java.sql.SQLException嘗試在Oracle中計數行時

Question

我在Java託管bean中遇到了一個我找不到的問題。

import java.io.Serializable; 
import javax.enterprise.context.SessionScoped; 
// or import javax.faces.bean.SessionScoped; 
import javax.inject.Named; 
/* 
* include SQL Packages 
*/ 
import java.sql.Connection; 
import java.sql.PreparedStatement; 
import java.sql.ResultSet; 
import java.sql.SQLException; 
import java.util.HashMap; 
import javax.annotation.PostConstruct; 
import javax.sql.DataSource; 
import javax.annotation.Resource; 
import javax.faces.bean.ViewScoped; 
// or import javax.faces.bean.ManagedBean; 

import org.glassfish.osgicdi.OSGiService; 

import org.primefaces.model.chart.CartesianChartModel; 
import org.primefaces.model.chart.ChartSeries; 

@Named("DashboardController") 
@SessionScoped 
public class Dashboard implements Serializable 
{ 

    /* 
    * Call the Oracle JDBC Connection driver 
    */ 
    @Resource(name = "jdbc/Oracle") 
    private DataSource ds; 
    private CartesianChartModel categoryModel; 

    public Dashboard() throws SQLException 
    { 
     createCategoryModel(); 
    } 

    public CartesianChartModel getCategoryModel() 
    { 
     return categoryModel; 
    } 

    private void createCategoryModel() throws SQLException 
    { 
     categoryModel = new CartesianChartModel(); 

     // Active Accounts 

     ChartSeries ActiveAccounts = new ChartSeries(); 
     ActiveAccounts.setLabel("Active Accounts"); 

     ActiveAccounts.set("Active Accounts", CheckDataDB("USERS","USERSTATUS","Active")); 

     categoryModel.addSeries(ActiveAccounts); 

     // Blocked Accounts 

     ChartSeries BlockedAccounts = new ChartSeries(); 
     BlockedAccounts.setLabel("Blocked Accounts"); 

     BlockedAccounts.set("Blocked Accounts", CheckDataDB("USERS","USERSTATUS","Blocked")); 

     categoryModel.addSeries(BlockedAccounts); 

     // Active Groups 

     ChartSeries ActiveGroups = new ChartSeries(); 
     ActiveGroups.setLabel("Active Groups"); 

     ActiveGroups.set("Active Groups", CheckDataDB("GROUPS","GROUPSTATUS","Active")); 

     categoryModel.addSeries(ActiveGroups); 

     // Blocked Groups 

     ChartSeries BlockedGroups = new ChartSeries(); 
     BlockedGroups.setLabel("Blocked Groups"); 

     BlockedGroups.set("Blocked Groups", CheckDataDB("GROUPS","GROUPSTATUS","Blocked")); 

     categoryModel.addSeries(BlockedGroups); 



    } 

    // Database data 

    public int CheckDataDB(String DBtablename, String DBStatus, String DBArgument) throws SQLException { 

     int count = 0; 
     String SQLStatement = null; 

     if (ds == null) { 
      throw new SQLException(); 
     } 

     Connection conn = ds.getConnection(); 
     if (conn == null) { 
      throw new SQLException(); 
     } 

     PreparedStatement ps = null; 

     try { 
      conn.setAutoCommit(false); 
      boolean committed = false; 
      try { 
       SQLStatement = "SELECT count(*) FROM ? WHERE ? = ?"; 

       ps = conn.prepareStatement(SQLStatement); 
       ps.setString(1, DBtablename); 
       ps.setString(2, DBStatus);     
       ps.setString(3, DBArgument); 

       ResultSet result = ps.executeQuery(); 

       if (result.next()) { 
        count = result.getInt(1); 
       } 

       conn.commit(); 
       committed = true; 
      } finally { 
       if (!committed) { 
        conn.rollback(); 
       } 
      } 
     } finally { 
      /* Release the resources */ 
      ps.close(); 
      conn.close(); 
     } 

