---
title: GeoServer二次开发-OWS服务(自定义模块)
date: 2021-04-25
author: ac
tags:
 - GeoServer
categories:
 - GIS
---

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。

<!--more-->

## 1. OWS 

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:

- Service
- Version
- Request - a service

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。

这些服务使用jar包中包含的Spring applicationContext.xml文件为Dispatcher进行配置。

## 2. OWS示例

现在我们开始来实现一个简单的OWS服务。

1. 新建一个Maven项目
2. 创建插件(plug-in)
3. 打包编译
4. 部署运行

### 新建一个Maven项目

![image-20210425135952027](../images/geoserver/image-20210425135952027.png)

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。

![image-20210425140151079](../images/geoserver/image-20210425140151079.png)

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：

```xml
<?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>org.geoserver</groupId>
    <artifactId>hello</artifactId>
    <packaging>jar</packaging>
    <version>1.0</version>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>

    <parent>
        <groupId>org.geoserver</groupId>
        <artifactId>community</artifactId>
        <version>2.18.1</version>
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.geoserver</groupId>
            <artifactId>gs-main</artifactId>
            <version>2.18.1</version>
        </dependency>
    </dependencies>
</project>
```

目录结构

```yaml
hello/
  + pom.xml
  + src/
    + main/
      + java/
```



### 创建插件(plug-in)

A plug-in is a collection of extensions realized as spring beans.

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`：

```java
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class HelloWorld {

    public HelloWorld() {
        // Do nothing
    }

    public void sayHello(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.getOutputStream().write("Hello World".getBytes());
    }
}
```

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。

创建`applicationContext.xml`文件，配置bean：

```xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    
    <!-- 将新建的HelloWorld服务类配置到Spring容器中   -->
    <bean id="helloService" class="HelloWorld"/>

    <!--  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  -->
    <bean id="helloService-1.0.0" class="org.geoserver.platform.Service">

        <!-- 服务的id，对应URL请求中的service名称 -->
        <constructor-arg index="0" value="hello"/>

        <!-- 服务对应的处理类 -->
        <constructor-arg index="1" ref="helloService"/>

        <!-- 服务的版本 -->
        <constructor-arg index="2" value="1.0.0"/>

        <!-- 服务的方法列表 -->
        <constructor-arg index="3">
            <list>
                <value>sayHello</value>
            </list>
        </constructor-arg>
    </bean>
</beans>
```

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：

```java
 public Service(String id, Object service, Version version, List<String> operations) {
     this(id, null, service, version, operations);
 }
```



目录结构：

```yaml
hello/
  + pom.xml
  + src/
    + main/
      + java/
        + HelloWorld.java
        + applicationContext.xml
```



### 打包编译

cmd进入项目根目录下，执行`mvn install`打包项目：

```java
hello>mvn install
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------< org.geoserver:hello >-------------------------
[INFO] Building hello 1.0
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- git-commit-id-plugin:2.1.15:revision (default) @ hello ---
[INFO]
[INFO] --- directory-maven-plugin:0.3.1:highest-basedir (directories) @ hello ---
[INFO] Highest basedir set to: E:\learning\OGC\geoserverdev\geoserver\geoserver-2.18.1\hello
[INFO]
[INFO] --- fmt-maven-plugin:2.4.0:format (default) @ hello ---
[debug] Using AOSP style
[INFO] Processed 1 files (1 reformatted).
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ hello ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 1 resource
[INFO] Copying 0 resource
[INFO]
[INFO] --- maven-compiler-plugin:3.8.0:compile (default-compile) @ hello ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to E:\learning\OGC\geoserverdev\geoserver\geoserver-2.18.1\hello\target\classes
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ hello ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 0 resource
[INFO] skip non existing resourceDirectory E:\learning\OGC\geoserverdev\geoserver\geoserver-2.18.1\hello\src\test\resources
[INFO]
[INFO] --- maven-compiler-plugin:3.8.0:testCompile (default-testCompile) @ hello ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-surefire-plugin:2.22.2:test (default-test) @ hello ---
[INFO]
[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ hello ---
[INFO] Building jar: E:\learning\OGC\geoserverdev\geoserver\geoserver-2.18.1\hello\target\hello-1.0.jar
[INFO]
[INFO] --- maven-jar-plugin:2.4:test-jar (default) @ hello ---
[INFO] Building jar: E:\learning\OGC\geoserverdev\geoserver\geoserver-2.18.1\hello\target\hello-1.0-tests.jar
[INFO]
[INFO] --- maven-source-plugin:2.2.1:jar-no-fork (attach-sources) @ hello ---
[INFO] Building jar: E:\learning\OGC\geoserverdev\geoserver\geoserver-2.18.1\hello\target\hello-1.0-sources.jar
[INFO]
[INFO] --- maven-source-plugin:2.2.1:test-jar-no-fork (attach-sources) @ hello ---
[INFO] No sources in project. Archive not created.
[INFO]
[INFO] --- maven-install-plugin:2.4:install (default-install) @ hello ---
[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
[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
[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
[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
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  3.689 s
[INFO] Finished at: 2021-04-25T14:20:52+08:00
[INFO] ------------------------------------------------------------------------

```

<img src="../images/geoserver/image-20210425144736264.png" alt="image-20210425144736264" style="zoom:50%;" />



### 部署运行

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。

在浏览器端发送请求验证是否部署成功：

`http://localhost:8080/geoserver/ows?request=sayHello&service=hello&version=1.0.0`

![image-20210425145312296](../images/geoserver/image-20210425145312296.png)

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：

- Service：服务的id
- Version：服务的版本
- Requrest：服务操作集合列表中方法名称；
- 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；

> 当两个service的id和version都相同时，可以认为这两个service相等。



## 参考文章

[1] Programming Guide https://docs.geoserver.org/latest/en/developer/programming-guide/index.html

[2] Implementing a simple OWS service https://docs.geoserver.org/latest/en/developer/programming-guide/ows-services/implementing.html