我正在尝试实现本教程中的代码：
这是托管bean：
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.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import javax.annotation.PostConstruct;
import javax.sql.DataSource;
import javax.annotation.Resource;
import javax.faces.bean.ViewScoped;
import javax.faces.component.UICommand;
import javax.faces.context.FacesContext;
import javax.inject.Inject;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
// or import javax.faces.bean.ManagedBean;
import javax.faces.event.ActionEvent;
import org.glassfish.osgicdi.OSGiService;
// source http://balusc.blogspot.com/2008/10/effective-datatable-paging-and-sorting.html
@Named("SessionsController")
@ViewScoped
public class Sessions implements Serializable {
/* Call the Oracle JDBC Connection driver */
@Resource(name = "jdbc/Oracle")
private DataSource ds;
// Data.
private List<ActiveSessionObj> dataList;
private int totalRows;
// Paging.
private int firstRow;
private int rowsPerPage;
private int totalPages;
private int pageRange;
private Integer[] pages;
private int currentPage;
// Sorting.
private String sortField;
private boolean sortAscending;
/* Constructor */
public Sessions() {
/* Set default properties */
rowsPerPage = 10; // Default rows per page (max amount of rows to be displayed at once).
pageRange = 10; // Default page range (max amount of page links to be displayed at once).
sortField = "ASESSIONID"; // Default sort field.
sortAscending = true; // Default sort direction.
}
private static class ActiveSessionObj {
/* Oracle table structure
CREATE TABLE ACTIVESESSIONSLOG(
ASESSIONID VARCHAR2(30 ) NOT NULL,
USERID VARCHAR2(30 ),
ACTIVITYSTART TIMESTAMP(6),
ACTIVITYEND TIMESTAMP(6),
ACTIVITY CLOB
)
*/
private String aSessionID;
private String userID;
private Date activityStart;
private Date activityEnd;
private String activity;
public ActiveSessionObj(String aSessionID, String userID, Date activityStart, Date activityEnd, String activity) {
this.aSessionID = aSessionID;
this.userID = userID;
this.activityStart = activityStart;
this.activityEnd = activityEnd;
this.activity = activity;
}
public String getaSessionID() {
return aSessionID;
}
public void setaSessionID(String aSessionID) {
this.aSessionID = aSessionID;
}
public String getactivity() {
return activity;
}
public void setactivity(String activity) {
this.activity = activity;
}
public Date getactivityEnd() {
return activityEnd;
}
public void setactivityEnd(Date activityEnd) {
this.activityEnd = activityEnd;
}
public Date getactivityStart() {
return activityStart;
}
public void setactivityStart(Date activityStart) {
this.activityStart = activityStart;
}
public String getuserID() {
return userID;
}
public void setuserID(String userID) {
this.userID = userID;
}
private ActiveSessionObj() {
throw new UnsupportedOperationException("Not yet implemented");
}
}
// Paging actions -----------------------------------------------------------------------------
public void pageFirst() {
page(0);
}
public void pageNext() {
page(firstRow + rowsPerPage);
}
public void pagePrevious() {
page(firstRow - rowsPerPage);
}
public void pageLast() {
page(totalRows - ((totalRows % rowsPerPage != 0) ? totalRows % rowsPerPage : rowsPerPage));
}
public void page(ActionEvent event) {
page(((Integer) ((UICommand) event.getComponent()).getValue() - 1) * rowsPerPage);
}
private void page(int firstRow) {
this.firstRow = firstRow;
loadDataList(); // Load requested page.
}
// Sorting actions ----------------------------------------------------------------------------
public void sort(ActionEvent event) {
String sortFieldAttribute = (String) event.getComponent().getAttributes().get("sortField");
// If the same field is sorted, then reverse order, else sort the new field ascending.
if (sortField.equals(sortFieldAttribute)) {
sortAscending = !sortAscending;
} else {
sortField = sortFieldAttribute;
sortAscending = true;
}
pageFirst(); // Go to first page and load requested page.
