Struts2 简单的增删改查
1：主页面
<a href="emp-list">emp-list</a> <br>
然后到struts.xml文件中找到对应的emp-list
<action name="emp-list" class="com.emp.app.EmployeeAction" method="List">
<result name="list">/pages/emp-list.jsp</result>
</action>
然后在Action处理业务层处理。class="com.emp.app.EmployeeAction"
package com.emp.app; import java.util.Map; import org.apache.struts2.interceptor.RequestAware; public class EmployeeAction implements RequestAware{ private Dao dao = new Dao(); private Employee employee;
private Map<String, Object> request;
public void setRequest(Map<String, Object> arg0) { this.request = arg0; } public String List(){ System.out.println(dao.getEmployees()); request.put("emps", dao.getEmployees()); System.out.println(request.size()); return "list"; }
private Integer employeeId;
public void setEmployeeId(Integer employeeId) {
this.employeeId = employeeId;
}
public String delete(){
dao.deleteEmployees(employeeId);
return "success";
} }
到DAO层处理数据：
package com.emp.app; import java.util.ArrayList; import java.util.LinkedHashMap; import java.util.List; import java.util.Map; import com.opensymphony.xwork2.ActionContext; import com.opensymphony.xwork2.util.ValueStack; public class Dao { ValueStack vs=ActionContext.getContext().getValueStack(); private static Map<Integer, Employee> emps = new LinkedHashMap<Integer, Employee>(); static{ emps.put(1001, new Employee(1001, "AA", "aa", "aa@atguigu.com")); emps.put(1002, new Employee(1002, "BB", "bb", "bb@atguigu.com")); emps.put(1003, new Employee(1003, "CC", "cc", "cc@atguigu.com")); emps.put(1004, new Employee(1004, "DD", "dd", "dd@atguigu.com")); emps.put(1005, new Employee(1005, "EE", "ee", "ee@atguigu.com")); } public List<Employee> getEmployees(){ return new ArrayList<Employee>(emps.values()); } public Employee deleteEmployees(Integer empId){ return emps.remove(empId); } }
处理完后 result到对应的页面展示数据。
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@taglib prefix="s" uri="/struts-tags" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<h1>显示全部</h1>
</head>
<body>
<table cellpadding="10" cellspacing="0" border="1">
<thead>
<tr>
<td>ID</td>
<td>FirstName</td>
<td>LastName</td>
<td>Email</td>
<td>Edit</td>
<td>Delete</td>
</tr>
</thead>
<tbody>
<s:iterator value="#request.emps">
<tr>
<td>${employeeId }</td>
<td>${firstName }</td>
<td>${lastName }</td>
<td>${email }</td>
<td><a href="emp-edit?employeeId=${employeeId }">Edit</a></td>
<td><a href="emp-delete?employeeId=${employeeId }">Delete</a></td>
</tr>
</s:iterator>
</tbody>
</table>
<s:debug></s:debug>
</body>
</html>
二：保存
1）：struts2的运行流程。
拦截器中有个parameters拦截器。它的用处是：把表单字段映射到ValueStack栈的栈顶对象的各个属性中。如果某个字段在模型里没有匹配的属性。Param拦截器将尝试把字段压入到ValueStack栈中的下一个对象。
把表单的值赋给栈顶对象的属性。此时栈顶对象是Action。
拦截器的顺序是从第一个到最后一个依次进行。
2）：ModelDriven拦截器：
作用：将ModelDriven拦截器接口的getModel()方法返回的对象置于栈顶。
1. Action 实现 ModelDriven 接口后的运行流程
1). 先会执行 ModelDrivenInterceptor 的 intercept 方法.
public String intercept(ActionInvocation invocation) throws Exception {
//获取 Action 对象: EmployeeAction 对象, 此时该 Action 已经实现了 ModelDriven 接口
//public class EmployeeAction implements RequestAware, ModelDriven<Employee>
Object action = invocation.getAction();
//判断 action 是否是 ModelDriven 的实例
if (action instanceof ModelDriven) {
//强制转换为 ModelDriven 类型
ModelDriven modelDriven = (ModelDriven) action;
//获取值栈
ValueStack stack = invocation.getStack();
//调用 ModelDriven 接口的 getModel() 方法
//即调用 EmployeeAction 的 getModel() 方法
/*
public Employee getModel() {
employee = new Employee();
return employee;
}
*/
Object model = modelDriven.getModel();
if (model != null) {
//把 getModel() 方法的返回值压入到值栈的栈顶. 实际压入的是 EmployeeAction 的 employee 成员变量
stack.push(model);
}
if (refreshModelBeforeResult) {
invocation.addPreResultListener(new RefreshModelBeforeResult(modelDriven, model));
}
}
return invocation.invoke();
}
2). 执行 ParametersInterceptor 的 intercept 方法: 把请求参数的值赋给栈顶对象对应的属性. 若栈顶对象没有对应的属性, 则查询
值栈中下一个对象对应的属性...
