Spring Boot 註冊 Servlet 的三種方法，真是太有用了！

時間 2019-11-07

標籤 spring boot 註冊 servlet 三種方法真是用了欄目 Spring 简体版

原文原文鏈接

本文棧長教你如何在 Spring Boot 註冊 Servlet、Filter、Listener。java

你所需具有的基礎

更多請在Java技術棧微信公衆號後臺回覆關鍵字：boot。web

1、Spring Boot 註冊

Spring Boot 提供了 ServletRegistrationBean, FilterRegistrationBean, ServletListenerRegistrationBean 三個類分別用來註冊 Servlet, Filter, Listener，下面是 Servlet 的示例代碼。spring

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * @author Java技術棧
 */
public class RegisterServlet extends HttpServlet {

	@Override
	protected void service(HttpServletRequest req, HttpServletResponse resp) throws IOException {
		String name = getServletConfig().getInitParameter("name");
		String sex = getServletConfig().getInitParameter("sex");

		resp.getOutputStream().println("name is " + name);
		resp.getOutputStream().println("sex is " + sex);
	}

}

@Bean
public ServletRegistrationBean registerServlet() {
	ServletRegistrationBean servletRegistrationBean = new ServletRegistrationBean(
			new RegisterServlet(), "/registerServlet");
	servletRegistrationBean.addInitParameter("name", "javastack");
	servletRegistrationBean.addInitParameter("sex", "man");
	return servletRegistrationBean;
}

2、組件掃描註冊

Servlet 3.0 以前，Servlet、Filter、Listener 這些組件都須要在 web.xml 中進行配置，3.0 以後開始再也不須要 web.xml 這個配置文件了，全部的組件均可以經過代碼配置或者註解來達到目的。安全

以下圖所示，截圖自 Servlet 3.1。springboot

Servlet 3.0 開始提供了這 3 個註解來代替。服務器

@WebServlet => 代替 servlet 配置微信

@WebFilter => 代替 filter 配置app

@WebListener => 代替 listener 配置async

配置 Servlet 示例

import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * @author Java技術棧
 */
@WebServlet(name = "javaServlet", urlPatterns = "/javastack.cn", asyncSupported = true,
		initParams = {
		@WebInitParam(name = "name", value = "javastack"),
		@WebInitParam(name = "sex", value = "man") })
public class JavaServlet extends HttpServlet {

	@Override
	protected void service(HttpServletRequest req, HttpServletResponse resp) throws IOException {
		String name = getServletConfig().getInitParameter("name");
		String sex = getServletConfig().getInitParameter("sex");

		resp.getOutputStream().println("name is " + name);
		resp.getOutputStream().println("sex is " + sex);
	}

}

配置 Filter 示例

/**
 * @author Java技術棧
 */
@WebFilter(filterName = "javaFilter", urlPatterns = "/*", initParams = {
		@WebInitParam(name = "name", value = "javastack"),
		@WebInitParam(name = "code", value = "123456") })
public class JavaFilter implements Filter {

	@Override
	public void init(FilterConfig filterConfig) throws ServletException {
		System.out.println("java filter init.");
		String name = filterConfig.getInitParameter("name");
		String code = filterConfig.getInitParameter("code");
		System.out.println("name is " + name);
		System.out.println("code is " + code);
	}

	@Override
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
			throws IOException, ServletException {
		System.out.println("java filter processing.");
		chain.doFilter(request, response);
	}

	@Override
	public void destroy() {
		System.out.println("java filter destroy.");
	}

}

Listener 配置方式相似，上面的示例代碼一看就懂，這裏再也不詳述。ide

須要注意的是，爲了安全考慮，內嵌服務器不會直接執行 Servlet 3.0 裏面的 javax.servlet.ServletContainerInitializer 接口，或者 Spring 中的 org.springframework.web.WebApplicationInitializer 接口，不然會致使終止 Spring Boot 應用。

因此，若是使用的是 Spring Boot 內嵌服務器，須要在配置類上面添加額外的 @ServletComponentScan 註解來開啓 Servlet 組件掃描功能，若是使用的是獨立的服務器，則不須要添加，會使用服務器內部的自動發現機制。

3、動態註冊

若是你想在 Spring Boot 中完成 Servlet、Filter、Listener 的初始化操做，你須要在 Spring 中實現下面這個接口，並註冊爲一個 bean。

org.springframework.boot.web.servlet.ServletContextInitializer

ServletContext 提供了幾個動態註冊的方法，以下所示。

如下爲動態添加 Servlet 示例代碼。

import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * @author Java技術棧
 */
@WebServlet(name = "javaServlet", urlPatterns = "/javastack.cn", asyncSupported = true,
		initParams = {
		@WebInitParam(name = "name", value = "javastack"),
		@WebInitParam(name = "sex", value = "man") })
public class JavaServlet extends HttpServlet {

	@Override
	protected void service(HttpServletRequest req, HttpServletResponse resp) throws IOException {
		String name = getServletConfig().getInitParameter("name");
		String sex = getServletConfig().getInitParameter("sex");

		resp.getOutputStream().println("name is " + name);
		resp.getOutputStream().println("sex is " + sex);
	}

}

import cn.javastack.springbootbestpractice.servlet.InitServlet;
import org.springframework.boot.web.servlet.ServletContextInitializer;
import org.springframework.stereotype.Component;

import javax.servlet.ServletContext;
import javax.servlet.ServletRegistration;

/**
 * @author Java技術棧
 */
@Component
public class ServletConfig implements ServletContextInitializer {

	@Override
	public void onStartup(ServletContext servletContext) {
		ServletRegistration initServlet = servletContext
				.addServlet("initServlet", InitServlet.class);
		initServlet.addMapping("/initServlet");
		initServlet.setInitParameter("name", "javastack");
		initServlet.setInitParameter("sex", "man");
	}

}