【发布时间】：2011-06-02 11:54:51
【问题描述】：
我正在解决如何在不使用会话范围托管 bean 的情况下将值从一个页面传递到另一个页面。对于大多数托管 bean，我希望只有 Request 范围。
我创建了一个非常非常简单的计算器示例，该示例传递 Result 对象，该对象是从第 5 阶段对请求 bean (CalculatorRequestBean) 的操作产生的，作为在下一阶段生命周期中初始化的请求 bean 的新实例的初始化值。
事实上——在生产环境中，我们需要传递更复杂的数据对象，它不像下面定义的 Result 那样原始。
您对这种考虑两种可能性的解决方案有何看法 - 我们保持相同的观点，或者我们导航到新的观点。但在这两种情况下，我都可以使用视图范围的托管 bean 获取先前存储的值。
计算器页面：
<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:h="http://java.sun.com/jsf/html">
<h:head>
<title>Calculator</title>
</h:head>
<h:body>
<h:form>
<h:panelGrid columns="2">
<h:outputText value="Value to use:"/>
<h:inputText value="#{calculatorBeanRequest.valueToAdd}"/>
<h:outputText value="Navigate to new view:"/>
<h:selectBooleanCheckbox value="#{calculatorBeanRequest.navigateToNewView}"/>
<h:commandButton value="Add" action="#{calculatorBeanRequest.add}"/>
<h:commandButton value="Subtract" action="#{calculatorBeanRequest.subtract}"/>
<h:outputText value="Result:"/>
<h:outputText value="#{calculatorBeanRequest.result.value}"/>
<h:commandButton value="Calculator2" action="calculator2"/>
<h:outputText value="DUMMY" rendered="#{resultBeanView.dummy}"/>
</h:panelGrid>
</h:form>
</h:body>
具有乘除运算的Calculator2页面：
<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:h="http://java.sun.com/jsf/html">
<h:head>
<title>Calculator 2</title>
</h:head>
<h:body>
<h:form>
<h:panelGrid columns="2">
<h:outputText value="Value to use:"/>
<h:inputText value="#{calculatorBeanRequest2.valueToAdd}"/>
<h:outputText value="Navigate to new view:"/>
<h:selectBooleanCheckbox value="#{calculatorBeanRequest2.navigateToNewView}"/>
<h:commandButton value="Multiply" action="#{calculatorBeanRequest2.multiply}"/>
<h:commandButton value="Divide" action="#{calculatorBeanRequest2.divide}"/>
<h:outputText value="Result:"/>
<h:outputText value="#{calculatorBeanRequest2.result.value}"/>
<h:commandButton value="Calculator" action="calculator"/>
<h:outputText value="DUMMY" rendered="#{resultBeanView.dummy}"/>
</h:panelGrid>
</h:form>
</h:body>
</html>
要通过生命周期的对象：
package cz.test.calculator;
import java.io.Serializable;
/**
* Data object passed among pages.
