在前后端的交互中，前端通过以下三种方式来与后端进行交互🌟

✅query string

✅form表单

✅JSON字符串

下面我们将书写这三种方式的后端代码并进行讲解

1、Query String

QueryString即在url中写入键值对，一般用doGet方法进行交互

代码如下 

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;@WebServlet("/getParameter")
public class GetParameterServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {String username = req.getParameter("username");String password = req.getParameter("password");System.out.println(username);System.out.println(password);resp.getWriter().write("ok");}
}

用postman验证

 

2、form表单

 form表单一般用doPost方法进行交互

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;@WebServlet("/postParameter")
public class postParameterServlet extends HttpServlet {@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {String username = req.getParameter("username");String password = req.getParameter("password");System.out.println(username);System.out.println(password);resp.getWriter().write("ok");}
}

3、Jason字符串

 （1）关于Jason

Jason是什么

JSON 是存储和交换文本信息的语法，类似 XML。JSON采用完全独立于任何程序语言的文本格式

要在Servlet中实现Jason相关操作，我们使用Jackson解析器

（2）jackson的配置

怎样配置Jackson呢？🧐

在中央仓库搜索Jackson，选中Jackson Databind👆

 点击进去之后，选择2.15.0版本👆

（Jackson2.15.0对应Tomcat8、对应Servlet3.1.0）

进去后，点击复制下面这段代码📃

<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
<dependency><groupId>com.fasterxml.jackson.core</groupId><artifactId>jackson-databind</artifactId><version>2.15.0</version>
</dependency>

粘贴到pom.xml文件中

之后会出现Maven的按钮，点击进行下载 

下载完成后，原本出现的红字报错消失

（3）使用json字符串进行前后端交互

 在配置好json的解析器后，我们书写代码进行前后端交互

import com.fasterxml.jackson.databind.ObjectMapper;import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;//定一个Request类
class Request{public String username;public String password;
}class Response{public Boolean ok;
}@WebServlet("/json")
public class JsonParameterSerlet extends HttpServlet {@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {ObjectMapper mapper = new ObjectMapper();Request request = mapper.readValue(req.getInputStream(),Request.class);//把json字符串映射成Request类的java对象System.out.println("username：" + request.username);System.out.println("password：" + request.password);Response response = new Response();response.ok = true;//将Response类的java对象映射成json字符串String respjson = mapper.writeValueAsString(response);resp.setContentType("applicaton/json;charset=utf8");resp.getWriter().write(respjson);}
}

使用postman进行验证 ​​​​​​​