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Singleton Java类返回空值


春风助手
2025-03-21 01:38:17 (18小时前)

我创建了一个Java类，该类返回一个数据库连接对象。但是它在调用者方法处返回空值。当我在调试模式下运行代码时，它不会转到方法本身。需要建议。

  1. package com.cisco.installbase.hiveconnector;
  3. import java.sql.DriverManager;
  4. import java.sql.SQLException;
  5. import java.sql.Connection;
  7. public class CreateConnection {
  9.     private static Connection instance = null;
  10.     static final String drivername = "org.apache.hive.jdbc.HiveDriver";
  12.     private CreateConnection() {
  14.         try {
  15.             Class.forName(drivername);
  16.             // instance =
  17.             // DriverManager.getConnection("jdbc:hive2://hddev-c01-edge-01:20000/",
  18.             // "phodisvc", "B1GD4T4dev");
  19.             // for hive 1 use this ------> instance =
  20.             // DriverManager.getConnection("thrift://hddev-c01-edge-02:9083");
  21.             instance = DriverManager.getConnection("thrift://hddev-c01-edge-02:9083");
  22.             System.out.println("get instance"+instance);
  23.             Constants.setFlag(true);
  24.         } catch (ClassNotFoundException e) {
  25.             e.printStackTrace();
  26.             Constants.setFlag(false);
  27.         } catch (SQLException e) {
  28.             e.printStackTrace();
  29.             Constants.setFlag(false);
  30.         }
  31.     }
  33.     public static Connection getInstance() {
  34.         Constants.setFlag(true);
  35.         return instance;
  36.     }
  37. }

