我正在使用spring4 + maven + mysql编写一个web项目。我写了一个像这样的jdbcUtil：
public class JdbcUtils {
private static String driver = null;
private static String url = null;
private static String username = null;
private static String password = null;
static{
try{
InputStream in = JdbcUtils.class.getClassLoader().getResourceAsStream("db.properties");
Properties prop = new Properties();
prop.load(in);
driver = prop.getProperty("driver");
url = prop.getProperty("url");
username = prop.getProperty("username");
password = prop.getProperty("password");
Class.forName(driver);
}catch (Exception e) {
e.printStackTrace();
throw new ExceptionInInitializerError(e);
}
}
public static Connection getConnection() throws SQLException{
return DriverManager.getConnection(url, username,password);
}
public static void release(Connection conn,Statement st,ResultSet rs){
if(rs!=null){
try{
rs.close();
}catch (Exception e) {
e.printStackTrace();
}
rs = null;
}
if(st!=null){
try{
st.close();
}catch (Exception e) {
e.printStackTrace();
}
}
if(conn!=null){
try{
conn.close();
}catch (Exception e) {
e.printStackTrace();
}
}
}
}
和像这样的jdbc测试类：
public class JdbcCRUDByPreparedStatement {
@Test
public void insert(){
Connection conn = null;
PreparedStatement st = null;
ResultSet rs = null;
try{
conn = JdbcUtils.getConnection();
String sql = "insert into users(id,name,password,email,school,authority,technical,telenumber) values(?,?,?,?,?,?,?,?)";
st = conn.prepareStatement(sql);
st.setInt(1, 1);
st.setString(2, "xiaoming");
st.setString(3, "root");
st.setString(4, "939712464@qq.com");
st.setString(5, "nanjing");
st.setInt(6, 0);
st.setString(7, "javaweb");
st.setInt(8, 123456);
int num = st.executeUpdate();
if(num>0){
System.out.println("insert success!");
}
}catch (Exception e) {
e.printStackTrace();
}finally{
//SQL执行完成之后释放相关资源
JdbcUtils.release(conn, st, rs);
}
}
@Test
public void delete(){
Connection conn = null;
PreparedStatement st = null;
ResultSet rs = null;
try{
conn = JdbcUtils.getConnection();
String sql = "delete from users where id=?";
st = conn.prepareStatement(sql);
st.setInt(1, 1);
int num = st.executeUpdate();
if(num>0){
System.out.println("delete success");
}
}catch (Exception e) {
e.printStackTrace();
}finally{
JdbcUtils.release(conn, st, rs);
}
}
@Test
public void update(){
Connection conn = null;
PreparedStatement st = null;
ResultSet rs = null;
try{
conn = JdbcUtils.getConnection();
String sql = "update users set name=?,email=? where id=?";
st = conn.prepareStatement(sql);
st.setString(1, "gacl");
st.setString(2, "gacl@sina.com");
st.setInt(3, 2);
int num = st.executeUpdate();
if(num>0){
System.out.println("update success!");
}
}catch (Exception e) {
e.printStackTrace();
}finally{
JdbcUtils.release(conn, st, rs);
}
}
@Test
public void find(){
Connection conn = null;
PreparedStatement st = null;
ResultSet rs = null;
try{
conn = JdbcUtils.getConnection();
String sql = "select * from users where id=?";
st = conn.prepareStatement(sql);
st.setInt(1, 1);
rs = st.executeQuery();
if(rs.next()){
System.out.println(rs.getString("name"));
}
}catch (Exception e) {
}finally{
JdbcUtils.release(conn, st, rs);
}
}
}
但是当我作为Junite测试运行时，它无法成功运行，failuer trace：
java.lang.NullPointerException
at java.util.Properties$LineReader.readLine(Properties.java:434)
at java.util.Properties.load0(Properties.java:353)
at java.util.Properties.load(Properties.java:341)
at me.gacl.util.JdbcUtils.<clinit>(JdbcUtils.java:22)
at me.gacl.jdbc.JdbcCRUDByPreparedStatement.delete(JdbcCRUDByPreparedStatement.java:54)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
任何人都知道如何修复它？
答案 0 :(得分：0)
检查结果：
InputStream in = JdbcUtils.class.getClassLoader()
.getResourceAsStream("db.properties");
如果找不到资源db.properties，您将收到null，这会导致您的例外：
prop.load(in);
Class.getResourceAsStream()的Javadoc声明：
返回： InputStream对象;如果找不到具有此名称的资源，则返回null
如果您的资源db.properties与您的班级JdbcUtils位于同一个套餐中，则"db.properties"是正确的参考。否则，如果资源db.properties位于其他位置，则必须使用前导/来定义路径，例如"/db.properties"表示类路径的根。
答案 1 :(得分：0)
NoClassDefFoundError意味着该类在编译时存在于类路径中，但在运行时的类路径中不存在。