}
// Loaders ------------------------------------------------------------------------------------
private void loadDataList() {
// Load list and totalCount.
try {
dataList = list(firstRow, rowsPerPage, sortField, sortAscending);
totalRows = countDBRowNum(); //count the tablerows
} catch (Exception e) {
throw new RuntimeException(e);
}
// Set currentPage, totalPages and pages.
currentPage = (totalRows / rowsPerPage) - ((totalRows - firstRow) / rowsPerPage) + 1;
totalPages = (totalRows / rowsPerPage) + ((totalRows % rowsPerPage != 0) ? 1 : 0);
int pagesLength = Math.min(pageRange, totalPages);
pages = new Integer[pagesLength];
// firstPage must be greater than 0 and lesser than totalPages-pageLength.
int firstPage = Math.min(Math.max(0, currentPage - (pageRange / 2)), totalPages - pagesLength);
// Create pages (page numbers for page links).
for (int i = 0; i < pagesLength; i++) {
pages[i] = ++firstPage;
}
}
// Getters ------------------------------------------------------------------------------------
public List<ActiveSessionObj> getdataList() {
if (dataList == null) {
loadDataList(); // Preload page for the 1st view.
}
return dataList;
}
public int getTotalRows() {
return totalRows;
}
public int getFirstRow() {
return firstRow;
}
public int getRowsPerPage() {
return rowsPerPage;
}
public Integer[] getPages() {
return pages;
}
public int getCurrentPage() {
return currentPage;
}
public int getTotalPages() {
return totalPages;
}
// Setters ------------------------------------------------------------------------------------
public void setRowsPerPage(int rowsPerPage) {
this.rowsPerPage = rowsPerPage;
}
// Actions ------------------------------------------------------------------------------------
/**
* Returns list of ActiveSessionObj items starting at the given first index with the given row count,
* sorted by the given sort field and sort order.
* @param firstRow First index of rows to be returned.
* @param rowCount Amount of rows to be returned.
* @param sortField Field to sort the data on.
* @param sortAscending Whether to sort data ascending or not.
* @return list of ActiveSessionObj items starting at the given first index with the given row count,
* sorted by the given sort field and sort order.
* @throws DAOException If something fails at DAO level.
*/
public List<ActiveSessionObj> list(int firstRow, int rowCount, String sortField, boolean sortAscending) throws SQLException {
String SqlStatement = null;
if (ds == null) {
throw new SQLException();
}
Connection conn = ds.getConnection();
if (conn == null) {
throw new SQLException();
}
String sortDirection = sortAscending ? "ASC" : "DESC";
SqlStatement = "SELECT * FROM ACTIVESESSIONSLOG WHERE ROWNUM >= ? AND ROWNUM <= ? ORDER BY %s %s";
String sql = String.format(SqlStatement, sortField, sortDirection);
PreparedStatement ps = null;
ResultSet resultSet = null;
List<ActiveSessionObj> dataList = new ArrayList<ActiveSessionObj>();
try {
conn.setAutoCommit(false);
boolean committed = false;
try {
ps = conn.prepareStatement(sql);
ps.setInt(1, firstRow);
ps.setInt(2, rowCount);
resultSet = ps.executeQuery();
/* take the result from the SQL query and insert it into Array List collection */
dataList = ActiveSessionsArrayList(resultSet);
conn.commit();
committed = true;
} finally {
if (!committed) {
conn.rollback();
}
}
} finally {
ps.close();
conn.close();
}
return dataList;
}
/**
* Returns total amount of rows in table.
* @return Total amount of rows in table.
* @throws DAOException If something fails at DAO level.
*/
public int countDBRowNum() throws Exception {
String SqlStatement = null;
if (ds == null) {
throw new SQLException();
}
Connection conn = ds.getConnection();
if (conn == null) {
throw new SQLException();
}
SqlStatement = "SELECT count(*) FROM ACTIVESESSIONSLOG";
PreparedStatement ps = null;
ResultSet resultSet = null;
int count = 0;
try {
conn.setAutoCommit(false);
boolean committed = false;
try {
SqlStatement = "SELECT count(*) FROM ACTIVESESSIONSLOG";
ps = conn.prepareStatement(SqlStatement);
resultSet = ps.executeQuery();
if (resultSet.next()) {
count = resultSet.getInt(1);
}
conn.commit();
committed = true;
} finally {
if (!committed) {
conn.rollback();
}
}
} finally {
ps.close();
conn.close();
}
return count;
}
/**
* Map the current row of the given ResultSet to ActiveSessionObj.
* @param resultSet The ResultSet of which the current row is to be mapped to ActiveSessionObj.
* @return The mapped ActiveSessionObj from the current row of the given ResultSet.
* @throws SQLException If something fails at database level.