下面是调用getInstance（）方法的代码

  1. package com.cisco.installbase.hiveconnector;
  3. import java.util.Date;
  5. public class MainApp {
  7.     private static final String hiveDB = ReadProperties.getInstance().getProperty("hive_db");
  8.     private static final String logTable = ReadProperties.getInstance().getProperty("IB_log_table");
  9.     private static final String dataGovernanceLogTable = ReadProperties.getInstance().getProperty("SR_DG_table");
  10.     private static final String dataGovernanceMasterTable = ReadProperties.getInstance()
  11.             .getProperty("SR_DG_master_table");
  13.     private static final String count_xxccs_ds_sahdr_core = "select count(*) from " + hiveDB + "."
  14.             + "xxccs_ds_sahdr_core";
  15.     private static final String count_mtl_system_items_b = "select count(*) from " + hiveDB + "."
  16.             + "mtl_system_items_b";
  17.     private static final String count_xxccs_scdc_product_profile = "select count(*) from " + hiveDB + "."
  18.             + "xxccs_scdc_product_profile";
  19.     private static final String count_xxccs_ds_cvdprdline_detail = "select count(*) from " + hiveDB + "."
  20.             + "xxccs_ds_cvdprdline_detail";
  21.     private static final String count_xxccs_ds_instance_detail = "select count(*) from " + hiveDB + "."
  22.             + "xxccs_ds_instance_detail";
  24.     private static int currentJobID = 0;
  25.     private static Date startTime = null;
  26.     private static Date stopTime = null;
  27.     private static int runTime = 0;
  29.     static CommonDBUtilities commonDB = new CommonDBUtilities();
  30.     static ShellUtilities shellUtilities = new ShellUtilities();
  31.     static SqoopUtility sqoop = new SqoopUtility();
  33.     public static void main(String[] args) {
  35.         MainApp.startTimeLogger();
  36.         System.out.println("Started the Job");
  38.     }
  40.     public static void startTimeLogger() {
  41.         // getting the Job ID and the start time for the log table
  43.         if (Constants.isFlag()) {
  44.             currentJobID = commonDB.getMaximumJobID();
  45.             startTime = commonDB.getTime();
  46.             MainApp.importTables();
  47.             System.out.println("executing startTimeLogger");
  48.         } else {
  49.             MainApp.onFailure();
  50.             JobMailer.PostMail("IB Load Failed", "Load failed while logging method name startTimeLogger()");
  51.             System.out.println("executing startTimeLogger failed");
  52.         }
  53.     }
  55.     public static void importTables() {
  56.         // Delete target directory before running the sqoop imports
  58.         if (Constants.isFlag()) {
  59.             shellUtilities.DeleteDirectory(Constants.getMtlSystems());
  60.             shellUtilities.DeleteDirectory(Constants.getProductLine());
  61.             shellUtilities.DeleteDirectory(Constants.getInstanceDetail());
  62.             shellUtilities.DeleteDirectory(Constants.getProductLine());
  63.             shellUtilities.DeleteDirectory(Constants.getHeaderCore());
  65.             // Run the sqoop imports to load the data from oracle to hive
  67.             sqoop.runSqoop();
  68.             MainApp.getCounts();
  69.             System.out.println("executing importTables");
  70.         } else {
  71.             MainApp.onFailure();
  72.             JobMailer.PostMail("IB Load Failed", "Load failed while running sqoop import method name importTables()");
  73.             System.out.println("executing importTables failed");
  74.         }
  76.     }
  78.     public static void getCounts() {
  80.         // Get the record counts for all the IB tables pulled
  82.         if (Constants.isFlag()) {
  83.             commonDB.getCounts(count_xxccs_ds_instance_detail);
  84.             commonDB.getCounts(count_xxccs_ds_cvdprdline_detail);
  85.             commonDB.getCounts(count_xxccs_scdc_product_profile);
  86.             commonDB.getCounts(count_mtl_system_items_b);
  87.             commonDB.getCounts(count_xxccs_ds_sahdr_core);
  88.             MainApp.stopTimeLogger();
  89.             System.out.println("executing getCounts");
  90.         } else {
  91.             MainApp.onFailure();
  92.             JobMailer.PostMail("IB Load Failed", "Load failed while getting counts method name getCounts()");
  93.             System.out.println("executing getCounts failed");
  94.         }
  95.     }
  97.     public static void stopTimeLogger() {
  98.         // Get the stop time or end time
  99.         if (Constants.isFlag()) {
  100.             stopTime = commonDB.getTime();
  101.             MainApp.runTimeLogger();
  102.             System.out.println("executing stopTimeLogger");
  103.         } else {
  104.             MainApp.onFailure();
  105.             JobMailer.PostMail("IB Load Failed", "Load failed while end logging method name stopTimeLogger()");
  106.             System.out.println("executing stopTimeLogger failed");
  107.         }
  108.     }
  110.     public static void runTimeLogger() {
  111.         // Get the run time or total time taken
  112.         if (Constants.isFlag()) {
  113.             runTime = (int) (stopTime.getTime() - startTime.getTime()) / 1000 * 60 * 60 * 24;
  114.             MainApp.onSuccess();
  115.             MainApp.logGovernance();
  116.             System.out.println("executing runTimeLogger");
  117.         } else {
  118.             MainApp.onFailure();
  119.             JobMailer.PostMail("IB Load Failed", "Load failed while runtime logging method name runTimeLogger()");
  120.             System.out.println("executing runTimeLogger failed");
  121.         }
  122.     }
  124.     public static void logGovernance() {
  125.         // IB Data governance
  127.         if (Constants.isFlag()) {
  128.             String dataGovernance = "Insert into table " + hiveDB + "." + dataGovernanceLogTable
  129.                     + " select Data_Asset_Reference,File_Name,Origin_System,Transfer_System," + startTime
  130.                     + ",Column_Reference,Element_Reference,Rule_Priority,Delete_By_Date,Classification,Geographic_Inclusion,Geographic_Restriction,Group_Inclusion,Group_Restriction,Reserved from "
  131.                     + hiveDB + "." + dataGovernanceMasterTable;
  132.             commonDB.InsertToTable(dataGovernance);
  133.             System.out.println("executing logGovernance");
  134.         } else {
  135.             MainApp.onFailure();
  136.             JobMailer.PostMail("IB Load Failed",
  137.                     "Load failed while inserting into datagovernance method name logGovernance()");
  138.             System.out.println("executing logGovernance failed");
  139.         }
  140.     }
  142.     public static void onFailure() {
  143.         // Write to log on Failure
  144.         String insertOnFailure = "insert into table " + hiveDB + "." + logTable + " select " + currentJobID + ","
  145.                 + stopTime + "," + runTime + "," + "FAILED from " + hiveDB + "." + "dual" + " limit 1; ";
  146.         commonDB.InsertToTable(insertOnFailure);
  147.         JobMailer.PostMail("IB Load Failed", "Load failed");
  148.         System.out.println("executing onFailure");
  149.     }
  151.     public static void onSuccess() {
  152.         // Write to log on Success
  153.         String insertOnSuccess = "insert into table " + hiveDB + "." + logTable + " select " + currentJobID + ","
  154.                 + stopTime + "," + runTime + "," + "SUCCESS from " + hiveDB + "." + "dual" + " limit 1; ";
  155.         commonDB.InsertToTable(insertOnSuccess);
  156.         JobMailer.PostMail("IB Load Successfully completed", "Load completed");
  157.         System.out.println("executing onSuccess");
  158.     }
  160. }
2 条回复
  1. 1# 只怕再见是故人 | 2020-08-18 12-01

    您对sigleton的实现是错误的。您永远不会调用构造函数。这是实现单例的正确方法。

    1. public static Connection getInstance() {
    2.         if (instance==null){
    3.             instance = new CreateConnection();
    4.         }
    5.         Constants.setFlag(true);
    6.         return instance;
    7.     }
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