The third stage: Day17 jsonp global exception handling mechanism httpclient SOA idea RPC calls zookeeper Dubbo

Half bump 2020-11-09 16:56:08
stage day17 day jsonp global

1.JSONP Global exception handling mechanism

1.1 Problem specification

When the back-end server execution error , Global exception handling is performed . however JSONP The call requirements of the request for return type callback(JSON) structure . So we need to reconstruct the return value structure type of global exception handling .
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1.2 Edit global exception handling mechanism

`package com.jt.aop;
import com.fasterxml.jackson.databind.util.JSONPObject;
import com.jt.vo.SysResult;
import org.springframework.util.StringUtils;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestControllerAdvice;
import javax.servlet.http.HttpServletRequest;
import java.sql.SQLException;
//@ControllerAdvice // Intercept controller layer
@RestControllerAdvice // Defines the class for handling global exceptions AOP= Abnormal notice
public class SystemAOP {
* Methods for defining global exceptions When something goes wrong , Program start execution The parameters are general class type
* If something goes wrong , You should output abnormal information , Then return the error data .
* Rules for solving cross domain global exception handling : Cross domain of Jingtao project is to use JSONP. http://xxxx?callback=xxxxx
* If the request contains callback Parameters Think it is JSONP Cross-domain request .
* difficulty : How to get callback What about parameters? ??/
public Object systemAop(Exception e, HttpServletRequest request){
String callback = request.getParameter("callback");
// Normal method call mode
// Prove to be jsonp Cross-domain request
return new JSONPObject(callback,;


2.1 Business needs

Business description : As some operations , Data may be processed in business , After that, the server communicates with the server .
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2.2 HttpClient Introduce

HTTP The agreement may be now Internet Most used on 、 The most important agreement , More and more Java Applications need to go directly through HTTP Protocol to access network resources . Although in JDK Of java net Access is already provided in the package HTTP Basic functions of the protocol , But for most applications ,JDK The functions provided by the library itself are not rich and flexible enough .HttpClient yes Apache Jakarta Common Sub projects under , To provide efficient 、 Abreast of the times 、 Feature rich support HTTP Client programming toolkit for protocol , And it supports HTTP Latest version and suggestions of the agreement .HttpClient It has been applied in many projects , such as Apache Jakarta Two other open source projects famous in Cactus and HTMLUnit It's all used HttpClient. Now? HttpClient The latest version is HttpClient 4.5 .6(2015-09-11)

summary : stay java Agents can be used internally httpClient launch http Request access to the server for resources .( Tools API)

2.3 HttpClient Introductory cases

2.3.1 introduce jar package

 `<!-- add to httpClient jar package -->

2.3.2 Editing tests API

`package com.jt;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.methods.HttpPut;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;
import org.junit.jupiter.api.Test;
public class HttpClientTest {
* requirement : stay java Inside the code , Get Baidu's page .
* Implementation steps :
* 1. Determine the target address :
* 2. establish httpClient Client object
* 3. Create request type
* 4. launch http request . And get the result of the response . Then judge whether the status code is 200 If it is equal to 200 The request is correct
* 5. If the request is correct, the response value information is obtained dynamically . After that, the data is processed again ....
* */
public void testGet() throws IOException {
String url = "";
HttpClient httpClient = HttpClients.createDefault();
HttpGet httpGet = new HttpGet(url);
HttpResponse httpResponse = httpClient.execute(httpGet);
if(httpResponse.getStatusLine().getStatusCode() == 200) {
// Indicates that the user request is correct
// Get the return value data
HttpEntity httpEntity = httpResponse.getEntity();
String result = EntityUtils.toString(httpEntity, "UTF-8");

2.4 HttpClient Strengthen the case

2.4.1 The case requires

Users use the web address Required httpClient The way , obtain jt-manage Product information in after json In the form of strings .
jt-web Server access jt-manage When the website

2.4.2 Editor's desk HttpClientController

`package com.jt.controller;
import com.jt.pojo.Item;
import com.jt.service.HttpClientService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.List;
public class HttpClientController {
private HttpClientService httpClientService;
* Get back end manage Product data information in
public List<Item> getItems(){
return httpClientService.getItems();

2.4.2 Editor's desk HttpClientService

`package com.jt.service;
import com.jt.pojo.Item;
import com.jt.util.ObjectMapperUtil;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;
import org.springframework.stereotype.Service;
import org.springframework.util.StringUtils;
import java.util.ArrayList;
import java.util.List;
public class HttpClientServiceImpl implements HttpClientService{
public List<Item> getItems() {
List<Item> itemList = new ArrayList<>();
//1. Define the remote access URL
String url = "";
HttpClient httpClient = HttpClients.createDefault();
HttpGet httpGet = new HttpGet(url);
try {
HttpResponse httpResponse = httpClient.execute(httpGet);
if(httpResponse.getStatusLine().getStatusCode() == 200){
String result =
EntityUtils.toString(httpResponse.getEntity(), "UTF-8");
//result yes jt-manage by jt-web Back to List<Item> Of JSON strand
itemList = ObjectMapperUtil.toObj(result, itemList.getClass());
} catch (IOException e) {
throw new RuntimeException(e);
return itemList;

