我正在尝试将一个应用程序构建为学习体验。我收到一个空指针异常，但是这是第二次调用代码时发生的情况。
因此，我的代码将其称为启动过程的一部分。
// Sanity checks
sanity = new SanityChecks();
logger.info("Checking sanity...");
try {
sanity.doBasicChecks();
logger.info("It all looks sane.");
}
catch( final Exception ex){
logger.error("Something is wrong, we are not sane. Aborting...", ex);
stop();
}
其他类是：
package nz.co.great_ape.tempusFugit;
import com.almworks.sqlite4java.SQLite;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
/**
* Checks to see if all is ok for standard usage of tempusFugit.
*
* Checks for valid paths, existing database etc, if not assumes that
* this is the first time tempusFugit has been run for this user and
* tries to set up the basic files and data.
*
* @author Rob Brown-Bayliss
* Created on 2/11/14
*/
public class SanityChecks {
public static final Logger logger = LoggerFactory.getLogger(AppConsts.LOGGER_NAME);
public SanityChecks() {
// todo
// todo
SQLite.setLibraryPath(AppConsts.HOME_DIR); // TODO: Why is this required? can we not place the native libs somewhere else or in the jar?
// todo
// todo
}
/**
* Performs basic checks to see if it is ok to run the app. If not it will attempt to
* set up for first time use.
*
* @return true if all is ok
*/
public boolean doBasicChecks() {
logger.info("Starting basic checks...");
if (!HomeDirExists()) {
return false;
}
if (!DatabaseExists()) {
logger.info("Trying to create a new database.");
DatabaseUpgrade dug = new DatabaseUpgrade();
if (!dug.upGrade()) {
return false;
}
logger.info("Created a new database.");
// At this point a usable database should exist and it should be current
}
if (!DatabaseVersionCorrect()) {
// // If the database is old we will upgrade it to the current version.
// DatabaseUpgrade dug = new DatabaseUpgrade();
// if (!dug.upGrade()) {
// return false;
// }
logger.info("is this it?.");
}
// At this point all basic checks have passed and we are good to go...
logger.info("Basic checks are complete. All is good in the universe...");
return true;
}
/**
* Checks if the app home directory exists, if not it tries to create it.
*
* @return true if exists or was able to create the directory
*/
private boolean HomeDirExists() {
if (!Files.isDirectory(Paths.get(AppConsts.HOME_DIR))) {
try {
Files.createDirectory(Paths.get(AppConsts.HOME_DIR));
}
catch (IOException io) {
logger.error("The directory " + AppConsts.HOME_DIR + " does not exist and could not be created. This is not the best but we can survive.", io);
return false;
}
}
logger.info("The directory " + AppConsts.HOME_DIR + " exists. This is good.");
return true;
}
/**
* Checks if the SQLite database exists, if not it tries to create it.
* or was able to create the database
*
* @return true if the database exists
*/
private boolean DatabaseExists() {
if (Files.notExists(Paths.get(AppConsts.TF_DATABASE))) {
logger.error("The database " + AppConsts.TF_DATABASE + " does not exist. This is bad.");
return false;
}
logger.info("The database " + AppConsts.TF_DATABASE + " exists. This is good.");
return true;
}
/**
* Checks if the SQLite database is correct for this version.
*
* @return true if correct version
*/
private boolean DatabaseVersionCorrect() {
Integer expectedVersion = AppConsts.TF_DATABASE_VERSION;
logger.info("Checking the database version is correct. Looking for version "+ expectedVersion + "." );
DatabaseUpgrade dug = new DatabaseUpgrade();
logger.info("Checking the database version is correct. Looking for version "+ expectedVersion + "." );
Integer currentVersion = dug.getVersion();
if (currentVersion < expectedVersion) {
logger.info("Expected version " + expectedVersion + ", but database is version " + currentVersion + ". This is bad.");
return false;
}
logger.info("The database version is correct. This is good.");
return true;
}
}
和：
package nz.co.great_ape.tempusFugit;
import com.almworks.sqlite4java.*;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.io.File;
import java.nio.file.Files;
import java.nio.file.Paths;
/**
* Setup the database for current version tempusFugit. This will upgrade an
* existing database or create a new empty database if required.
*
* @author Rob Brown-Bayliss
* Created on 4/11/14
*/
public class
DatabaseUpgrade {
public static final Logger logger = LoggerFactory.getLogger(AppConsts.LOGGER_NAME);
private SQLiteConnection dbConn = null;
private SQLiteQueue sQueue = null;
private int currentVersion;
public DatabaseUpgrade() {
}
/**
* Attempts to upgrade the existing database to the current version, or if
* there is no existing database then create one suitable for the current app version.
