Spring 教程：Servlet 过滤器

【注】本文译自： [https://www.tutorialspoint.com/spring_boot/spring_boot_servlet_filter.htm](https://www.tutorialspoint.com/spring_boot/spring_boot_servlet_filter.htm)


过滤器是一种拦截应用中 HTTP 请求和响应的对象，使用过滤器，你可以执行以下两种情形下的两种操作：

下面的示例代码是以 @Component 注解的类来实现 Servlet 过滤器：

public class SimpleFilter implements Filter {   @Override   public void destroy() {}   @Override   public void doFilter      (ServletRequest request, ServletResponse response, FilterChain filterchain)       throws IOException, ServletException {}   @Override   public void init(FilterConfig filterconfig) throws ServletException {}}

       下面的示例代码展示了在发送请求到控制器之前，从 ServletRequest 对象读取远程主机和地址：

在 doFilter() 方法中，我们加了 System.out.println 语句打印远程主机和地址：

package com.tutorialspoint.demo;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import org.springframework.stereotype.Component;@Componentpublic class SimpleFilter implements Filter {   @Override   public void destroy() {}   @Override   public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterchain)       throws IOException, ServletException {            System.out.println("Remote Host:"+request.getRemoteHost());      System.out.println("Remote Address:"+request.getRemoteAddr());      filterchain.doFilter(request, response);   }   @Override   public void init(FilterConfig filterconfig) throws ServletException {}}

       在 Spring Boot 主应用类文件中，我们加了简单 REST 端点返回 “Hello World” 字串：

package com.tutorialspoint.demo;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController;@SpringBootApplication@RestControllerpublic class DemoApplication {   public static void main(String[] args) {      SpringApplication.run(DemoApplication.class, args);   }   @RequestMapping(value = "/")   public String hello() {      return "Hello World";   }}

       Maven build – pom.xml 代码如下：

<?xml version = "1.0" encoding = "UTF-8"?><project xmlns = "http://maven.apache.org/POM/4.0.0" xmlns:xsi = "   http://www.w3.org/2001/XMLSchema-instance"   xsi:schemaLocation = "http://maven.apache.org/POM/4.0.0    http://maven.apache.org/xsd/maven-4.0.0.xsd">      <modelVersion>4.0.0</modelVersion>   <groupId>com.tutorialspoint</groupId>   <artifactId>demo</artifactId>   <version>0.0.1-SNAPSHOT</version>   <packaging>jar</packaging>   <name>demo</name>   <description>Demo project for Spring Boot</description>   <parent>      <groupId>org.springframework.boot</groupId>      <artifactId>spring-boot-starter-parent</artifactId>      <version>1.5.8.RELEASE</version>      <relativePath/>    </parent>   <properties>      <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>      <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>      <java.version>1.8</java.version>   </properties>   <dependencies>      <dependency>         <groupId>org.springframework.boot</groupId>         <artifactId>spring-boot-starter-web</artifactId>      </dependency>      <dependency>         <groupId>org.springframework.boot</groupId>         <artifactId>spring-boot-starter-test</artifactId>         <scope>test</scope>      </dependency>   </dependencies>   <build>      <plugins>         <plugin>            <groupId>org.springframework.boot</groupId>            <artifactId>spring-boot-maven-plugin</artifactId>         </plugin>      </plugins>   </build></project>

       Gradle Build – build.gradle 代码如下：

buildscript {   ext {      springBootVersion = '1.5.8.RELEASE'   }   repositories {      mavenCentral()   }   dependencies {      classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")   }}apply plugin: 'java'apply plugin: 'eclipse'apply plugin: 'org.springframework.boot'group = 'com.tutorialspoint'version = '0.0.1-SNAPSHOT'sourceCompatibility = 1.8repositories {   mavenCentral()}dependencies {   compile('org.springframework.boot:spring-boot-starter-web')   testCompile('org.springframework.boot:spring-boot-starter-test')}

       你可以使用以下 Maven 或 Gradle 命令来创建可执行 JAR 文件，运行 Spring Boot 应用：

Maven 命令如下：

mvn clean install

       在 BUILD SUCCESS 之后，你可以在 target 目录下找到 JAR 文件。

Gradle 命令如下：

gradle clean build

       在 BUILD SUCCESSFUL 之后，你可以在 build/libs 目录下找到 JAR 文件。

现在，使用下面的命令运行 JAR 文件：

java –jar

你可以看到应用已经在 Tomcat 端口号 8080 启动了。

现在单击 URL [http://localhost:8080/](http://localhost:8080/) 可以看到输出了 Hello World。看起来应当是下面的样子：

https://p1-tt.byteimg.com/origin/pgc-image/94236e83cc174ab59ea990e4f1311e2b

然后你可以看到如下所示的控制台日志：