GeoTools is an open source Java library for authoring GIS software and applications. <\/p>\n\n\n\n
https:\/\/geotools.org<\/a><\/p>\n\n\n\n It is a fully equipped library adhering to the Open Geospatial Consortium (OGC) standards and providing graphical user interface (GUI). <\/p>\n\n\n\n https:\/\/docs.geotools.org\/latest\/userguide\/welcome\/standards.html<\/a><\/p>\n\n\n\n This lecture demonstrates techniques for using GeoTools in a Grails app through the sequence of three projects:<\/p>\n\n\n\n The final project, grails-geotools, focuses on using shapefiles for querying geographic information and rendering the information in a view. <\/p>\n\n\n\n Before studying these projects, you should have some acquaintance with GeoTools and GIS terminology. I recommending doing a few lectures at GeoTools, at a minimum:<\/p>\n\n\n\n GeoTools developers prefer to use Maven for their build tool.<\/p>\n\n\n\n https:\/\/maven.apache.org<\/a><\/p>\n\n\n\n Maven is one of the original Java build tools and is a substitute for Gradle. It is worthwhile becoming acquainted with it. Fortunately you can download it using SDKMAN.<\/p>\n\n\n\n https:\/\/sdkman.io<\/a><\/p>\n\n\n\n Look for it using <\/p>\n\n\n\n In the Maven Quickstart, you will learn how to display a shapefile in a SWING map. Shapefiles is ESRI standard for a geodatabase. The shapefile and the associated “side car” files are ESRI proprietary formats for representing geography and associated attributes. You can think of it as a geodatabase. <\/p>\n\n\n\n A special note: The current version of GeoTools requires Java 11.<\/p>\n\n\n\n In the Feature Tutorial, you will gain more understanding of shapefiles by making shapefiles from a CSV file. Each item in the shape is called a “feature”. The feature has a “geometry” and associated properties. <\/p>\n\n\n\n In the Query Tutorial, you learn how to make queries into the Shapefile. Rather you make queries into the datastore that you build from the shapefiles. The queries can be geographical such as does a feature contain a point. Although relational databases use SQL, the Query Tutorial uses the Common Query Language, CQL. <\/p>\n\n\n\n After completing the three tutorials, you should realize that there are still some challenges for using GeoTools in a Grails app. <\/p>\n\n\n\n The first project in this lecture demonstrates how to build a GeoTools app using Gradle. It is not a difficult challenge, but requires knowledge of both Maven and Gradle. The app is simple. It reads a shapefile, builds a datastore and then query it. <\/p>\n\n\n\n The best way for Grails controllers to access datastores is from a service. But we don’t want each query into the datastore to reread and load the shapefile. So our program should create a Java object representing the datastore. But this leads to another problem, how should the Service access the datastore object? The technology to use is called “Spring Beans”. The second project in this lecture will briefly explain the Spring Bean technology and how to use them in a Grails app.<\/p>\n\n\n\n The final project in this lecture combines the two previous projects to render geographical information in a view. A bean will represent the datastore built from the shapefiles and a service will make queries into the feature sources. <\/p>\n\n\n\n You can clone the code at:<\/p>\n\n\n\n https:\/\/github.com\/2024-UI-SP\/GeoTools-Lecture<\/a><\/p>\n\n\n\n The gradle-geotools project demonstrates developing a simple GeoTools app in a Gradle project. It was initialized in the gradle-geotools directory with Gradle 7.2 using Java 11. We make the basic Gradle project by entering<\/p>\n\n\n\n The script will ask questions about the project: <\/p>\n\n\n\n The script makes a “hello world” app. The code for the class is located in To make the project we only need to <\/p>\n\n\n\n First, we edit The code is the simplest code that I could write to load a shapefile to create the datastore, make a few queries into the feature source, and process the feature collection resulting from the queries<\/p>\n\n\n\n Note the Java File is made using https:\/\/docs.oracle.com\/javase\/6\/docs\/api\/java\/lang\/Class.html#getResource(java.lang.String)<\/a><\/p>\n\n\n\n https:\/\/stackoverflow.com\/questions\/6608795\/what-is-the-difference-between-class-getresource-and-classloader-getresource<\/a><\/p>\n\n\n\n Now we add the