     return count; 
    } 
} 

當我嘗試運行代碼，我得到這個錯誤堆棧：

com.sun.faces.mgbean.ManagedBeanCreationException: Cant instantiate class: com.DX_57.AC_57.Dashboard. 
    at com.sun.faces.mgbean.BeanBuilder.newBeanInstance(BeanBuilder.java:193) 
    at com.sun.faces.mgbean.BeanBuilder.build(BeanBuilder.java:102) 
    at com.sun.faces.mgbean.BeanManager.createAndPush(BeanManager.java:409) 
    at com.sun.faces.mgbean.BeanManager.create(BeanManager.java:269) 
    at com.sun.faces.el.ManagedBeanELResolver.resolveBean(ManagedBeanELResolver.java:244) 
    at com.sun.faces.el.ManagedBeanELResolver.getValue(ManagedBeanELResolver.java:116) 
    at com.sun.faces.el.DemuxCompositeELResolver._getValue(DemuxCompositeELResolver.java:176) 
    at com.sun.faces.el.DemuxCompositeELResolver.getValue(DemuxCompositeELResolver.java:203) 
    at com.sun.el.parser.AstIdentifier.getValue(AstIdentifier.java:103) 
    at com.sun.el.parser.AstValue.getValue(AstValue.java:179) 
    at com.sun.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:224) 
    at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:109) 
    at javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:194) 
    at org.primefaces.component.chart.UIChart.getValue(UIChart.java:75) 
    at org.primefaces.component.chart.bar.BarChartRenderer.encodeOptions(BarChartRenderer.java:62) 
    at org.primefaces.component.chart.bar.BarChartRenderer.encodeScript(BarChartRenderer.java:51) 
    at org.primefaces.component.chart.bar.BarChartRenderer.encodeEnd(BarChartRenderer.java:36) 
    at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:875) 
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1786) 
    at javax.faces.render.Renderer.encodeChildren(Renderer.java:168) 
    at javax.faces.component.UIComponentBase.encodeChildren(UIComponentBase.java:845) 
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1779) 
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782) 
    at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1782) 
    at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:424) 
    at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:125) 
    at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:121) 
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101) 
    at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139) 
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:594) 
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1550) 
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:281) 
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175) 
    at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655) 
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595) 
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:161) 
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:331) 
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231) 
    at com.sun.enterprise.v3.services.impl.ContainerMapper$AdapterCallable.call(ContainerMapper.java:317) 
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:195) 
    at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:860) 
    at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:757) 
    at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1056) 
    at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:229) 
    at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137) 
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104) 
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90) 
    at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79) 
    at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54) 
    at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59) 
    at com.sun.grizzly.ContextTask.run(ContextTask.java:71) 
    at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532) 
    at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513) 
    at java.lang.Thread.run(Thread.java:722) 
Caused by: java.sql.SQLException 
    at com.DX_57.AC_57.Dashboard.CheckDataDB(Dashboard.java:116) 
    at com.DX_57.AC_57.Dashboard.createCategoryModel(Dashboard.java:73) 
    at com.DX_57.AC_57.Dashboard.<init>(Dashboard.java:56) 
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) 
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57) 
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) 
    at java.lang.reflect.Constructor.newInstance(Constructor.java:525) 
    at java.lang.Class.newInstance0(Class.java:372) 
    at java.lang.Class.newInstance(Class.java:325) 
    at com.sun.faces.mgbean.BeanBuilder.newBeanInstance(BeanBuilder.java:188) 
    ... 53 more 

你能幫我解決這個問題？我想使用一種Java方法來對代碼進行更緊湊的計數。

Answer 1

什麼行不通是下面這段代碼設置列給PreparedStatement的表名的名稱的現行辦法：

String SQLStatement = null; 
... 
SQLStatement = "SELECT count(*) FROM ? WHERE ? = ?"; 
ps = conn.prepareStatement(SQLStatement); 
ps.setString(1, DBtablename); 
ps.setString(2, DBStatus);     
ps.setString(3, DBArgument); 

原因是準備語句應該以語法正確的SQL構造（和通常是參數），然後設置參數值。 setString(int, String)不是將SQL語句粘貼在一起的通用工具，它是爲參數設置值。

什麼工作是類似以下內容（作爲一個快速修復這個代碼，還不如好的樣式的任何爲例）：

//first we construct reasonable SQL statement with one parameter 
SQLStatement = "SELECT count(*) FROM "+DBtablename+ " WHERE "+DBStatus+"=?"; 
//then we set value for parameter 
ps.setString(1, DBArgument); 

Answer 2

您不必SQLException的問題happeny早得多：

com.sun.faces.mgbean.ManagedBeanCreationException: Cant instantiate class: com.DX_57.AC_57.Dashboard. 

那是你的異常來搜索。