I created a class that gets an instance of a Database connection. However I am getting an error saying the calling class is null. I will post my error below.
Now I have a working and non working version of this code. I first just jammed everything into a single class to get it up and running then started to clean it up which is when I ran into issues.
This class "createJobTicket" calls the instance of DataBaseConnectionDAO
public class createJobTicket {
//private java.sql.Connection conn = null;
//private java.sql.Statement stmt = null;
private static DataBaseConnectionDAO databaseConnection = DataBaseConnectionDAO.getInstance();
public static HSSFWorkbook getWorkbook(HSSFWorkbook workbook, Long id, Environment env){
try{
java.sql.Connection conn = databaseConnection.getConnection();
java.sql.Statement stmt = conn.createStatement();
String sql;
sql = "SELECT"
+" hillcresttooldie.T_PO.id po_id,"
+" hillcresttooldie.T_PO.DUE_DATE due_date,"
+" hillcresttooldie.T_CUSTOMER.CUSTOMER_NAME customer_name,"
+" hillcresttooldie.T_PART.ID part_id,"
+" hillcresttooldie.T_PO_PART.PART_QUANTITY part_quantity,"
+" hillcresttooldie.T_PART.PART_NUMBER part_number,"
+" hillcresttooldie.T_PART.PART_DESCRIPTION part_description,"
+" hillcresttooldie.T_PART.PLASMA_HRS_PER_PART plasma_hrs,"
+" hillcresttooldie.T_PART.GRIND_HRS_PER_PART grind_hrs,"
+" hillcresttooldie.T_PART.MILL_HRS_PER_PART mill_hrs,"
+" hillcresttooldie.T_PART.BRAKEPRESS_HRS_PER_PART brakepress_hrs,"
+" hillcresttooldie.T_PART.LASER_HRS_PER_PART laser_hrs,"
+" hillcresttooldie.T_MATERIAL.MATERIAL_THICKNESS material_thickness"
+" FROM hillcresttooldie.T_PO"
+" join hillcresttooldie.T_PO_PART"
+" on hillcresttooldie.T_PO_PART.PO_ID = hillcresttooldie.T_PO.ID"
+" join hillcresttooldie.T_PART"
+" on hillcresttooldie.T_PART.ID = hillcresttooldie.T_PO_PART.PART_ID"
+" join hillcresttooldie.T_CUSTOMER"
+" on hillcresttooldie.T_PO.CUSTOMER_ID = hillcresttooldie.T_CUSTOMER.ID"
+" join hillcresttooldie.T_PART_MATERIAL"
+" on hillcresttooldie.T_PART.ID = hillcresttooldie.T_PART_MATERIAL.PARTS_ID"
+" join hillcresttooldie.T_MATERIAL"
+" on hillcresttooldie.T_PART_MATERIAL.materials_id = hillcresttooldie.T_MATERIAL.id"
+" where T_PO.id = '"+id+"'";
ResultSet rs = stmt.executeQuery(sql);
int index = 0;
//STEP 5: Extract data from result set
while(rs.next()){
int po_id = rs.getInt("po_id");
String due_date = rs.getString("due_date");
String customer_name = rs.getString("customer_name");
int part_id = rs.getInt("part_id");
int part_quantity = rs.getInt("part_quantity");
String part_number = rs.getString("part_number");
String part_description = rs.getString("part_description");
BigDecimal plasma_hrs = rs.getBigDecimal("plasma_hrs");
BigDecimal grind_hrs = rs.getBigDecimal("grind_hrs");
BigDecimal mill_hrs = rs.getBigDecimal("mill_hrs");
BigDecimal brakepress_hrs = rs.getBigDecimal("brakepress_hrs");
BigDecimal laser_hrs = rs.getBigDecimal("laser_hrs");
double material_thickness = rs.getDouble("material_thickness");
//Create the Sheet
String sheetName = index + "-" + customer_name + "-" + part_number;
HSSFSheet sheet = workbook.createSheet(sheetName);
//Apply Template to the sheet
generateTemplate.applyTemplate(workbook, sheet);
sheet.getRow(1).createCell(1).setCellValue(po_id);
sheet.getRow(5).getCell(3).setCellValue(customer_name);
sheet.getRow(5).createCell(8).setCellValue(due_date);
sheet.getRow(6).getCell(3).setCellValue(part_number);
sheet.getRow(6).createCell(8).setCellValue(part_quantity);
sheet.getRow(7).createCell(4).setCellValue(part_description);
sheet.getRow(7).createCell(8).setCellValue(material_thickness);
index++;
}
//STEP 6: Clean-up environment
rs.close();
stmt.close();
conn.close();
}catch(SQLException se){
se.printStackTrace();
System.out.println("SQL Exeception thrown");
}catch(Exception e){
e.printStackTrace();
}//end try
return workbook;
}
You can notice that the following is commented out:
//private java.sql.Connection conn = null;
//private java.sql.Statement stmt = null;
This is because if I my IDE said:
Cannot make a static reference to the non-static field conn
Cannot make a static reference to the non-static field stmt
My DataBaseConnectionDAO looks like the following:
public class DataBaseConnectionDAO {
@Inject
private static Environment env;
private static DataBaseConnectionDAO instance;
