
    }

}

}

现在，当我运行代码时，我在 ((ChannelExec)channel).setCommand(command) 行上收到 NullPointerException。我知道如果我将 makeAConnection 放在 OVFImageDeployer 中的 try block 之后，代码就会起作用，但我不想一次又一次地建立连接。我希望连接仅初始化一次，并且仅使用该连接执行所有操作。

Answer 1

您应该从 ImageDeployer 的构造函数内部删除对 doInBackground 的调用:

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

这将在您创建 ImageDeployer 实例时初始化 channel 。您可以将 channel 添加到 OVFImageDeployer 的构造函数参数列表中:

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

this.channel = channel;
...
}

这将使用 ImageDeployer 实例中存在的 channel 创建一个 OVFImageDeployer 实例。您需要从 doInBackground 方法内部删除这两条语句，并在构造 OVFImageDeployer 实例时传递 channel 以及其他参数:

@Override
protected Boolean doInBackground() throws Exception {

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

现在客户端代码可以创建 ImageDeployer 的实例并可以在其上执行 doInBackground:

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

这样，每次在 doInBackground 方法内创建 OVFImageDeployer 实例时，您都可以在构造 ImageDeployer 实例时使用由 makeAConnection 方法创建的相同 channel。