用Servlet實現Restful API簡單範例。
最近碰到沒用框架單用Servlet硬幹Restful API的老舊專案，已經好久沒碰Servet這Java Web底層的東西，所以試驗一下。
範例環境：
- Eclipse
- Java 1.8
- Servlet 4.0
- Maven
首先使用maven-archetype-webapp建立一個Maven Web專案servlet-demo。context path預設為專案名稱。
在WEB-INF/web.xml設定DemoServlet的<servlet-mapping>，將context path下/demo開頭的請求都導向給DemoServlet處理。
web.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE xml>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
version="4.0">
<display-name>Servlet Web Application</display-name>
<servlet>
<servlet-name>DemoServlet</servlet-name>
<servlet-class>com.abc.demo.DemoServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>DemoServlet</servlet-name>
<url-pattern>/demo/*</url-pattern>
</servlet-mapping>
</web-app>
建立DemoServlet繼承HttpServlet，負責處理請求的Restful API。
DemoServlet
package com.abc.demo;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.lang3.StringUtils;
import com.abc.demo.dto.ApiResposne;
import com.abc.demo.dto.EmployeeDto;
import com.fasterxml.jackson.databind.ObjectMapper;
public class DemoServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
public DemoServlet() {
super();
}
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String pathInfo = request.getPathInfo();
if (StringUtils.isEmpty(pathInfo)) {
response.sendError(HttpServletResponse.SC_NOT_FOUND);
return;
}
ObjectMapper objectMapper = new ObjectMapper();
String jsonString = "";
PrintWriter writer = response.getWriter();
if ("/employee".equalsIgnoreCase(pathInfo)) {
EmployeeDto employeeDto = new EmployeeDto(1L, "john", "john@abc.com", 28);
ApiResposne apiResposne = new ApiResposne("success", employeeDto);
jsonString = objectMapper.writeValueAsString(apiResposne);
writer.write(jsonString);
return;
}
response.sendError(HttpServletResponse.SC_NOT_FOUND);
}
}
DemoServlet.doGet()程式中用到的值類別。
EmployeeDto
package com.abc.demo.dto;
public class EmployeeDto {
private Long id;
private String name;
private String email;
private Integer age;
public EmployeeDto(Long id, String name, String email, Integer age) {
this.id = id;
this.name = name;
this.email = email;
this.age = age;
}
// getters and setters
}
ApiResposne
package com.abc.demo.dto;
public class ApiResposne {
private String message;
private Object data;
public ApiResposne(String message, Object data) {
this.message = message;
this.data = data;
}
// getters and setters
}
以上邏輯建立的API為GET|/demo/employee，doGet()是用來處理HTTP GET請求的方法。若url輸入正確會把EmployeeDto轉為json字串回應出去。
設定完以上後啟動專案。
使用Postman測試，在url欄位使用GET，位址輸入http://localhost:8080/servlet-demo/demo/employee送出請求。
回應結果如下。
{"message":"success","data":{"id":1,"name":"john","email":"john@abc.com","age":28}}
參考github。
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