*
* @return true if there is a current and usable database
*/
public boolean upGrade() {
logger.info(" Started an upgrade on the database, if the database does not exist it will be created at the current version, ");
logger.info(" if it exists but is an older version it will be upgraded to the current version.");
if (openDatabase()) {
currentVersion = getVersion();
if (currentVersion == AppConsts.FAIL) {
logger.info("Database version is unknown. The file will be deleted and a new database created. We can survive this.");
// TODO: Ask user if we should delete the old one or make a backup?
closeDatabase();
deleteDatabase();
openDatabase();
}
if (currentVersion != AppConsts.TF_DATABASE_VERSION) {
logger.info("Current Database version is " + currentVersion);
// TODO: Backup current database.
if (currentVersion < 1) {
if (!makeVersionOne()) {
logger.error("Unable to upgrade the database. This is VERY bad.");
return false;
}
}
currentVersion = 1;
}
closeDatabase(); // good practice
}
logger.info("The database is the current version. This is good.");
return true;
}
/**
* Turns a blank SQLite database into a tempusFugit version 1 database by
* adding the required tables and data.
*/
private boolean makeVersionOne() {
logger.info("Attempting to upgrade to version 1.");
String CT_SQL = "CREATE TABLE IF NOT EXISTS dbVersion (id INTEGER PRIMARY KEY AUTOINCREMENT, version INTEGER NOT NULL UNIQUE, ";
CT_SQL = CT_SQL + "upgraded INTEGER(4) NOT NULL DEFAULT (strftime('%s','now'))); ";
String IN_SQL = "INSERT INTO dbVersion(version) values (1); ";
try {
execSQL("BEGIN TRANSACTION; ");
execSQL(CT_SQL); // create the table
execSQL(IN_SQL); // insert the record
execSQL("COMMIT; ");
}
catch (Exception ex) {
logger.error("Attempted upgrade of " + AppConsts.TF_DATABASE + " to version 1 has failed. This is VERY bad.", ex);
return false;
}
logger.info("The database has been upgraded to version 1. This is good.");
return true;
}
private Integer execSQL(String SQL) {
return sQueue.execute(new SQLiteJob<Integer>() {
protected Integer job(SQLiteConnection con) throws SQLiteException {
SQLiteStatement st = null;
try {
st = con.prepare(SQL);
st.step();
return AppConsts.SUCCESS;
}
catch (Exception ex) {
logger.error("Tried to execute SQL: " + SQL, ex);
return AppConsts.FAIL;
}
finally {
if (st != null) {
st.dispose();
}
}
}
}).complete();
}
/**
* Gets the current database version
*
* @return version as an int
*/
public int getVersion() {
return sQueue.execute(new SQLiteJob<Integer>() {
protected Integer job(SQLiteConnection con) throws SQLiteException {
SQLiteStatement st = null;
try {
st = con.prepare("SELECT version, upgraded FROM dbVersion ORDER BY upgraded DESC LIMIT 1;");
st.step();
return st.columnInt(0);
}
catch (Exception ex) {
logger.error("The database version of " + AppConsts.TF_DATABASE + " is unknown. This is bad.", ex);
return AppConsts.FAIL;
}
finally {
if (st != null) {
st.dispose();
}
}
}
}).complete();
}
/**
* Opens an existing SQLite database or creates a new blank database
* if none exists.
*
* @return false if there is a problem. // TODO: Is it possible to have a problem?
*/
private boolean openDatabase() {
try {
dbConn = new SQLiteConnection(new File(AppConsts.TF_DATABASE));
dbConn.open(true);
sQueue = new SQLiteQueue(new File(AppConsts.TF_DATABASE));
sQueue.start();
return true;
}
catch (Exception ex) {
logger.error("The database " + AppConsts.TF_DATABASE + " could not be opened or created. This is VERY bad.", ex);
return false;
}
}
/**
* Closes an open database.
*
* @return false if there is a problem. // TODO: Is it possible to have a problem?
*/
private boolean closeDatabase() {
try {
if (dbConn != null) {
dbConn.dispose();
}
return true;
}
catch (Exception ex) {
logger.error("The database " + AppConsts.TF_DATABASE + " could not be closed.", ex);
return false;
}
}
/**
* Deletes an existing database.
