JavaWeb学习-Servlet系列-22-HttpServletRequest获取表单内容并封装成高级对象

旧城等待， 2022-01-31 03:25 151阅读 0赞

这篇还是来学习HttpServletRequest如何获取表单内容的相关方法，本篇重点学习getParameterMap()这个方法，就是得到表单里全部键值对，返回一个map对象。我们实际开发中，得到表单数据肯定不是为了打印到控制台，而是存入到数据库。在存入数据库之前，我们拿到零散的数据去操作效率很低，一般我们都要封装成高级对象（Java Bean），然后通过JDBC存入数据库。本篇具体来学习如何得到表单数据并封装成高级对象的过程。

1.先写一个高级对象User.java

package com.anthony.entity;
    
    import java.util.Arrays;
    
    public class User {
    	private String userName;
    	private String pwd;
    	private String gender;
    	private String[] hobby;
    	private String city;
    	public String getUserName() {
    		return userName;
    	}
    	public void setUserName(String userName) {
    		this.userName = userName;
    	}
    	public String getPwd() {
    		return pwd;
    	}
    	public void setPwd(String pwd) {
    		this.pwd = pwd;
    	}
    	public String getGender() {
    		return gender;
    	}
    	public void setGender(String gender) {
    		this.gender = gender;
    	}
    	public String[] getHobby() {
    		return hobby;
    	}
    	public void setHobby(String[] hobby) {
    		this.hobby = hobby;
    	}
    	public String getCity() {
    		return city;
    	}
    	public void setCity(String city) {
    		this.city = city;
    	}
    	
    	@Override
    	public String toString() {
    		return "User [userName=" + userName + ", pwd=" + pwd + ", gender=" + gender + ", hobby="
    				+ Arrays.toString(hobby) + ", city=" + city + "]";
    	}
    	
    	
    
    }

这些字段和register.html中name一致，具体register.html内容请看前面文章。

2.ServletDemo.java内容

package com.anthony.servlet;
    
    import java.beans.IntrospectionException;
    import java.beans.PropertyDescriptor;
    import java.io.IOException;
    import java.lang.reflect.Method;
    import java.util.Enumeration;
    import java.util.Map;
    import java.util.Map.Entry;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    import com.anthony.entity.User;
    
    
    public class ServletDemo4 extends HttpServlet {
    
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		req.setCharacterEncoding("UTF-8");
    		try {
    			User u = new User();
    			System.out.println("封装数据之前的用户数据：" + u);
    			//获取表单里数据，返回是一个map
    			Map<String, String[]> map = req.getParameterMap();
    			
    			for (Entry<String, String[]> m : map.entrySet()) {
    				String name = m.getKey();
    				String[] value = m.getValue();
    				
    				//创建一个属性描述器
    				PropertyDescriptor dp = new PropertyDescriptor(name, User.class);
    				Method setter = dp.getWriteMethod();
    				
    				if(value.length == 1) {
    					setter.invoke(u, value[0]);
    				}else {
    					setter.invoke(u, (Object)value);
    				}
    			}
    			System.out.println("封装数据之后的用户数据：" + u);
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    	}
    
    
    	private void test(HttpServletRequest req) {
    		//获取表单中全部name的值
    		Enumeration<String> names = req.getParameterNames();
    		while(names.hasMoreElements()) {
    			String name = names.nextElement();
    			
    			//考虑到hobby下有多个值
    			String[] values = req.getParameterValues(name);
    			for (int i = 0; values != null && i < values.length; i++) {
    				System.out.println(name +"\t"+ values[i]);
    			}
    		}
    	}
    
    
    	@Override
    	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		doGet(req, resp);
    	}
    	
    }

重点理解上面代码描述器PropertyDescriptor的使用，通过反射可以找到User.class，然后PropertyDescriptor对象有获取高级对象类中setter和getter方法，上面我们只用了得到setter方法，然后遍历map集合，封装成User对象。

测试运行效果

信息: Server startup in 522 ms
    封装数据之前的用户数据：User [userName=null, pwd=null, gender=null, hobby=null, city=null]
    封装数据之后的用户数据：User [userName=AnthonyLiu, pwd=123abc, gender=男, hobby=[唱歌, 编码], city=BJ]