标签: classnotfoundexception

我正在从android网站学习教程.

但是当我运行应用程序时,它会提示Unable to instantiate activity component有关classNotFoundException的信息.但是在manifestxt.xml文件中注册了MainActivity.我不知道问题出在哪里.这是完整的错误日志.

05-03 18:59:00.425: E/AndroidRuntime(20858): FATAL EXCEPTION: main
05-03 18:59:00.425: E/AndroidRuntime(20858): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.android.effectivenavigation/com.example.android.effectivenavigation.MainActivity}: java.lang.ClassNotFoundException: com.example.android.effectivenavigation.MainActivity
05-03 18:59:00.425: E/AndroidRuntime(20858):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
05-03 18:59:00.425: E/AndroidRuntime(20858):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
05-03 18:59:00.425: E/AndroidRuntime(20858):    at android.app.ActivityThread.access$600(ActivityThread.java:130)
05-03 18:59:00.425: E/AndroidRuntime(20858):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
05-03 18:59:00.425: E/AndroidRuntime(20858):    at android.os.Handler.dispatchMessage(Handler.java:99)
05-03 18:59:00.425: E/AndroidRuntime(20858):    at android.os.Looper.loop(Looper.java:137)
05-03 18:59:00.425: E/AndroidRuntime(20858):    at android.app.ActivityThread.main(ActivityThread.java:4745)
05-03 18:59:00.425: E/AndroidRuntime(20858):    at java.lang.reflect.Method.invokeNative(Native Method)
05-03 18:59:00.425: E/AndroidRuntime(20858):    at java.lang.reflect.Method.invoke(Method.java:511)
05-03 18:59:00.425: E/AndroidRuntime(20858):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
05-03 18:59:00.425: …

Java真的是新手，还是讲西班牙语的人，所以，请尽我所能帮助您理解我:)。我制作了一个程序，该程序管理用于存储客户端，有关客户端的信息等的mysql数据库。并生成（或尝试...）报告。我从Eclipse Market（BTW，使用Eclipse Kepler）安装了JasperReports。在学习了一些教程之后，我开始按参数创建报告。它只是识别一个客户端的一个参数。那不是问题。当我单击我的按钮以生成报告时出现问题，该报告包含以下代码：

JButton btnOk = new JButton("OK");
    btnOk.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent arg0) {
            String doc = jftxtDni.getText();
            String sql;
            boolean respuesta = false;
            ConexionBaseDatos cc = new ConexionBaseDatos();

            sql = "SELECT * FROM clientes WHERE DNI = '"+doc+"'";

            rs = cc.Consultar(sql);

                try 
                {
                    while (rs.next())
                    {
                    respuesta = true;
                    }
                }
                catch (SQLException e) 
                {
                    JOptionPane.showMessageDialog(null, "error sql: "+e.getMessage());
                }    

                if (respuesta)
                {
                    ConexionBaseDatos cd = new ConexionBaseDatos();
                    Connection cn = cd.Conectar();
                    JasperReport jr = null;
                    String …

我很确定这是因为版本不匹配，所以我共享我的所有 pom 文件，当我在必须使用 cognito 的模块之一中工作时，我有项目模块，我添加了依赖项并将所有其他更改为新版本因为 cognito 不支持旧版本，但现在在另一个模块中，我收到此错误

     <dependencies>
              <dependency>
                <groupId>com.amazonaws</groupId>
                <artifactId>aws-java-sdk-bom</artifactId>
                <version>1.11.109</version>
                <type>pom</type>
                <scope>import</scope>
              </dependency>
    </dependencies>

     </dependencyManagement>

            <dependencies>


                <dependency>
                    <groupId>javax.servlet</groupId>
                    <artifactId>javax.servlet-api</artifactId>
                    <version>3.1.0</version>
                </dependency>

                <dependency>
                    <groupId>org.postgresql</groupId>
                    <artifactId>postgresql</artifactId>
                    <version>9.4-1201-jdbc41</version>
                </dependency>

                <dependency>
                    <groupId>net.postgis</groupId>
                    <artifactId>postgis-jdbc</artifactId>
                    <version>2.2.0</version>
                    <exclusions>
                        <exclusion>
                            <groupId>postgresql</groupId>
                            <artifactId>postgresql</artifactId>
                        </exclusion>
                    </exclusions>
                </dependency>

