Servlet Filter

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2023-12-01

过滤器是用于拦截应用程序的HTTP请求和响应的对象。通过使用过滤器，我们可以在两个实例上执行两个操作 -

在将请求发送到控制器之前
在向客户发送响应之前。

以下代码显示了带有@Component批注的Servlet Filter实现类的示例代码。

@Component
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 {}
}

以下示例显示了在将请求发送到控制器之前从ServletRequest对象读取远程主机和远程地址的代码。

在doFilter（）方法中，我们添加了System.out.println语句来打印远程主机和远程地址。

package cn.xnip.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;
@Component
public 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主应用程序类文件中，我们添加了返回“Hello World”字符串的简单REST端点。

package cn.xnip.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
@RestController
public 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的代码如下 -

<?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>cn.xnip</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的代码如下 -

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 = 'cn.xnip'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = 1.8
repositories {
   mavenCentral()
}
dependencies {
   compile('org.springframework.boot:spring-boot-starter-web')
   testCompile('org.springframework.boot:spring-boot-starter-test')
}

您可以创建可执行的JAR文件，并使用下面显示的Maven或Gradle命令运行Spring Boot应用程序 -

对于Maven，使用如下所示的命令 -

mvn clean install

在BUILD SUCCESS之后，您可以在目标目录下找到JAR文件。

对于Gradle，使用如下所示的命令 -

gradle clean build

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

现在，使用以下命令运行JAR文件

java –jar <JARFILE>

您可以在Tomcat端口8080上看到应用程序已启动。

现在点击URL http://localhost:8080/并查看输出Hello World。它应该如下所示 -

然后，您可以在控制台日志中看到远程主机和远程地址，如下所示 -