* Lets imagine it holds something much more complicated than primitive int
*/
public class Result implements Serializable {
private int value;
public void setValue(int value) {
this.value = value;
}
public int getValue() {
return value;
}
}
请求在视图“calculator.xhtml”上使用的范围内的托管 bean，带有加减操作
package cz.test.calculator;
import javax.annotation.PostConstruct;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.ManagedProperty;
import javax.faces.bean.RequestScoped;
@ManagedBean
@RequestScoped
public class CalculatorBeanRequest {
@ManagedProperty(value="#{resultBeanView}")
ResultBeanView resultBeanView;
private Result result;
private int valueToAdd;
/**
* Should perform navigation to
*/
private boolean navigateToNewView;
/** Creates a new instance of CalculatorBeanRequest */
public CalculatorBeanRequest() {
}
@PostConstruct
public void init() {
// Remember already saved result from view scoped bean
result = resultBeanView.getResult();
}
// Dependency injections
public void setResultBeanView(ResultBeanView resultBeanView) {
this.resultBeanView = resultBeanView;
}
public ResultBeanView getResultBeanView() {
return resultBeanView;
}
// Getters, setter
public void setValueToAdd(int valueToAdd) {
this.valueToAdd = valueToAdd;
}
public int getValueToAdd() {
return valueToAdd;
}
public boolean isNavigateToNewView() {
return navigateToNewView;
}
public void setNavigateToNewView(boolean navigateToNewView) {
this.navigateToNewView = navigateToNewView;
}
public Result getResult() {
return result;
}
// Actions
public String add() {
result.setValue(result.getValue() + valueToAdd);
return isNavigateToNewView() ? "calculator" : null;
}
public String subtract() {
result.setValue(result.getValue() - valueToAdd);
return isNavigateToNewView() ? "calculator" : null;
}
}
在视图“calculator2.xhtml”上使用请求范围的托管 bean，并执行除法运算：
package cz.test.calculator;
import javax.annotation.PostConstruct;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.ManagedProperty;
import javax.faces.bean.RequestScoped;
@ManagedBean
@RequestScoped
public class CalculatorBeanRequest2 {
@ManagedProperty(value="#{resultBeanView}")
ResultBeanView resultBeanView;
private Result result;
private int valueToUse;
/**
* Should perform navigation to
*/
private boolean navigateToNewView;
/** Creates a new instance of CalculatorBeanRequest2 */
public CalculatorBeanRequest2() {
}
@PostConstruct
public void init() {
result = resultBeanView.getResult();
}
// Dependency injections
public void setResultBeanView(ResultBeanView resultBeanView) {
this.resultBeanView = resultBeanView;
}
public ResultBeanView getResultBeanView() {
return resultBeanView;
}
// Getters, setter
public void setValueToAdd(int valueToAdd) {
this.valueToUse = valueToAdd;
}
public int getValueToAdd() {
return valueToUse;
}
public boolean isNavigateToNewView() {
return navigateToNewView;
}
public void setNavigateToNewView(boolean navigateToNewView) {
this.navigateToNewView = navigateToNewView;
}
public Result getResult() {
return result;
}
// Actions
public String multiply() {
result.setValue(result.getValue() * valueToUse);
return isNavigateToNewView() ? "calculator2" : null;
}
public String divide() {
result.setValue(result.getValue() / valueToUse);
return isNavigateToNewView() ? "calculator2" : null;
}
}
最后查看作用域托管 bean 以将 Result 变量传递到新页面：
package cz.test.calculator;
import java.io.Serializable;
import javax.annotation.PostConstruct;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.ViewScoped;
import javax.faces.context.FacesContext;
@ManagedBean
@ViewScoped
public class ResultBeanView implements Serializable {
private Result result = new Result();
/** Creates a new instance of ResultBeanView */
public ResultBeanView() {
}
@PostConstruct
public void init() {
// Try to find request bean ManagedBeanRequest and reset result value
CalculatorBeanRequest calculatorBeanRequest = (CalculatorBeanRequest)FacesContext.getCurrentInstance().getExternalContext().getRequestMap().get("calculatorBeanRequest");
if(calculatorBeanRequest != null) {
setResult(calculatorBeanRequest.getResult());
}
CalculatorBeanRequest2 calculatorBeanRequest2 = (CalculatorBeanRequest2)FacesContext.getCurrentInstance().getExternalContext().getRequestMap().get("calculatorBeanRequest2");
if(calculatorBeanRequest2 != null) {
setResult(calculatorBeanRequest2.getResult());
}
}
/** No need to have public modifier as not used on view
* but only in managed bean within the same package
*/
void setResult(Result result) {
this.result = result;
}
/** No need to have public modifier as not used on view
* but only in managed bean within the same package
*/
Result getResult() {
return result;
}
/**
* To be called on page to instantiate ResultBeanView in Render view phase
*/
public boolean isDummy() {
return false;
}
}
【问题讨论】：