*/
private static ArrayList<ActiveSessionObj> ActiveSessionsArrayList(ResultSet rs) throws SQLException {
ArrayList<ActiveSessionObj> al = null;
try {
while (rs.next()) {
al.add(new ActiveSessionObj(
rs.getString("ASESSIONID"),
rs.getString("USERID"),
timestampToDate(rs.getTimestamp("ACTIVITYSTART")),
timestampToDate(rs.getTimestamp("ACTIVITYEND")),
rs.getString("ACTIVITY")));
}
} catch (Exception x) {
x.printStackTrace();
}
return al;
/*
CREATE TABLE ACTIVESESSIONSLOG(
ASESSIONID VARCHAR2(30 ) NOT NULL,
USERID VARCHAR2(30 ),
ACTIVITYSTART TIMESTAMP(6),
ACTIVITYEND TIMESTAMP(6),
ACTIVITY CLOB
)
*/
}
// select all button handle
private Map<Long, Boolean> selectedIds = new HashMap<Long, Boolean>();
// get the list from the JSF page
public Map<Long, Boolean> getSelectedIds() {
return selectedIds;
}
// call this method from the JSF page to delete the selected rows
public String deleteAction() {
// do something with the selected rows
return null;
}
private static Date timestampToDate(java.sql.Timestamp ts) {
Date d = null;
try {
d = new Date(ts.getTime());
} catch (Exception e) {
e.printStackTrace();
}
return d;
}
}
这是JSF页面：
<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:f="http://java.sun.com/jsf/core"
xmlns:ui="http://java.sun.com/jsf/facelets">
<h:head>
<ui:insert name="header">
<ui:include src="header.xhtml"/>
</ui:insert>
</h:head>
<h:body>
<h1><img src="resources/css/images/icon.png" alt="NVIDIA.com" /> History Center</h1>
<!-- layer for black background of the buttons -->
<div id="toolbar" style="margin: 0 auto; width:1180px; height:30px; position:relative; background-color:black">
<!-- Include page Navigation -->
<ui:insert name="Navigation">
<ui:include src="Navigation.xhtml"/>
</ui:insert>
</div>
<div id="greenBand" class="ui-state-default ui-corner-allh" style="position:relative; top:35px; left:0px;">
<h:graphicImage alt="Dashboard" style="position:relative; top:-20px; left:9px;" value="resources/images/logo_sessions.png" />
</div>
<div id="main" style="margin: 0 auto; width:1190px; height:700px; position:absolute; background-color:transparent; top:105px">
<div id="mainpage" style="margin: 0 auto; width:1190px; height:500px; position:absolute; background-color:transparent; top:80px">
<div id="settingsHashMap" style="width:750px; height:400px; position:absolute; background-color:r; top:20px; left:1px">
<h:form id="form">
<!-- The sortable data table -->
<h:dataTable value="#{SessionsController.dataList}" var="item">
<h:column>
<f:facet name="header">
<h:commandLink value="Account Session ID" actionListener="#{SessionsController.sort}">
<f:attribute name="sortField" value="Account Session ID" />
</h:commandLink>
</f:facet>
<h:outputText value="#{item.aSessionID}" />
</h:column>
<h:column>
<f:facet name="header">
<h:commandLink value="User ID" actionListener="#{SessionsController.sort}">
<f:attribute name="sortField" value="User ID" />
</h:commandLink>
</f:facet>
<h:outputText value="#{item.userID}" />
</h:column>
<h:column>
<f:facet name="header">
<h:commandLink value="Activity Start Time" actionListener="#{SessionsController.sort}">
<f:attribute name="sortField" value="Activity Start Time" />
</h:commandLink>
</f:facet>
<h:outputText value="#{item.activityStart}" />
</h:column>
<h:column>
<f:facet name="header">
<h:commandLink value="Activity End Time" actionListener="#{SessionsController.sort}">
<f:attribute name="sortField" value="Activity End Time" />
</h:commandLink>
</f:facet>
<h:outputText value="#{item.activityEnd}" />
</h:column>
<h:column>
<f:facet name="header">
<h:commandLink value="Activity" actionListener="#{SessionsController.sort}">
<f:attribute name="sortField" value="Activity" />
</h:commandLink>
</f:facet>
<h:outputText value="#{item.activity}" />
</h:column>
</h:dataTable>
<!-- The paging buttons -->
<h:commandButton value="first" action="#{SessionsController.pageFirst}"
disabled="#{SessionsController.firstRow == 0}" />
<h:commandButton value="prev" action="#{SessionsController.pagePrevious}"
disabled="#{SessionsController.firstRow == 0}" />
<h:commandButton value="next" action="#{SessionsController.pageNext}"
disabled="#{SessionsController.firstRow + SessionsController.rowsPerPage >= SessionsController.totalRows}" />
