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Question

我有一个要求，例如在拨打http电话后必须每隔45分钟更新一次值。

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.List;

import org.apache.http.NameValuePair;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ObjectNode;

public class TokenManagerRunnable implements Runnable{
    
    String token;

    
    public String fetchToken() {
        return this.token;
    }
    

    @Override
    public void run() {
        
        String result = "";
        
        HttpPost post = new HttpPost("https://login.microsoftonline.com/{{TenentId}}/oauth2/token");
        List<NameValuePair> urlParameters = new ArrayList<>();
        urlParameters.add(new BasicNameValuePair("grant_type", "client_credentials"));
        urlParameters.add(new BasicNameValuePair("client_id", "some client id"));
        urlParameters.add(new BasicNameValuePair("client_secret", "some secret id"));
        urlParameters.add(new BasicNameValuePair("resource", "https://database.windows.net"));

        try {
            post.setEntity(new UrlEncodedFormEntity(urlParameters));
        } catch (UnsupportedEncodingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        try (CloseableHttpClient httpClient = HttpClients.createDefault();
             CloseableHttpResponse response = httpClient.execute(post)){

            result = EntityUtils.toString(response.getEntity());
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        
        ObjectNode node;
        try {
            node = new ObjectMapper().readValue(result, ObjectNode.class);
        
        
        System.out.println(result);
        
        if (node.has("access_token")) {
            result = node.get("access_token").toString();           
        }
        System.out.println(result);
        System.out.println(result.substring(1, result.length()-1));
        
        
        //updating the token
        this.token = result.substring(1, result.length()-1);
        
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

这是我的主要功能

        SQLServerDataSource ds = new SQLServerDataSource();
        TokenManagerRunnable tokenManagerRunnable = new TokenManagerRunnable();
        ScheduledExecutorService sches = Executors.newScheduledThreadPool(1);
        sches.scheduleWithFixedDelay(tokenManagerRunnable, 0, 45, TimeUnit.MINUTES);
        System.out.println("fetching the token ---- "+tokenManagerRunnable.fetchToken());
        ds.setAccessToken(tokenManagerRunnable.fetchToken());
       try {
        
        Connection connection = ds.getConnection(); 
        Statement stmt = connection.createStatement();
        ResultSet rs = stmt.executeQuery(" select * from [dbo].[CLIENT]"); 
        System.out.println("You have successfully logged in");
           
        while(rs.next()) {
            System.out.println(rs.getString(1));
        }
        
    }catch(Exception ex) {
        ex.printStackTrace();
    }

tokenManagerRunnable.fetchToken（）带空值，因为尚未执行TokenManagerRunnable类。

如何才能等到ScheduledExecutorService完成任务，这样才能每隔45分钟从tokenManagerRunnable.fetchToken（）获取值并在Datasource中设置新值，而不是null？

有什么想法吗？

Answer 1

这是您已经知道的同步问题。主要有两种同步线程的方法：

使用连接同步
使用回调异步。

从重复性任务的异步特性出发，我想说最好的选择是使用回调。这样，您可以在每次检索新令牌时设置它。

我在下面更新了您的代码：

// Imports [...]

public class TokenManagerRunnable implements Runnable {
    private final SQLServerDataSource ds;

    /**
     * New constructor taking a datasource to trigger the persistence of the token
     * on retrieval.
     * @param ds
     */
    public TokenManagerRunnable(SQLServerDataSource ds) {
        this.ds = ds;
    }

    /**
     * New method persisting the token on datasource when retrieved.
     * @param token
     */
    private void setToken(String token) {
        System.out.println("fetching the token ---- " + token);
        this.ds.setAccessToken(token);
    }

    @Override
    public void run() {
        // Retrieval [...]
        try {
            // Parsing [...]
            //updating the token
            this.setToken(result.substring(1, result.length() - 1));

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

如您所见，在Runner上不需要任何状态，因为它将直接将结果流式传输到数据源。您只需将此数据源提供给正在施工的跑步者。

SQLServerDataSource ds = new SQLServerDataSource();
TokenManagerRunnable tokenManagerRunnable = new TokenManagerRunnable(ds);

// Run 1 time synchronously, at the end of this run call
// the token will be set
tokenManagerRunnable.run();
        
// Schedule a token refresh every 45 minutes starting now
ScheduledExecutorService sches = Executors.newScheduledThreadPool(1);
sches.scheduleWithFixedDelay(tokenManagerRunnable, 0, 45, TimeUnit.MINUTES);

// Use the token [...]