2.4.3 Editing backstage HttpClientController

`package com.jt.web.controller;
import com.jt.pojo.Item;
import com.jt.service.ItemService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.List;
public class HttpClientController {
private ItemService itemService;
* url Request address :
public List<Item> getItems(){
return itemService.getItems();

2.4.4 Editing backstage HttpClientService

public List<Item> getItems() {
return itemMapper.selectList(null);

2.4.5 Page effect display

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  1. SOA thought ( Standards for micro service agent editing )


Service Oriented Architecture (SOA) It's a component model , It will be different functional units of the application ( It's called service ) To break up , And through well-defined interfaces and protocols between these services . Interfaces are defined in a neutral way , It should be independent of the hardware platform that implements the service 、 Operating system and programming language . This allows services built into a variety of systems to interact in a unified and common way .

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  1. RPC Introduction to ideas


RPC yes Remote procedure call (Remote Procedure Call) Abbreviated form .
summary :

  1. When you can't finish a business, you can't do it directly , Business that needs help from a third party .
  2. Use RPC when " Feeling " You are calling your own methods to complete the business .

5. Micro service idea

The core : 1. Distributed thinking ( Demolition ) 2. automation (HA, automation )

5.1 Traditional project issues

1. If the nginx The way Load balancing , When the number of services changes , All have to be modified manually nginx.conf The configuration file . Not smart enough .
2. All requests will pass nginx Server as transit . If nginx Once the server goes down , It directly affects the whole system .nginx It's better to just do simple Reverse proxy that will do
The traditional way Not smart enough …

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5.2 How to call microservices

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Call step :
1. Write service information to registry (1. The service name 2. service IP Address 3. port )
2. The registry received server information , Maintain service list data dynamically .
3. When consumers start, they will link to the registry . Purpose to obtain service list data .
4. The registry will synchronize the service list data to consumers , And save it locally to consumers . It is convenient to call later .
5. When the consumer starts a business call , Load balancing will be performed according to the known service information , Visit the service provider .
6. When a service provider goes down , There is a heartbeat detection mechanism with the registry . So the list of services will be maintained dynamically .
7. When the list of services in the registry changes , It will broadcast all over the network Inform all consumers Update local service list .

5.3 Zookeeper Registration Center Introduction

ZooKeeper It's a distributed one , Open source distributed application coordination service , yes Google Of Chubby An open source implementation , yes Hadoop and Hbase Important components . It is a software that provides consistency services for distributed applications , The features provided include : Configuration maintenance 、 Domain name service 、 Distributed synchronization 、 Group service, etc .
ZooKeeper The goal is to encapsulate complex, error-prone, critical services , Will be simple to use interface and efficient performance 、 A stable system is provided to the user .
ZooKeeper Contains a simple set of primitives , Provide Java and C The interface of .
ZooKeeper In the code version , Provides distributed exclusive locks 、 The election 、 The interface of the queue , Code in $zookeeper_homesrcrecipes. The distribution locks and queues are Java and C Two versions , The election is just Java edition .
Generalization : ZK The main task is Service scheduling , The ability to provide consistency .

5.4 About cluster knowledge introduction

5.4.1 The smallest cluster units are

The formula : The number of surviving nodes > N/2 Clusters can create
1 platform : 1-1 > 1/2 fake
2 platform : 2-1> 2/2 fake
3 platform : 3-1> 3/2 correct
4 platform : 4-1> 4/2 correct

Conclusion : Build the smallest unit of a cluster 3 platform .

5.4.2 Why clusters are usually odd

  1. 3 At most, the cluster has several downtime Cluster works Most downtime 1 platform
  2. 4 At most, several clusters can work normally Most downtime 1 platform
    If you implement the same function Odd numbers are better .

5.5 About zk Cluster election rules

principle : myid Maximum priority myid The higher the value, the easier it is to be the host . More than half of them agree to be elected host
subject : ask 1,2,3,4,5,6,7 Start in turn ask 1: Who is the host 4 When the host
ask 2: Who can never be elected host ??? 1 2 3

6 Homework

preview Dubbo frame
Modify the code :
Modify the entry case dubbo Project pom.xml file
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 `1. Project version `

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2. modify module label
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3. Import the project
take dubbo-jt Paste project to workspace and jt Level Then right click add Maven…
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本文为[Half bump]所创,转载请带上原文链接,感谢

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