獲取資源文件有三種方式

採用 ServletContext對象獲取
採用ResourceBundle類來獲取
採用類加載器獲取

分別獲取圖中的a、b、c.properties：java

文件內容分別是：a=a;b=b;c=cweb

重點：注意獲取圖中文件的路徑寫法，不是直接看ide中的位置，而是要看項目發佈到tomcat以後該文件所在的位置。tomcat

1、採用 ServletContext對象獲取

優勢：任意文件，任意路徑缺點：必須有web環境服務器

獲取文件真實（服務器）路徑：String getRealPath()markdown

1.1 獲取web目錄下資源b.properties

寫法：/b.propertieside

package com.hcx.web.servlet;

import javax.servlet.ServletContext;
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.FileReader;
import java.io.IOException;
import java.util.Properties;

/** * Created by hongcaixia on 2019/11/19. */
@WebServlet("/getResourceFileServlet")
public class GetResourceFileServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        getWebResource();
    }
    /** * 獲取web下的資源b.properties,查看文件發佈到tomcat的位置爲/b.properties */
    public void getWebResource(){
        ServletContext servletContext = this.getServletContext();
        String realPath = servletContext.getRealPath("/b.properties");
        //文件的路徑是：D:\WorkSpaces\IDEAWS\tomcatdemo\out\artifacts\tomcatdemo_war_exploded\b.properties
        System.out.println("文件的路徑是："+realPath);
        Properties properties = new Properties();
        try {
            properties.load(new FileReader(realPath));
        } catch (IOException e) {
            e.printStackTrace();
        }
        Object b = properties.get("b");
        //獲取到的key是：b
        System.out.println("獲取到的key值是："+b);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

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項目啓動後從日誌中找到CATALINA_BASE值：C:\Users\HCX\.IntelliJIdea2017.2\system\tomcat\Tomcat_8_5_0_tomcatdemo oop

CATALINA_HOME和CATALINA_BASE的區別: 簡單的說，CATALINA_HOME是Tomcat的安裝目錄，CATALINA_BASE是Tomcat的工做目錄。若是想要運行Tomcat的多個實例，可是不想安裝多個Tomcat軟件副本。那麼能夠配置多個工做目錄，每一個運行實例獨佔一個工做目錄，可是共享同一個安裝目錄。詳細介紹能夠參考我以前寫的Tomcat文章，裏面介紹了應用程序的部署方式：blog.csdn.net/CSDN_GIA/ar…this

因此，b.properties文件位於服務器的根目錄下，寫法爲 /b.properties

1.2 獲取WEB-INF目錄下資源c.properties

從上一個例子能夠看出,/表明的服務器的路徑是：D:\WorkSpaces\IDEAWS\tomcatdemo\out\artifacts\tomcatdemo_war_exploded url

因此 WEB-INF下資源寫法爲： /WEB-INF/c.properties

/** * 獲取WEB-INF下資源c.properties */
    public void getWebINFOResource() {
        ServletContext servletContext = this.getServletContext();
        String realPath = servletContext.getRealPath("/WEB-INF/c.properties");
        //文件的路徑是：D:\WorkSpaces\IDEAWS\tomcatdemo\out\artifacts\tomcatdemo_war_exploded\WEB-INF\c.properties
        System.out.println("文件的路徑是：" + realPath);
        Properties properties = new Properties();
        try {
            properties.load(new FileReader(realPath));
        } catch (IOException e) {
            e.printStackTrace();
        }
        Object c = properties.get("c");
        //獲取到的key值是：c
        System.out.println("獲取到的key值是：" + c);
    }
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1.3 獲取src目錄下資源a.properties

src下的全部資源未來會被放到WEB-INF目錄下的classes目錄下寫法：/WEB-INF/classes/a.propertiesspa

public void getSrcResource() {
        ServletContext servletContext = this.getServletContext();
        String realPath = servletContext.getRealPath("/WEB-INF/classes/a.properties");
        //文件的路徑是：D:\WorkSpaces\IDEAWS\tomcatdemo\out\artifacts\tomcatdemo_war_exploded\WEB-INF\classes\a.properties
        System.out.println("文件的路徑是：" + realPath);
        Properties properties = new Properties();
        try {
            properties.load(new FileReader(realPath));
        } catch (IOException e) {
            e.printStackTrace();
        }
        Object a = properties.get("a");
        //獲取到的key值是：a
        System.out.println("獲取到的key值是：" + a);
    }
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2、採用ResourceBundle類來獲取

