270 lines
9.4 KiB
Markdown
270 lines
9.4 KiB
Markdown
---
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title: GeoServer二次开发-OWS服务(自定义模块)
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date: 2021-04-25
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author: ac
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tags:
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- GeoServer
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categories:
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- GIS
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---
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本章介绍GeoServer Dispatcher如何在GeoServer中实现OWS服务，以及创建GeoServer 自定义模块的步骤，将其用作GeoServer扩展。
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<!--more-->
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## 1. OWS
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OGC定义了一系列Web协议，这些协议都遵循类似的设计（接口）。将这些共有的接口实现规范和标准参考抽离出来，就形成了OWS。OWS使用以下方法定义服务:
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- Service
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- Version
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- Request - a service
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GeoServer的`ows` 包的`org.geoserver.ows.Dispatcher` 类处理所有`OWS`的请求，同时Spring框架会为这些请求注入合适的实现。
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这些服务使用jar包中包含的Spring applicationContext.xml文件为Dispatcher进行配置。
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## 2. OWS示例
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现在我们开始来实现一个简单的OWS服务。
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1. 新建一个Maven项目
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2. 创建插件(plug-in)
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3. 打包编译
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4. 部署运行
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### 新建一个Maven项目
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将项目中的Maven指定为本地的安装路径，这样就可以引用之前源码打包的各模块的jar。
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在pom.xml文件中指定父级项目为`org.geoserver.community`、添加依赖以及指定打包方式：
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```xml
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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>org.geoserver</groupId>
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<artifactId>hello</artifactId>
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<packaging>jar</packaging>
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<version>1.0</version>
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<properties>
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<maven.compiler.source>8</maven.compiler.source>
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<maven.compiler.target>8</maven.compiler.target>
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</properties>
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<parent>
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<groupId>org.geoserver</groupId>
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<artifactId>community</artifactId>
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<version>2.18.1</version>
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</parent>
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<dependencies>
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<dependency>
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<groupId>org.geoserver</groupId>
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<artifactId>gs-main</artifactId>
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<version>2.18.1</version>
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</dependency>
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</dependencies>
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</project>
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```
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目录结构
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```yaml
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hello/
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+ pom.xml
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+ src/
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+ main/
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+ java/
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```
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### 创建插件(plug-in)
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A plug-in is a collection of extensions realized as spring beans.
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一个插件是通过Spring bean的方式实现的扩展集合。本例创建一个`HelloWorld.java`：
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```java
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import java.io.IOException;
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import javax.servlet.ServletException;
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import javax.servlet.http.HttpServletRequest;
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import javax.servlet.http.HttpServletResponse;
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public class HelloWorld {
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public HelloWorld() {
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// Do nothing
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}
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public void sayHello(HttpServletRequest request, HttpServletResponse response)
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throws ServletException, IOException {
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response.getOutputStream().write("Hello World".getBytes());
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}
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}
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```
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该服务相对简单。它提供了一个sayHello方法，接受一个HttpServletRequest和一个HttpServletResponse。这个方法的参数由org.geoserver.ows.Dispatcher自动注入。
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创建`applicationContext.xml`文件，配置bean：
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```xml
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<?xml version="1.0" encoding="UTF-8"?>
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<beans xmlns="http://www.springframework.org/schema/beans"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
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<!-- 将新建的HelloWorld服务类配置到Spring容器中 -->
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<bean id="helloService" class="HelloWorld"/>
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<!-- 在容器中配置一个对应的服务描述类，用于org.geoserver.ows.Dispatcher定位服务 -->
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<bean id="helloService-1.0.0" class="org.geoserver.platform.Service">
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<!-- 服务的id，对应URL请求中的service名称 -->
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<constructor-arg index="0" value="hello"/>
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<!-- 服务对应的处理类 -->
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<constructor-arg index="1" ref="helloService"/>
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<!-- 服务的版本 -->
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<constructor-arg index="2" value="1.0.0"/>
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<!-- 服务的方法列表 -->
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<constructor-arg index="3">
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<list>
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<value>sayHello</value>
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</list>
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</constructor-arg>
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</bean>
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</beans>
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```
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上面Spring是根据构造器的方式创建`org.geoserver.platform.Service`的实例bean的，对应的构造方法如下：
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```java
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public Service(String id, Object service, Version version, List<String> operations) {
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this(id, null, service, version, operations);
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}
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```
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目录结构：
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```yaml
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hello/
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+ pom.xml
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+ src/
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+ main/
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+ java/
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+ HelloWorld.java
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+ applicationContext.xml
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```
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### 打包编译
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cmd进入项目根目录下，执行`mvn install`打包项目：
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```java
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hello>mvn install
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[INFO] Scanning for projects...