*
* @return false if there is a problem. // TODO: Is it possible to have a problem?
*/
private boolean deleteDatabase() {
try {
Files.delete(Paths.get(AppConsts.TF_DATABASE));
logger.info("The database " + AppConsts.TF_DATABASE + " has been deleted.");
return true;
}
catch (Exception ex) {
logger.error("The database " + AppConsts.TF_DATABASE + " could not be deleted.", ex);
return false;
}
}
}
Plus the constants:
package nz.co.great_ape.tempusFugit;
/**
* Constants used by tempusFugit
*
* @author Rob Brown-Bayliss
* Created on 31/10/14
*/
public class AppConsts {
// Application
public static final String APP_NAME = "Tempus Fugit";
public static final String VERSION_NUMBER = "0.0.1";
// Debug Mode On-Off
public static final boolean DEBUG_MODE = true;
// Data files and paths
public static final String FS = System.getProperty("file.separator");
public static final String HOME_DIR = System.getProperty("user.home") + FS + ".tempusFugit"; // This is the tempusFugit home, not the users home.
public static final String USER_NAME = System.getProperty("user.name");
public static final String LOGGER_NAME = "nz.co.great_ape.tempusFugit";
public static final String LOG_FILE = HOME_DIR + FS + "tempusFugit.log";
// Database
public static final String TF_DATABASE = HOME_DIR + FS + "tfData.sql";
public static final int TF_DATABASE_VERSION = 1; // This is the current version of the database
// Error codes
public static final int UNKNOWN = -1;
public static final int FAIL = 0;
public static final int SUCCESS = 1;
}
我不知道的是为什么调用if（！DatabaseVersionCorrect（））会因空指针而崩溃。
有人可以帮忙吗？
这是堆栈跟踪
/usr/lib/jvm/java-8-oracle/bin/java -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:49764,suspend=y,server=n -javaagent:/home/rob/Projects/IntelliJ/plugins/Groovy/lib/agent/gragent.jar -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-8-oracle/jre/lib/jsse.jar:/usr/lib/jvm/java-8-oracle/jre/lib/management-agent.jar:/usr/lib/jvm/java-8-oracle/jre/lib/deploy.jar:/usr/lib/jvm/java-8-oracle/jre/lib/javaws.jar:/usr/lib/jvm/java-8-oracle/jre/lib/plugin.jar:/usr/lib/jvm/java-8-oracle/jre/lib/resources.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jfr.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jfxswt.jar:/usr/lib/jvm/java-8-oracle/jre/lib/rt.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jce.jar:/usr/lib/jvm/java-8-oracle/jre/lib/charsets.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/jfxrt.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/cldrdata.jar:/home/rob/Projects/tempusFugit/build/classes/main:/home/rob/Projects/tempusFugit/build/resources/main:/home/rob/.gradle/caches/modules-2/files-2.1/org.slf4j/slf4j-api/1.7.7/2b8019b6249bb05d81d3a3094e468753e2b21311/slf4j-api-1.7.7.jar:/home/rob/.gradle/caches/modules-2/files-2.1/com.almworks.sqlite4java/sqlite4java/1.0.392/d6234e08ff4e1607ff5321da2579571f05ff778d/sqlite4java-1.0.392.jar:/home/rob/.gradle/caches/modules-2/files-2.1/ch.qos.logback/logback-classic/1.1.2/b316e9737eea25e9ddd6d88eaeee76878045c6b2/logback-classic-1.1.2.jar:/home/rob/.gradle/caches/modules-2/files-2.1/ch.qos.logback/logback-core/1.1.2/2d23694879c2c12f125dac5076bdfd5d771cc4cb/logback-core-1.1.2.jar:/home/rob/Projects/IntelliJ/lib/idea_rt.jar nz.co.great_ape.tempusFugit.MainApp
已连接到目标VM，地址：“ 127.0.0.1:49764”，传输：“ socket”
10：43：43.371 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-时间过得真快...
10：43：43.379 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-https://www.youtube.com/watch?v=ESto79osxOY
10：43：43.379 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-Tempus Fugit版本：0.0.1
10：43：43.379 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-javafx.runtime.version：8.0.25-b17
10：43：43.380 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-登录为：rob
10：43：43.383 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-检查健全性...
10：43：43.383 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-开始基本检查...