                <!-- Jackson -->
                <dependency>
                    <groupId>com.fasterxml.jackson.core</groupId>
                    <artifactId>jackson-core</artifactId>
                    <version>2.6.6</version>
                </dependency>
                <dependency>
                    <groupId>com.fasterxml.jackson.core</groupId>
                    <artifactId>jackson-databind</artifactId>
                    <version>2.6.6</version>
                </dependency>


                <!-- Spring -->
                <dependency>
                    <groupId>org.springframework</groupId>
                    <artifactId>spring-web</artifactId>
                    <version>${org.springframework.version}</version>
                </dependency>
                <dependency>
                    <groupId>org.springframework</groupId>
                    <artifactId>spring-context</artifactId>
                    <version>${org.springframework.version}</version>
                </dependency>
                <dependency>
                    <groupId>org.springframework</groupId>
                    <artifactId>spring-aspects</artifactId>
                    <version>${org.springframework.version}</version>
                </dependency>
                <dependency>
                    <groupId>org.springframework</groupId>
                    <artifactId>spring-webmvc</artifactId>
                    <version>${org.springframework.version}</version>
                </dependency>
                <dependency>
                    <groupId>org.springframework</groupId>
                    <artifactId>spring-tx</artifactId>
                    <version>${org.springframework.version}</version>
                </dependency> …

在 Eclipse 中运行此代码时出现错误。我已经创建了Student.java文件：

public class Student {
    private int id;
    private String name;
    private String email;
    private int marks;
    
    // getters/setters
}

我已经创建了Student.hbm.xml文件：

<!DOCTYPE hibernate-mapping PUBLIC 
     "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
     "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
          
    <hibernate-mapping>
    <class name="bean.Student" table="student">
            <id name="id" column="sid"></id>
            <property name="name"  column="sname"></property>
            <property name="email" column="semail"></property>
            <property name="marks" column="smarks"></property>
    </class>
    </hibernate-mapping>

我已经创建了hibernate.cfg.xml文件：

 <!DOCTYPE hibernate-configuration PUBLIC
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
        
    <hibernate-configuration>
    <session-factory>
        <property name="connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
        <property name="connection.url">jdbc:oracle:thin:@localhost:1521:wind</property>
        <property name="connection.username">localuser</property>
        <property name="connection.password">localuser</property>
        <property name="connection.poolsize">5</property>
            
        <property name="dialect">org.hibernate.dialect.OracleDialect</property>
            
        <mapping resource="resources/student.hbm.xml"/> …

我有一个部署到 Android 的 Unity 游戏。

在 Google Play 控制台中，我看到许多在旧 Android 版本 (<=7.1) 上发生的崩溃。崩溃是由 ClassNotFoundException 引起的，但报告没有显示未找到的类。

在崩溃控制台中，我得到以下堆栈跟踪：

java.lang.RuntimeException: 
  at android.app.ActivityThread.handleReceiver (ActivityThread.java:3025)
  at android.app.ActivityThread.-wrap18 (ActivityThread.java)
  at android.app.ActivityThread$H.handleMessage (ActivityThread.java:1565)
  at android.os.Handler.dispatchMessage (Handler.java:102)
  at android.os.Looper.loop (Looper.java:179)
  at android.app.ActivityThread.main (ActivityThread.java:6152)
  at java.lang.reflect.Method.invoke (Native Method)
  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run (ZygoteInit.java:886)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:776)
Caused by: java.lang.ClassNotFoundException: 
  at dalvik.system.BaseDexClassLoader.findClass (BaseDexClassLoader.java:56)
  at java.lang.ClassLoader.loadClass (ClassLoader.java:380)
  at java.lang.ClassLoader.loadClass (ClassLoader.java:312)
  at android.app.ActivityThread.handleReceiver (ActivityThread.java:3020)

这太通用了，并没有暗示缺少什么类。

我想知道是否有另一种方法可以找到丢失的课程。我正在使用 Multidex（我不知道它是否与问题有关）。

任何帮助将不胜感激在这里..

我很多天都在使用Netbeans.但突然间它开始给我跟随简单的hello程序的错误.

 java.lang.NoClassDefFoundError: newr
 Caused by: java.lang.ClassNotFoundException: newr
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:276)
at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
Exception in thread "main" Java Result: 1 
BUILD SUCCESSFUL (total time: 3 seconds)

这里是

我的编程是简单的你好程序

public class newr {
public static void main(String argv[]){
    System.out.println("hello");
}
}

它经常发生在我身上.我曾尝试卸载并再次安装它,但这并不能解决我的问题.我还尝试删除包含net bean缓存的.netbeans文件夹.但是每次它给我这样的错误时我都要删除这个.netbeans文件夹.有没有办法永久修复错误？我厌倦了删除缓存和卸载netbeans请帮助我....