3). 注意: getModel 方法不能提供以下实现. 的确会返回一个 Employee 对象到值栈的栈顶. 但当前 Action
的 employee 成员变量却是 null.
public Employee getModel() {
return new Employee();
}
代码实现：
package com.emp.app; import java.util.Map; import org.apache.struts2.interceptor.RequestAware; import com.opensymphony.xwork2.ModelDriven; public class EmployeeAction implements RequestAware,ModelDriven<Employee>{ private Dao dao = new Dao(); private Employee employee; public Employee getModel() { employee=new Employee(); return employee; } public String save(){ dao.save(employee); return "success"; } }
DAO层：
public void save(Employee employee){ long time=System.currentTimeMillis(); employee.setEmployeeId((int)time); emps.put(employee.getEmployeeId(), employee); }
页面：emp-save.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@taglib prefix="s" uri="/struts-tags" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<h1>添加一个</h1>
</head>
<body>
<s:form action="emp-save">
<s:textfield name="firstName" label="FirstName"></s:textfield>
<s:textfield name="lastName" label="LastName"></s:textfield>
<s:textfield name="email" label="Email"></s:textfield>
<s:submit></s:submit>
</s:form>
<s:debug></s:debug>
</body>
</html>
四：修改
页面：
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<s:debug></s:debug>
<br>
<br>
<s:form action="emp-update">
<s:hidden name="employeeId"></s:hidden>
<s:textfield name="firstName" label="FirstName"></s:textfield>
<s:textfield name="lastName" label="LastName"></s:textfield>
<s:textfield name="email" label="Email"></s:textfield>
<s:submit></s:submit>
</s:form>
</body>
</html>
DAO层：
public Employee get(Integer empId){ System.out.println(empId+"aaa"); return emps.get(empId); } public void update(Employee emp){ emps.put(emp.getEmployeeId(), emp); }
先得到ID，然后修改Employee对象
package com.emp.app; import java.util.Map; import org.apache.struts2.interceptor.RequestAware; import com.opensymphony.xwork2.ModelDriven; public class EmployeeAction implements RequestAware,ModelDriven<Employee>{ private Dao dao = new Dao(); private Employee employee; public Employee getModel() {
/*判断是创建还是修改。若是创建。employee=new Employee();
修改：employee=dao.get(employeeId);
判断标准就是有没有employeeId这个参数。
若通过employeeId来判断。需要在modelDriven拦截器先执行一个params拦截器。因为params拦截器是把表单的值赋予栈顶的对象。
需要在struts.xml中配置默认的 paramsPrepareParamsStack拦截器
<default-interceptor-ref name="paramsPrepareParamsStack"></default-interceptor-ref>
*/
目的就是从栈顶中得到employee对象。然后修改的时候回显到emp-edit.jsp页面。 if(employeeId==null) employee=new Employee(); else employee=dao.get(employeeId); return employee; } private Integer employeeId; public void setEmployeeId(Integer employeeId) { this.employeeId = employeeId; } public String edit(){ return "edit"; } public String update(){ dao.update(employee); return "success"; } }
5）：存在的问题: getModel 方法 public Employee getModel() { if(employeeId == null) employee = new Employee(); else employee = dao.get(employeeId); return employee; } I. 在执行删除的时候, employeeId 不为 null, 但 getModel 方法却从数据库加载了一个对象. 不该加载! II. 指向查询全部信息时, 也 new Employee() 对象. 浪费! . 解决方案: 使用 PrepareInterceptor 和 Preparable 接口. 7). 关于 PrepareInterceptor [分析后得到的结论] 若 Action 实现了 Preparable 接口, 则 Struts 将尝试执行 prepare[ActionMethodName] 方法, 若 prepare[ActionMethodName] 不存在, 则将尝试执行 prepareDo[ActionMethodName] 方法. 若都不存在, 就都不执行. 若 PrepareInterceptor 的 alwaysInvokePrepare 属性为 false, 则 Struts2 将不会调用实现了 Preparable 接口的 Action 的 prepare() 方法 [能解决 5) 的问题的方案] 可以为每一个 ActionMethod 准备 prepare[ActionMethdName] 方法, 而抛弃掉原来的 prepare() 方法 将 PrepareInterceptor 的 alwaysInvokePrepare 属性置为 false, 以避免 Struts2 框架再调用 prepare() 方法. 