<h:commandButton value="last" action="#{SessionsController.pageLast}"
disabled="#{SessionsController.firstRow + SessionsController.rowsPerPage >= SessionsController.totalRows}" />
<h:outputText value="Page #{SessionsController.currentPage} / #{SessionsController.totalPages}" />
<br />
<!-- The paging links -->
<ui:repeat value="#{SessionsController.pages}" var="page">
<h:commandLink value="#{page}" actionListener="#{SessionsController.page}"
rendered="#{page != SessionsController.currentPage}" />
<h:outputText value="#{page}" escape="false"
rendered="#{page == SessionsController.currentPage}" />
</ui:repeat>
<br />
<!-- Set rows per page -->
<h:outputLabel for="rowsPerPage" value="Rows per page" />
<h:inputText id="rowsPerPage" value="#{SessionsController.rowsPerPage}" size="3" maxlength="3" />
<h:commandButton value="Set" action="#{SessionsController.pageFirst}" />
<h:message for="rowsPerPage" errorStyle="color: red;" />
</h:form>
</div>
<div id="settingsdiva" style="width:350px; height:400px; position:absolute; background-color:transparent; top:20px; left:400px">
</div>
<div id="settingsdivb" style="width:350px; height:400px; position:absolute; background-color:transparent; top:20px; left:800px">
</div>
</div>
</div>
</h:body>
</html>
当我尝试显示数据库表中的数据时，JSF表上没有显示任何数据。桌子是空的。这是Glassfish中的错误堆栈：
[#|2012-04-09T16:46:33.241+0300|SEVERE|glassfish3.1.2|javax.enterprise.system.std.com.sun.enterprise.server.logging|_ThreadID=173;_ThreadName=Thread-2;|java.lang.NullPointerException
at com.DX_57.HM_57.Sessions.ActiveSessionsArrayList(Sessions.java:375)
at com.DX_57.HM_57.Sessions.list(Sessions.java:293)
at com.DX_57.HM_57.Sessions.loadDataList(Sessions.java:190)
at com.DX_57.HM_57.Sessions.getDataList(Sessions.java:214)
at sun.reflect.GeneratedMethodAccessor839.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at javax.el.BeanELResolver.getValue(BeanELResolver.java:363)
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.AstValue.getValue(AstValue.java:138)
at com.sun.el.parser.AstValue.getValue(AstValue.java:183)
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 javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:182)
at javax.faces.component.UIData.getValue(UIData.java:731)
at javax.faces.component.UIData.getDataModel(UIData.java:1798)
at javax.faces.component.UIData.setRowIndexWithoutRowStatePreserved(UIData.java:484)
at javax.faces.component.UIData.setRowIndex(UIData.java:473)
at com.sun.faces.renderkit.html_basic.TableRenderer.encodeEnd(TableRenderer.java:191)
at javax.faces.component.UIComponentBase.encodeEnd(UIComponentBase.java:875)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1764)
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:1757)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1760)
at javax.faces.component.UIComponent.encodeAll(UIComponent.java:1760)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:402)
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:131)
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:1542)
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$AdapterCallable.call(ContainerMapper.java:317)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:195)
at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:849)
at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:746)
at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1045)
at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:228)
at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
at java.lang.Thread.run(Thread.java:722)
|#]
我的代码中有一个错误，我找不到。我该如何解决这个问题？
祝福
答案 0 :(得分：5)
这不是特定于JSF的。您在null的第375行有一个Sessions.java引用。去确保不要在null对象上调用方法。在您的特定情况下，这将解决它：
ArrayList<ActiveSessionObj> al = new ArrayList<ActiveSessionObject>();
但下次请尝试阅读异常告诉你的内容。它会告诉您失败的原因以及失败的原因。
答案 1 :(得分：3)
您尚未初始化ArrayList，并且您有一个空指针。
ArrayList<ActiveSessionObj> al = null;
然后你添加它，我认为是抛出错误：
al.add(new ActiveSessionObj(
将其更改为：
ArrayList<ActiveSessionObj> al = new ArrayList<ActiveSessionObj>;
答案 2 :(得分：2)
我认为它就在这里：
private static ArrayList<ActiveSessionObj> ActiveSessionsArrayList(ResultSet rs) throws SQLException {
ArrayList<ActiveSessionObj> al = null;
try {
while (rs.next()) {
可能，就在行号所示的位置。您将al设置为null，然后在语句尝试使用它之后立即执行。