優勢：簡單方便缺點：

只能拿取properties文件

只能拿取非web環境下的資源（即src目錄下的）

ResourceBundle類：該類（抽象類）專門用來加載資源，還能夠處理一些國際化的東西

2.1 獲取src目錄下資源a.properties

public void getSrcResource() {
        //獲取ResourceBundle對象(專門用來獲取properties文件的信息,因此不用加後綴名.properties)
        ResourceBundle resourceBundle = ResourceBundle.getBundle("a");
        String a = resourceBundle.getString("a");
        System.out.println("src下資源文件：" + a);

        //獲取ResourceBundle對象(專門用來獲取properties文件的信息,因此不用加後綴名.properties)
        ResourceBundle resourceBundle2 = ResourceBundle.getBundle("com.hcx.web.d");
        String d = resourceBundle2.getString("d");
        System.out.println("src下資源文件：" + d);
    }
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3、採用類加載器獲取

優勢：任意文件，任意路徑缺點：編寫稍顯麻煩

類加載器： 一個java文件，編寫好以後是源碼，後綴名是.java，要將這個源碼首先採用編譯命令javac把其編譯爲.class文件，該.class文件位於硬盤上，在運行時，須要把.class文件加載到虛擬機裏運行，就用類加載器來加載，類加載器的主要目的就是將字節碼文件加載到內存裏，而後運行字節碼文件

獲取類加載器的方式

經過類名： 類名.class.getClassLoader()
經過對象： this.getClass().getClassLoader()
Class.forName()： Class.forName("類名").getClassLoader()

注意： this.getClass().getClassLoader().getResource("/");是去類路徑去加載資源，即classes目錄下：

3.1 獲取web目錄下資源b.properties

public void getWebResourceByClassLoader(){
        //url：file:/D:/WorkSpaces/IDEAWS/tomcatdemo/out/artifacts/tomcatdemo_war_exploded/WEB-INF/classes/
        URL url = this.getClass().getClassLoader().getResource("/");
        InputStream resourceAsStream = this.getClass().getClassLoader().getResourceAsStream("../../b.properties");

        Properties properties = new Properties();
        try {
            properties.load(resourceAsStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
        String b = properties.getProperty("b");
        System.out.println(b);

    }
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3.2 獲取WEB-INF目錄下資源c.properties

public void getWebInfoResourceByClassLoader(){
        //url：file:/D:/WorkSpaces/IDEAWS/tomcatdemo/out/artifacts/tomcatdemo_war_exploded/WEB-INF/classes/
        URL url = this.getClass().getClassLoader().getResource("/");
        InputStream resourceAsStream1 = this.getClass().getClassLoader().getResourceAsStream("../../WEB-INF/c.properties");

        Properties properties = new Properties();
        try {
            properties.load(resourceAsStream1);
        } catch (IOException e) {
            e.printStackTrace();
        }
        String c = properties.getProperty("c");
        System.out.println(c);
    }
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3.3 獲取src目錄下資源a.properties

package com.hcx.web.servlet;

import javax.servlet.ServletContext;
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.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;
import java.util.ResourceBundle;

/** * Created by hongcaixia on 2019/11/19. */
@WebServlet("/getResourceFileServlet")
public class GetResourceFileServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        getSrcResourceByClassLoader();
    }

    public void getSrcResourceByClassLoader(){
        //獲取類加載器方式：
        /** * 1.經過類名:ClassLoader classLoader = GetResourceFileServlet.class.getClassLoader(); * 2.經過對象：ClassLoader classLoader = this.getClass().getClassLoader(); * 3.經過Class.forName():ClassLoader classLoader = Class.forName("GetResourceFileServlet").getClassLoader(); */
        InputStream resourceAsStream = this.getClass().getClassLoader().getResourceAsStream("a.properties");
        Properties properties = new Properties();
        try {
            properties.load(resourceAsStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
        String a = properties.getProperty("a");
        System.out.println(a);
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

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Java中獲取資源文件三種方式