Java J2EE中的依赖查找

个人看法:设计依赖查找的设计模式,是为了解耦.

• 单一类型依赖查找
  • JNDI javax.naming.Context#lookup
  • JavaBeans java.beans.beancontext.BeanContext
• 集合类型依赖查找
  • java.beans.beancontext.BeanContext#getCurrentServiceSelectors
• 层析性依赖查找

Springboot中使用JNDI

JNDI即Java Naming and Directory Interface（JAVA命名和目录接口），那么java命名目的就是为了记录一些不方便记录的内容，就像人的名字或DNS中的域名与IP的关系。

两种模式

1. Springboot Embedded Tomcat(嵌入Tomcat)使用JNDI
2. Springboot WAR 使用JNDI

1. Springboot Embedded Tomcat(嵌入Tomcat)使用JNDI

• 启用默认禁用的JNDI命名。
• 构建一个ContextResource对象，然后添加到Context对象中

java:/comp/env/ 固定写法

JndiConfig.java

package com.rumenz;

import org.apache.catalina.Context;
import org.apache.catalina.startup.Tomcat;
import org.apache.tomcat.util.descriptor.web.ContextResource;
import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory;
import org.springframework.boot.web.embedded.tomcat.TomcatWebServer;
import org.springframework.boot.web.servlet.server.ServletWebServerFactory;
import org.springframework.context.annotation.Bean;
import org.springframework.jndi.JndiObjectFactoryBean;
import org.springframework.stereotype.Component;
import javax.naming.NamingException;
import javax.sql.DataSource;
@Component
public class JndiConfig {

    @Bean
    public ServletWebServerFactory servletContainer() {
        TomcatServletWebServerFactory tomcatServletWebServerFactory = new TomcatServletWebServerFactory() {
            @Override
            protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
                tomcat.enableNaming(); //启用默认禁用的JNDI命名
                return super.getTomcatWebServer(tomcat);

            }
            //数据库配置信息可以配置在文件中,数据库发生变动,只需修改配置文件,而不用修改代码.
            @Override
            protected void postProcessContext(Context context) {
                ContextResource resource = new ContextResource();
                resource.setName("jdbcMydb");
                resource.setType(DataSource.class.getName());
                resource.setProperty("driverClassName", "com.mysql.jdbc.Driver");
                resource.setProperty("url", "jdbc:mysql://127.0.0.1:3306/test");
                resource.setProperty("username", "root");
                resource.setProperty("password","root1234");
                context.getNamingResources().addResource(resource);
            }
        };
        return tomcatServletWebServerFactory;
    }
    @Bean
    public DataSource jndiDataSource() throws IllegalArgumentException,
            NamingException {
        JndiObjectFactoryBean bean = new JndiObjectFactoryBean();           // create JNDI data source
        bean.setJndiName("java:/comp/env/jdbcMydb");  // jndiDataSource is name of JNDI data source
        bean.setProxyInterface(DataSource.class);
        bean.setLookupOnStartup(true);
        bean.afterPropertiesSet();
        return (DataSource) bean.getObject();
    }

}

MysqlTest.java

package com.rumenz;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.boot.CommandLineRunner;
import org.springframework.context.ApplicationContext;
import org.springframework.stereotype.Component;

import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;

@Component
public class MysqlTest implements ApplicationRunner {
    public static DataSource dataSource = null;

   static {
       Context context = null;
       try {
           context = new InitialContext();
       } catch (NamingException e) {
           e.printStackTrace();
       }
       //根据资源名称搜索
       try {
           dataSource = (DataSource)context.lookup("java:/comp/env/jdbcMydb");
       } catch (NamingException e) {
           e.printStackTrace();
       }
       System.out.println("static-----");
   }

    public void run(ApplicationArguments args) throws Exception {
        System.out.println("run---------");
        Statement stmt = null;
        try {
            Connection conn = dataSource.getConnection();
            //查询
            stmt = conn.createStatement();
            String sql = "SELECT id,name FROM qq limit 1";
            ResultSet rs = stmt.executeQuery(sql);
            while(rs.next()){
                int id  = rs.getInt("id");
                String name = rs.getString("name");
                System.out.print("id: " + id);
                System.out.println(", name: " + name);
            }
            rs.close();
            stmt.close();
            conn.close();
        } catch (Exception e) {
          e.printStackTrace();
        }
    }
}

源码:https://github.com/mifunc/springboot-jndi-Embedded-Tomcat

2.Springboot WAR 使用JNDI

打包成war包放到tomcat,需要修改tomcat/conf/context.xml和tomcat/conf/server.xml

tomcat/conf/context.xml

tomcat/conf/server.xml

业务代码

JNDIController.java

package com.rumenz.controller;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import javax.sql.DataSource;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class JNDIController {
    @Autowired
    private DataSource dataSource;
    
    @GetMapping("/test")
    public String test() {
        try {
            Connection conn = dataSource.getConnection();
            Statement stmt = conn.createStatement();
            String sql = "SELECT id,name FROM qq limit 1";
            ResultSet rs = stmt.executeQuery(sql);
            while(rs.next()){
                int id  = rs.getInt("id");
                String name = rs.getString("name");
                System.out.print("id: " + id);
                System.out.println(", name: " + name);
            }
            rs.close();
            stmt.close();
            conn.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }

}

源码:https://github.com/mifunc/Springboot-jndi-war-Tomcat

java.beans.beancontext.BeanContext(单一类型依赖查找/集合类型依赖查找)

• 单一类型依赖查找
  • java.beans.beancontext.BeanContextServicesSupport#getService
• 集合类型依赖查找
  • java.beans.beancontext.BeanContextServicesSupport#getCurrentServiceSelectors

层析性依赖查找

多个BeanContext相互为父子关系. 一个service的依赖有可能在多个BeanContext

image.png