10：43：43.393 [JavaFX应用程序线程]信息nz.co.great_ape.tempusFugit-目录/home/rob/.tempusFugit存在。很好
10：43：43.394 [JavaFX应用程序线程]错误nz.co.great_ape.tempusFugit-数据库/home/rob/.tempusFugit/tfData.sql不存在。这是不好的。
10：43：43.394 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-尝试创建新数据库。
10：43：43.397 [JavaFX应用程序线程]信息nz.co.great_ape.tempusFugit-开始对数据库进行升级，如果该数据库不存在，它将以当前版本创建，
10：43：43.397 [JavaFX应用程序线程]信息nz.co.great_ape.tempusFugit-如果存在，但它是较旧的版本，它将升级到当前版本。
2014年11月30日10:43:43 com.almworks.sqlite4java.Internal log
INFO：[sqlite] DB [1]：实例化[/home/rob/.tempusFugit/tfData.sql]
2014年11月30日10:43:43 com.almworks.sqlite4java.Internal log
信息：[sqlite]内部：从/home/rob/.tempusFugit/libsqlite4java-linux-amd64-1.0.392.so加载sqlite4java-linux-amd64-1.0.392
2014年11月30日10:43:43 com.almworks.sqlite4java.Internal log
INFO：[sqlite]内部：已加载sqlite 3.8.7，包装器1.3
2014年11月30日10:43:43 com.almworks.sqlite4java.Internal log
信息：[sqlite] DB [1]：已打开
2014年11月30日10:43:43 com.almworks.sqlite4java.Internal log
INFO：[sqlite] DB [2]：实例化[/home/rob/.tempusFugit/tfData.sql]
2014年11月30日10:43:43 com.almworks.sqlite4java.Internal log
信息：[sqlite] DB [2]：已打开
2014年11月30日10:43:43 com.almworks.sqlite4java.Internal log
信息：[sqlite] DB [1]：连接已关闭
2014年11月30日10:43:43 com.almworks.sqlite4java.Internal log
INFO：[sqlite] DB [3]：实例化[/home/rob/.tempusFugit/tfData.sql]
2014年11月30日10:43:43 com.almworks.sqlite4java.Internal log
信息：[sqlite] DB [3]：已打开
10：43：43.507 [SQLiteQueue [tfData.sql]]错误nz.co.great_ape.tempusFugit-/home/rob/.tempusFugit/tfData.sql的数据库版本未知。这是不好的。
com.almworks.sqlite4java.SQLiteException：[1] DB [2] prepare（）SELECT版本，是从dbVersion升级的，而升级是DESC LIMIT 1的； [没有这样的表：dbVersion]
在com.almworks.sqlite4java.SQLiteConnection.throwResult（SQLiteConnection.java:1436）〜[sqlite4java-1.0.392.jar：392]
在com.almworks.sqlite4java.SQLiteConnection.prepare（SQLiteConnection.java:580）〜[sqlite4java-1.0.392.jar：392]
在com.almworks.sqlite4java.SQLiteConnection.prepare（SQLiteConnection.java:635）〜[sqlite4java-1.0.392.jar：392]
在com.almworks.sqlite4java.SQLiteConnection.prepare（SQLiteConnection.java:622）〜[sqlite4java-1.0.392.jar：392]
在nz.co.great_ape.tempusFugit.DatabaseUpgrade $ 2.job（DatabaseUpgrade.java:121）[main /：na]
在nz.co.great_ape.tempusFugit.DatabaseUpgrade $ 2.job（DatabaseUpgrade.java:117）[main /：na]
在com.almworks.sqlite4java.SQLiteJob.execute（SQLiteJob.java:372）上[sqlite4java-1.0.392.jar：392]
在com.almworks.sqlite4java.SQLiteQueue.executeJob（SQLiteQueue.java:534）上[sqlite4java-1.0.392.jar：392]
在com.almworks.sqlite4java.SQLiteQueue.queueFunction（SQLiteQueue.java:667）上[sqlite4java-1.0.392.jar：392]
在com.almworks.sqlite4java.SQLiteQueue.runQueue（SQLiteQueue.java:623）[sqlite4java-1.0.392.jar：392]
在com.almworks.sqlite4java.SQLiteQueue.access $ 000（SQLiteQueue.java:77）[sqlite4java-1.0.392.jar：392]
在com.almworks.sqlite4java.SQLiteQueue $ 1.run（SQLiteQueue.java:205）[sqlite4java-1.0.392.jar：392]
在java.lang.Thread.run（Thread.java:745）[na：1.8.0_25]
10：43：43.508 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-数据库版本未知。该文件将被删除，并创建一个新的数据库。我们可以生存下来。
10：43：43.509 [JavaFX应用程序线程]信息nz.co.great_ape.tempusFugit-数据库/home/rob/.tempusFugit/tfData.sql已删除。
10：43：43.510 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-当前数据库版本为0
10：43：43.510 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-尝试升级到版本1。
2014年11月30日10:43:43 com.almworks.sqlite4java.Internal log
INFO：[sqlite] DB [4]：实例化[/home/rob/.tempusFugit/tfData.sql]
2014年11月30日10:43:43 com.almworks.sqlite4java.Internal log
信息：[sqlite] DB [4]：已打开
2014年11月30日10:43:43 com.almworks.sqlite4java.Internal log
信息：[sqlite] DB [3]：连接已关闭
10：43：43.640 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-数据库已升级到版本1。这很好。
10：43：43.640 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-数据库是当前版本。很好
10：43：43.640 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-创建了一个新数据库。
10：43：43.640 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-检查数据库版本是否正确。寻找版本1。
10：43：43.640 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-检查数据库版本是否正确。寻找版本1。
10：43：43.641 [JavaFX应用程序线程]错误nz.co.great_ape.tempusFugit-出问题了，我们并不理智。正在中止...