// Step 1: JDBC props
String DB_URL = env.getProperty("spring.datasource.url");
String USER = env.getProperty("spring.datasource.username");
String PASS = env.getProperty("spring.datasource.password");
java.sql.Connection conn = null;
java.sql.Statement stmt = null;
private DataBaseConnectionDAO() { }
public static DataBaseConnectionDAO getInstance() {
if (instance == null) {
synchronized (DataBaseConnectionDAO.class) {
if (instance == null) {
instance = new DataBaseConnectionDAO();
}
}
}
return instance;
}
public java.sql.Connection getConnection() throws ClassNotFoundException,
SQLException {
Class.forName("com.mysql.jdbc.Driver");
if (conn == null) {
conn = DriverManager.getConnection(DB_URL, USER, PASS);
}
return conn;
}
}
[DEBUG] com.htd.aop.logging.LoggingAspect - Enter: com.htd.web.rest.PoResource.generateJobTicket() with argument[s] = [16, com.codahale.metrics.servlet.AbstractInstrumentedFilter$StatusExposingServletResponse@1424a144]
[ERROR] com.htd.aop.logging.LoggingAspect - Exception in com.htd.web.rest.PoResource.generateJobTicket() with cause = null
java.lang.NoClassDefFoundError: Could not initialize class com.htd.web.rest.util.createJobTicket
at com.htd.web.rest.PoResource.generateJobTicket(PoResource.java:332) ~[classes/:na]
at com.htd.web.rest.PoResource$$FastClassBySpringCGLIB$$cfcd338a.invoke(<generated>) ~[spring-core-4.1.6.RELEASE.jar:na]
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204) ~[spring-core-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:717) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:85) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at com.htd.aop.logging.LoggingAspect.logAround(LoggingAspect.java:49) ~[classes/:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_31]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_31]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_31]
at java.lang.reflect.Method.invoke(Method.java:483) ~[na:1.8.0_31]
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:621) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:610) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:68) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.aop.aspectj.AspectJAfterThrowingAdvice.invoke(AspectJAfterThrowingAdvice.java:58) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:653) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at com.htd.web.rest.PoResource$$EnhancerBySpringCGLIB$$4795e29.generateJobTicket(<generated>) [spring-core-4.1.6.RELEASE.jar:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_31]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_31]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_31]
at java.lang.reflect.Method.invoke(Method.java:483) ~[na:1.8.0_31]
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:137) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110) [spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:776) [spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:705) [spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) [spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959) [spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893) [spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966) [spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:857) [spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:618) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842) [spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:725) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) [tomcat-embed-websocket-8.0.20.jar:8.0.20]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.20.jar:8.0.20]
at com.codahale.metrics.servlet.AbstractInstrumentedFilter.doFilter(AbstractInstrumentedFilter.java:104) [metrics-servlet-3.1.1.jar:3.1.1]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.springframework.boot.actuate.autoconfigure.EndpointWebMvcAutoConfiguration$ApplicationContextHeaderFilter.doFilterInternal(EndpointWebMvcAutoConfiguration.java:291) [spring-boot-actuator-1.2.3.RELEASE.jar:1.2.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:316) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:126) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:90) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:114) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:122) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.authentication.rememberme.RememberMeAuthenticationFilter.doFilter(RememberMeAuthenticationFilter.java:157) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:168) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:48) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:205) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:120) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) [spring-security-web-4.0.0.RELEASE.jar:na]
