我在Java托管bean中遇到了一个我无法找到的问题。
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;
}
}
当我尝试运行代码时，我得到了这个错误堆栈：
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
你能帮我解决问题吗？我想使用一种Java方法来使代码更紧凑来计算行数。
答案 0 :(得分：3)
在下面的代码片段中，当前的方法是将表名和列名设置为PreparedStatement：
String SQLStatement = null;
...
SQLStatement = "SELECT count(*) FROM ? WHERE ? = ?";
ps = conn.prepareStatement(SQLStatement);
ps.setString(1, DBtablename);
ps.setString(2, DBStatus);
ps.setString(3, DBArgument);
原因是准备好的语句应该使用语法正确的SQL（通常是参数）来构造，然后应该设置参数的值。 setString(int, String)不是将SQL语句粘合在一起的通用工具，而是用于为参数设置值。
什么会起作用如下（作为对此代码的快速修复，而不是任何良好风格的示例）：
//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);
答案 1 :(得分：1)
你没有SQLException这个问题早就发生了：
com.sun.faces.mgbean.ManagedBeanCreationException: Cant instantiate class: com.DX_57.AC_57.Dashboard.
这是你的例外搜索。