java.lang.NullPointerException：空
在nz.co.great_ape.tempusFugit.DatabaseUpgrade.getVersion（DatabaseUpgrade.java:117）〜[main /：na]
在nz.co.great_ape.tempusFugit.SanityChecks.DatabaseVersionCorrect（SanityChecks.java:111）〜[main /：na]
在nz.co.great_ape.tempusFugit.SanityChecks.doBasicChecks（SanityChecks.java:54）〜[main /：na]
在nz.co.great_ape.tempusFugit.MainApp.start（MainApp.java:78）〜[main /：na]
在com.sun.javafx.application.LauncherImpl.lambda $ launchApplication1 $ 153（LauncherImpl.java:821）[jfxrt.jar：na]
在com.sun.javafx.application.LauncherImpl $$ Lambda $ 56 / 1015064561.run（未知来源）[jfxrt.jar：na]
在com.sun.javafx.application.PlatformImpl.lambda $ runAndWait $ 166（PlatformImpl.java:323）[jfxrt.jar：na]
在com.sun.javafx.application.PlatformImpl $$ Lambda $ 50 / 591723622.run（未知来源）[jfxrt.jar：na]
在com.sun.javafx.application.PlatformImpl.lambda $ null $ 164（PlatformImpl.java:292）[jfxrt.jar：na]
在com.sun.javafx.application.PlatformImpl $$ Lambda $ 52 / 1657335803.run（未知来源）[jfxrt.jar：na]
在java.security.AccessController.doPrivileged（本机方法）[na：1.8.0_25]
在com.sun.javafx.application.PlatformImpl.lambda $ runLater $ 165（PlatformImpl.java:291）[jfxrt.jar：na]
在com.sun.javafx.application.PlatformImpl $$ Lambda $ 51 / 1166726978.run（未知来源）[jfxrt.jar：na]
在com.sun.glass.ui.InvokeLaterDispatcher $ Future.run（InvokeLaterDispatcher.java:95）[jfxrt.jar：na]
在com.sun.glass.ui.gtk.GtkApplication._runLoop（本机方法）[jfxrt.jar：na]
在com.sun.glass.ui.gtk.GtkApplication.lambda $ null $ 45（GtkApplication.java:126）[jfxrt.jar：na]
在com.sun.glass.ui.gtk.GtkApplication $$ Lambda $ 42 / 1167116739.run（未知来源）[jfxrt.jar：na]
在java.lang.Thread.run（Thread.java:745）[na：1.8.0_25]
10：43：43.641 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-游戏结束...
10：43：44.563 [JavaFX应用程序线程] INFO nz.co.great_ape.tempusFugit-游戏结束...
最佳答案
问题是你打电话给你
DatabaseUpgrade dug = new DatabaseUpgrade();
logger.info(...);
Integer currentVersion = dug.getVersion();
但是您在
dbConn中的sQueue和DatabaseUpgrade仍然为空。由于您没有调用私有的openDatabase()方法来初始化变量。因此，当您调用getVersion()时，您的sQueue.execute(...)爆炸了，因为您无法在空对象上调用方法。
关于java - SQLite Java和sqlite4java，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/27199470/