编辑

如评论中所述，您需要先执行Runnable，然后才能联系数据库。您需要同步执行此操作，或者根据您打算对应用程序执行的操作在单独的线程中添加以下代码。问题是您的应用程序是否依赖于此初始化？。

事实上，您可以在不将其放入线程的情况下调用run()方法，这将简单地同步运行令牌更新。这意味着您需要在计划的线程执行中开始自动刷新之前，同步调用tokenManagerRunnable.run();。

Answer 2

如果我的回答正确，您可以使用CompletableFuture。您将token包装在CompletableFuture中，然后调度线程完成了它。由于CompletableFuture是Future，因此其他线程可以在其上等待结果。

这是说明该机制的基本实现。

import java.util.concurrent.CompletableFuture;

class Main {
    
    static CompletableFuture<String> token = new CompletableFuture<>();
    
    
    public static void main(String[] args) {
        new Thread(() -> {
            for (int i = 0; i < 100_000_000; i++) {
                Math.log(Math.sqrt(i));
                if (i % 10_000_000 == 0) {
                    System.out.println("doing stuff");
                }
            }
            token.complete("result");
        }).start();
        
        String result = token.join(); // wait until token is set and get it
        System.out.println("got " + result);
    }
}

请记住，获得结果后，您必须为token分配一个新的CompletableFuture。那是因为它们只能完成一次。

Answer 3

我能够使用以下代码来实现

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ObjectNode;
import com.microsoft.sqlserver.jdbc.SQLServerDataSource;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.http.NameValuePair;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;
 
import java.util.ArrayList;
import java.util.List;
 
public class AzureServicePrincipleTokenManager implements Runnable {
 
 
    SQLServerDataSource ds ;
    String secret;
    String clientId;
    String tenetId;
    static final String RESOURCE = "https://database.windows.net";
    static final String ENDPOINT = "https://login.microsoftonline.com/";
    static final String GRANT_TYPE = "client_credentials";
    boolean confirmTokenFlag=false;
    private static Log logger = LogFactory.getLog( "AzureServicePrincipleTokenManager" );
 
    public AzureServicePrincipleTokenManager(SQLServerDataSource ds, String tenetId, String clientId, String secret) {
        this.ds = ds;
        this.secret = secret;
        this.clientId = clientId;
        this.tenetId = tenetId;
    }
 
    public boolean getConfirmTokenFlag(){
        return this.confirmTokenFlag;
    }
 
    private void setAccessToken(String token){
        this.ds.setAccessToken(token);
    }
 
 
 
 
    @Override
    public void run() {
        logger.info("Fetching Service Principle accessToken");
        String result = "";
        HttpPost post = new HttpPost(ENDPOINT+this.tenetId+"/oauth2/token");
        List<NameValuePair> urlParameters = new ArrayList<>();
        urlParameters.add(new BasicNameValuePair("grant_type", GRANT_TYPE));
        urlParameters.add(new BasicNameValuePair("client_id", this.clientId));
        urlParameters.add(new BasicNameValuePair("client_secret", this.secret));
        urlParameters.add(new BasicNameValuePair("resource", RESOURCE));
 
        try{
 
            post.setEntity(new UrlEncodedFormEntity(urlParameters));
            CloseableHttpClient httpClient = HttpClients.createDefault();
            CloseableHttpResponse response = httpClient.execute(post);
            result = EntityUtils.toString(response.getEntity());
            ObjectNode node = new ObjectMapper().readValue(result, ObjectNode.class);
 
            if (node.has("access_token")) {
                result = node.get("access_token").toString();
            }
 
        }catch (Exception ex){
            logger.error(ex.getMessage(),ex);
        }
 
        this.setAccessToken(result.substring(1, result.length()-1));
        confirmTokenFlag=true;
        logger.info("set confirmTokenFlag true");
 
 
    }
}

呼叫者会是这样

        SQLServerDataSource ds = new SQLServerDataSource();

        AzureServicePrincipleTokenManager azureServicePrincipleTokenManager = new AzureServicePrincipleTokenManager(ds,"your tenentID","your clientID","your secret");
        ScheduledExecutorService sches = Executors.newScheduledThreadPool(1);
        sches.scheduleWithFixedDelay(azureServicePrincipleTokenManager, 0, 45, TimeUnit.MINUTES);
        logger.info("----ExecuterService started the Runnable task");

        while (azureServicePrincipleTokenManager.getConfirmTokenFlag()!=true){

            ds.getAccessToken(); //I wonder If i leave while body balnk it never become true. so intentionally i'm calling ds.getAccessToken();
        }
            logger.info("----get the token after settingup  "+ds.getAccessToken());

调用方线程如何等待ScheduledExecutorService下的任务完成任务

3 个答案:

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