当我运行以下代码片段连接到数据源以通过查询获取数据时:

        try {
        String driver = "com.microsoft.jdbc.sqlserver.SQLServerDriver";
        Class.forName(driver);
        String Url = "jdbc:sqlserver://localhost:1433;databaseName=movies";
        Connection connection = DriverManager.getConnection(Url,"sa", "xxxxxxx);
        //            Context initContext = new InitialContext();
        //            Context envContext = (Context)initContext.lookup("java:comp/env");
        //            DataSource ds = (DataSource)envContext.lookup("");
        //            Connection connection = ds.getConnection();
        String query_name = "select name from list where name='" + data + "'";

显示此异常跟踪:

java.lang.ClassNotFoundException: com.microsoft.jdbc.sqlserver.SQLServerDriver
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:276)
at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:169)
at gui.MainGui.startSqlServerDataSearch(MainGui.java:148)
at gui.MainGui$3.run(MainGui.java:129)
at java.lang.Thread.run(Thread.java:619) …

有时我的MR工作抱怨没有找到MyMapper类.而且我必须给job.setJarByClass(MyMapper.class); 告诉它从我的jar文件中加载它.

cloudera @cloudera-vm:/ tmp/translator $ hadoop jar MapReduceJobs.jar translator/input/Portuguese.txt translator/output 13/06/13 03:36:57 WARN mapred.JobClient:没有作业jar文件集.可能找不到用户类.请参阅JobConf(Class)或JobConf#setJar(String).13/06/13 03:36:57 INFO input.FileInputFormat:要处理的总输入路径:1 13/06/13 03:36:57 INFO mapred.JobClient:正在运行的工作:job_201305100422_0043 13/06/13 03:36: 58 INFO mapred.JobClient:map 0%reduce 0%13/06/13 03:37:03 INFO mapred.JobClient:Task Id:attempt_201305100422_0043_m_000000_0,Status:FAILED java.lang.RuntimeException:java.lang.ClassNotFoundException:com.mapreduce .variousformats.keyvaluetextinputformat.MyMapper at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:996)org.apache.hadoop.mapreduce.JobContext.getMapperClass(JobContext.java:

问题:为什么会这样.为什么不总是告诉我从我的jar文件中加载它.是否有一些解决这类问题的最佳实践.此外,如果我使用一些第三方库,我也必须为他们这样做.

似乎有许多与此相关的类似问题,但没有一个能够为我提供任何帮助.我在SQL Server上运行Microsoft的JDBC驱动程序 (我正在使用)并使用集成身份验证来访问我的数据库.用于连接的代码段如下:sqljdbc4.jar

String connectionUrl="jdbc:sqlserver://servername:1433;integratedSecurity=true;";

try {
    Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
    con = DriverManager.getConnection(connectionUrl);
}//catch, etc...

当我在Eclipse中运行项目时,它会毫无障碍地启动.当我运行Maven clean install并将其打包到.jar中时,我收到错误:

java.lang.ClassNotFoundException: Failure to load: com.microsoft.sqlserver.jdbc.SQLServerDriver
    at launch.JarClassLoader.loadClass(JarClassLoader.java:964)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Unknown Source)
    at ui.SearchWindow$1.run(SearchWindow.java:97)
    at java.awt.event.InvocationEvent.dispatch(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$200(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source) …

我在每个支持设计小部件上都出错。像recyclerview，协调器布局等。每次，我添加一个正在显示的支持设计小部件。

java.lang.ClassNotFoundException: android.view.View$OnUnhandledKeyEventListener

在布局问题部分。我正在使用api 28.0.0-rc01，gradle 4.4 android 3.1.4。这是我的build.gradle（app）文件

    apply plugin: 'com.android.application'

android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "com.example.android.test5test"
        minSdkVersion 23
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
    buildToolsVersion '28.0.2'
    productFlavors {
    }
}

dependencies {
    implementation fileTree(include: ['*.jar'], dir: 'libs')
    implementation 'com.android.support:appcompat-v7:28.0.0-rc01'
    implementation 'com.android.support.constraint:constraint-layout:1.1.2'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
    implementation 'com.android.support:design:28.0.0-rc01'
    implementation 'com.android.support:cardview-v7:28.0.0-rc01'
    implementation 'com.android.support:recyclerview-v7:28.0.0-rc01'
}

这是我的布局文件

<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent" …