如何在配置文件中为拦截器栈的属性赋值: 参看 /struts-2.3.15.3/docs/WW/docs/interceptors.html <interceptors> <interceptor-stack name="parentStack"> <interceptor-ref name="defaultStack"> <param name="params.excludeParams">token</param> </interceptor-ref> </interceptor-stack> </interceptors> <default-interceptor-ref name="parentStack"/> ----------------------------------源代码解析--------------------------------- public String doIntercept(ActionInvocation invocation) throws Exception { //获取 Action 实例 Object action = invocation.getAction(); //判断 Action 是否实现了 Preparable 接口 if (action instanceof Preparable) { try { String[] prefixes; //根据当前拦截器的 firstCallPrepareDo(默认为 false) 属性确定 prefixes if (firstCallPrepareDo) { prefixes = new String[] {ALT_PREPARE_PREFIX, PREPARE_PREFIX}; } else { prefixes = new String[] {PREPARE_PREFIX, ALT_PREPARE_PREFIX}; } //若为 false, 则 prefixes: prepare, prepareDo //调用前缀方法. PrefixMethodInvocationUtil.invokePrefixMethod(invocation, prefixes); } catch (InvocationTargetException e) { Throwable cause = e.getCause(); if (cause instanceof Exception) { throw (Exception) cause; } else if(cause instanceof Error) { throw (Error) cause; } else { throw e; } } //根据当前拦截器的 alwaysInvokePrepare(默认是 true) 决定是否调用 Action 的 prepare 方法 if (alwaysInvokePrepare) { ((Preparable) action).prepare(); } } return invocation.invoke(); } PrefixMethodInvocationUtil.invokePrefixMethod(invocation, prefixes) 方法: public static void invokePrefixMethod(ActionInvocation actionInvocation, String[] prefixes) throws InvocationTargetException, IllegalAccessException { //获取 Action 实例 Object action = actionInvocation.getAction(); //获取要调用的 Action 方法的名字(update) String methodName = actionInvocation.getProxy().getMethod(); if (methodName == null) { // if null returns (possible according to the docs), use the default execute methodName = DEFAULT_INVOCATION_METHODNAME; } //获取前缀方法 Method method = getPrefixedMethod(prefixes, methodName, action); //若方法不为 null, 则通过反射调用前缀方法 if (method != null) { method.invoke(action, new Object[0]); } } PrefixMethodInvocationUtil.getPrefixedMethod 方法: public static Method getPrefixedMethod(String[] prefixes, String methodName, Object action) { assert(prefixes != null); //把方法的首字母变为大写 String capitalizedMethodName = capitalizeMethodName(methodName); //遍历前缀数组 for (String prefixe : prefixes) { //通过拼接的方式, 得到前缀方法名: 第一次 prepareUpdate, 第二次 prepareDoUpdate String prefixedMethodName = prefixe + capitalizedMethodName; try { //利用反射获从 action 中获取对应的方法, 若有直接返回. 并结束循环. return action.getClass().getMethod(prefixedMethodName, EMPTY_CLASS_ARRAY); } catch (NoSuchMethodException e) { // hmm -- OK, try next prefix if (LOG.isDebugEnabled()) { LOG.debug("cannot find method [#0] in action [#1]", prefixedMethodName, action.toString()); } } } return null; }
使用：ModelDriven<Employee>, Preparable
package com.atguigu.struts2.app; import java.util.Map; import org.apache.struts2.interceptor.RequestAware; import com.opensymphony.xwork2.ModelDriven; import com.opensymphony.xwork2.Preparable; public class EmployeeAction implements RequestAware, ModelDriven<Employee>, Preparable{ private Dao dao = new Dao(); private Employee employee; public String update(){ dao.update(employee); return "success"; } public void prepareUpdate(){ employee = new Employee(); } public String edit(){ return "edit"; } public void prepareEdit(){ employee = dao.get(employeeId); } public String save(){ dao.save(employee); return "success"; } public void prepareSave(){ employee = new Employee(); } public String delete(){ dao.delete(employeeId); return "success"; } public String list(){ request.put("emps", dao.getEmployees()); return "list"; } private Map<String, Object> request; @Override public void setRequest(Map<String, Object> arg0) { this.request = arg0; } private Integer employeeId; public void setEmployeeId(Integer employeeId) { this.employeeId = employeeId; } @Override public Employee getModel() { return employee; } @Override public void prepare() throws Exception { System.out.println("prepare..."); } }
在struts.xml中修改 PrepareInterceptor 拦截器的 alwaysInvokePrepare 属性值为 false
<!-- 配置使用 paramsPrepareParamsStack 作为默认的拦截器栈 -->
<!-- 修改 PrepareInterceptor 拦截器的 alwaysInvokePrepare 属性值为 false -->
<interceptors>
<interceptor-stack name="atguigustack">
<interceptor-ref name="paramsPrepareParamsStack">
<param name="prepare.alwaysInvokePrepare">false</param>
</interceptor-ref>
</interceptor-stack>
</interceptors>
<default-interceptor-ref name="atguigustack"/>