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[INFO]
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[INFO] ------------------------< org.geoserver:hello >-------------------------
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[INFO] Building hello 1.0
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[INFO] --------------------------------[ jar ]---------------------------------
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[INFO]
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[INFO] --- git-commit-id-plugin:2.1.15:revision (default) @ hello ---
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[INFO]
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[INFO] --- directory-maven-plugin:0.3.1:highest-basedir (directories) @ hello ---
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[INFO] Highest basedir set to: E:\learning\OGC\geoserverdev\geoserver\geoserver-2.18.1\hello
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[INFO]
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[INFO] --- fmt-maven-plugin:2.4.0:format (default) @ hello ---
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[debug] Using AOSP style
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[INFO] Processed 1 files (1 reformatted).
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[INFO]
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[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ hello ---
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[INFO] Using 'UTF-8' encoding to copy filtered resources.
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[INFO] Copying 1 resource
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[INFO] Copying 0 resource
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[INFO]
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[INFO] --- maven-compiler-plugin:3.8.0:compile (default-compile) @ hello ---
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[INFO] Changes detected - recompiling the module!
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[INFO] Compiling 1 source file to E:\learning\OGC\geoserverdev\geoserver\geoserver-2.18.1\hello\target\classes
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[INFO]
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[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ hello ---
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[INFO] Using 'UTF-8' encoding to copy filtered resources.
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[INFO] Copying 0 resource
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[INFO] skip non existing resourceDirectory E:\learning\OGC\geoserverdev\geoserver\geoserver-2.18.1\hello\src\test\resources
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[INFO]
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[INFO] --- maven-compiler-plugin:3.8.0:testCompile (default-testCompile) @ hello ---
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[INFO] Nothing to compile - all classes are up to date
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[INFO]
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[INFO] --- maven-surefire-plugin:2.22.2:test (default-test) @ hello ---
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[INFO]
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[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ hello ---
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[INFO] Building jar: E:\learning\OGC\geoserverdev\geoserver\geoserver-2.18.1\hello\target\hello-1.0.jar
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[INFO]
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[INFO] --- maven-jar-plugin:2.4:test-jar (default) @ hello ---
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[INFO] Building jar: E:\learning\OGC\geoserverdev\geoserver\geoserver-2.18.1\hello\target\hello-1.0-tests.jar
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[INFO]
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[INFO] --- maven-source-plugin:2.2.1:jar-no-fork (attach-sources) @ hello ---
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[INFO] Building jar: E:\learning\OGC\geoserverdev\geoserver\geoserver-2.18.1\hello\target\hello-1.0-sources.jar
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[INFO]
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[INFO] --- maven-source-plugin:2.2.1:test-jar-no-fork (attach-sources) @ hello ---
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[INFO] No sources in project. Archive not created.
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[INFO]
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[INFO] --- maven-install-plugin:2.4:install (default-install) @ hello ---
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[INFO] Installing E:\learning\OGC\geoserverdev\geoserver\geoserver-2.18.1\hello\target\hello-1.0.jar to C:\Users\P53\.m2\repository\org\geoserver\hello\1.0\hello-1.0.jar
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[INFO] Installing E:\learning\OGC\geoserverdev\geoserver\geoserver-2.18.1\hello\pom.xml to C:\Users\P53\.m2\repository\org\geoserver\hello\1.0\hello-1.0.pom
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[INFO] Installing E:\learning\OGC\geoserverdev\geoserver\geoserver-2.18.1\hello\target\hello-1.0-tests.jar to C:\Users\P53\.m2\repository\org\geoserver\hello\1.0\hello-1.0-tests.jar
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[INFO] Installing E:\learning\OGC\geoserverdev\geoserver\geoserver-2.18.1\hello\target\hello-1.0-sources.jar to C:\Users\P53\.m2\repository\org\geoserver\hello\1.0\hello-1.0-sources.jar
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[INFO] ------------------------------------------------------------------------
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[INFO] BUILD SUCCESS
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[INFO] ------------------------------------------------------------------------
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[INFO] Total time: 3.689 s
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[INFO] Finished at: 2021-04-25T14:20:52+08:00
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[INFO] ------------------------------------------------------------------------
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```
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<img src="../images/geoserver/image-20210425144736264.png" alt="image-20210425144736264" style="zoom:50%;" />
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### 部署运行
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将打包好的hello.jar拷贝到GeoServer中的`webapps\geoserver\WEB-INF\lib` 中，重启GeoServer就完成了一个简单的OWS服务扩展。
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在浏览器端发送请求验证是否部署成功：
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`http://localhost:8080/geoserver/ows?request=sayHello&service=hello&version=1.0.0`
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回到上面开头说的OWS用来定义服务的方式，在`applicationContext.xml`文件中配置的`org.geoserver.platform.Service`类中定义服务的描述信息：
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- Service：服务的id
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- Version：服务的版本
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- Requrest：服务操作集合列表中方法名称；
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- Request ：在applicationContext.xml中根据构造器引用`org.geoserver.platform.Service`类的第四个集合参数中的方法名称；
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> 当两个service的id和version都相同时，可以认为这两个service相等。
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## 参考文章
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[1] Programming Guide https://docs.geoserver.org/latest/en/developer/programming-guide/index.html
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[2] Implementing a simple OWS service https://docs.geoserver.org/latest/en/developer/programming-guide/ows-services/implementing.html |