at com.htd.web.filter.CsrfCookieGeneratorFilter.doFilterInternal(CsrfCookieGeneratorFilter.java:34) [classes/:na]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.csrf.CsrfFilter.doFilterInternal(CsrfFilter.java:96) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:64) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:91) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:53) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:213) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:176) [spring-security-web-4.0.0.RELEASE.jar:na]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.springframework.boot.actuate.trace.WebRequestTraceFilter.doFilterInternal(WebRequestTraceFilter.java:102) [spring-boot-actuator-1.2.3.RELEASE.jar:1.2.3.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:85) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:516) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1086) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:659) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:223) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1558) [tomcat-embed-core-8.0.20.jar:8.0.20]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1515) [tomcat-embed-core-8.0.20.jar:8.0.20]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_31]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_31]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.0.20.jar:8.0.20]
at java.lang.Thread.run(Thread.java:745) [na:1.8.0_31]
error:
[DEBUG] com.htd.aop.logging.LoggingAspect - Enter: com.htd.web.rest.PoResource.generateJobTicket() with argument[s] = [16, com.codahale.metrics.servlet.AbstractInstrumentedFilter$StatusExposingServletResponse@613cf2e]
[ERROR] com.htd.aop.logging.LoggingAspect - Exception in com.htd.web.rest.PoResource.generateJobTicket() with cause = null
java.lang.NoClassDefFoundError: Could not initialize class com.htd.web.rest.util.createJobTicket
at com.htd.web.rest.PoResource.generateJobTicket(PoResource.java:332) ~[classes/:na]
at com.htd.web.rest.PoResource$$FastClassBySpringCGLIB$$cfcd338a.invoke(<generated>) ~[spring-core-4.1.6.RELEASE.jar:na]
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204) ~[spring-core-4.1.6.RELEASE.jar:4.1.6.RELEASE]
答案 0 :(得分：2)
您首先需要了解此错误消息的含义：
java.lang.NoClassDefFoundError: Could not initialize class com.htd.web.rest.util.createJobTicket
当JVM加载一个类时，它将完成该类的任何静态初始化，即分配给static个字段的任何值并运行任何static { ... }块。由于这涉及运行Java代码，此过程可能会导致抛出异常。如果在类的静态初始化期间抛出异常，则类加载将失败。 Java会将异常包装在ExceptionInInitializerError中并抛出它。如果您再次尝试加载同一个类，Java将断然拒绝加载它，而是抛出NoClassDefFoundError消息Could not initialize class ...。
由于这是您看到的错误，我只能断定您的createJobTicket类未通过静态初始化，并且上面的异常堆栈跟踪不是从您第一次尝试使用{{1 } .class。例如，如果您的应用程序是Web应用程序，请尝试重新启动Web应用程序容器，再次尝试并查看是否第一次出现不同的错误。
createJobTicket类的静态初始化如下：
createJobTicket因此，您的 private static DataBaseConnectionDAO databaseConnection = DataBaseConnectionDAO.getInstance();
方法必须抛出异常。
避免这种静态初始化问题的最佳方法是完全避免静态初始化。例如，在下文中，我们创建一个方法DataBaseConnectionDAO.getInstance()，如果尚未设置getDatabaseConnection()字段，则设置databaseConnection字段，并另外调用DAO以返回JDBC Connection对象：
private static DataBaseConnectionDAO databaseConnection;
private static java.sql.Connection getDatabaseConnection() {
if (databaseConnection == null) {
databaseConnection = DataBaseConnectionDAO.getInstance();
}
return databaseConnection.getConnection();
}
public static HSSFWorkbook getWorkbook(HSSFWorkbook workbook, Long id, Environment env){
try{
java.sql.Connection conn = getDatabaseConnection();
// ...
此方法应该阻止您的createJobTicket类无法完成静态初始化。但是，请不要指望您的代码在执行此操作后立即开始工作。上面的更改无法修复导致静态初始化失败的异常。它所做的只是确保在静态初始化类之后才抛出此异常。如果您随后尝试运行代码，则应该希望在日志中看到实际的异常，而不是NoClassDefFoundError。
那么，为什么你的DataBaseConnectionDAO.getInstance()方法会抛出异常呢？我最好的猜测是：
@Inject
private static Environment env;
一些搜索表明您无法使用Spring将值注入此类静态字段中，因此您可能会在null的环境中查找值时遇到NullPointerException。但是，我还没有充分考虑到这一点，所以我不能保证这实际上是问题所在。