shapefiles. Conveniently, the initializing script made a resources directory in app\/src\/main\/. But we need the path to match the class package, so we make http:\/\/udig.refractions.net\/files\/docs\/<\/a><\/p>\n\n\n\n Note you should use the code from the Query Tutorial to examine the shapefiles and learn the property names. <\/p>\n\n\n\n The code uses a CQL string to make the filter. Because we want only a few properties of the features, we need to construct a To examine the feature collection from the result of the query, the code MUST use To summarize, the code needs to: <\/p>\n\n\n\n Finally to build the project, we need to edit I determined these unusual declarations from <\/p>\n\n\n\n https:\/\/docs.gradle.org\/current\/userguide\/declaring_repositories.html#maven_repository_filtering<\/a><\/p>\n\n\n\n and inspecting the mvn declarations in the GeoTools tutorials. Also important is that these declarations must be placed before the maven central declaration because the javax.mediajai_core POM is broken in maven central. Gradle searches the repositories in order so if maven central is searched first. It discovers the POM for the package, but the package does not exist. This brakes Maven and Gradle. <\/p>\n\n\n\n https:\/\/stackoverflow.com\/questions\/26993105\/i-get-an-error-downloading-javax-media-jai-core1-1-3-from-maven-central<\/a><\/p>\n\n\n\n Now add the project dependencies in the dependencies section<\/p>\n\n\n\n Most of the classes used by We are done and can run the project with<\/p>\n\n\n\n Look for the print output in the console. Study the code. Try writing a different query and processing the resulting feature collection.<\/p>\n\n\n\n This project demonstrates how Spring Beans are used in a Grails project. The bean only prints out to the terminal. We want to learn: <\/p>\n\n\n\n The Grails documentation for Spring Beans does not explain how to define and use beans.<\/p>\n\n\n\n https:\/\/docs.grails.org\/6.2.0\/guide\/single.html#spring<\/a><\/p>\n\n\n\n We have to study the Spring documentation to learn more about beans: <\/p>\n\n\n\n https:\/\/docs.spring.io\/spring-framework\/reference\/core\/beans\/introduction.html<\/a><\/p>\n\n\n\n You will want to read more: <\/p>\n\n\n\n https:\/\/docs.spring.io\/spring-framework\/reference\/core\/beans\/basics.html<\/a><\/p>\n\n\n\n https:\/\/docs.spring.io\/spring-framework\/reference\/core\/beans\/definition.html<\/a><\/p>\n\n\n\n https:\/\/docs.spring.io\/spring-framework\/reference\/core\/beans\/factory-scopes.html<\/a><\/p>\n\n\n\n If the Spring documentation is too technical, you may find this stackoverflow post more gentle.<\/p>\n\n\n\n https:\/\/stackoverflow.com\/questions\/17193365\/what-in-the-world-are-spring-beans<\/a><\/p>\n\n\n\n The basic goal for the bean framework is that the developer should not have to worry about managing when and how to instantiate simple Java objects (called beans) and other classes in the application have access to the beans. Rather the “container” manages instantiating beans and making easy access to the instantiated bean for the other classes in the application. For this to happen properly, naturally, the developer needs to configure and register the bean with the “container”. Configuration includes: <\/p>\n\n\n\n Traditionally Spring used XML in a resources\/spring.xml file to configure the bean. Grails uses Groovy to configure beans in the You should realize that in a Grails project almost all groovy classes are beans, this includes:<\/p>\n\n\n\n Grails manages configuration of these beans.<\/p>\n\n\n\n Now we can look at the code. The basic Grail app was made with Grails 5.3 and Java 11 by entering<\/p>\n\n\n\n This creates a simple web app using the grails.bean package name.<\/p>\n\n\n\n First we will study a simple bean. The class files that you make yourself are located in src\/main\/groovy followed by the package directories. In this case<\/p>\n\n\n\n where “grails\/bean\/” is the package directory. <\/p>\n\n\n\n This bean has only two attributes, After writing the bean definition, you can run the application, but nothing will happen, although it will be compiled. <\/p>\n\n\n\n To instantiate bean, we need to configure and register it in \n
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sdk list mvn<\/pre>\n\n\n\n
The Challenge<\/h1>\n\n\n\n
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gradle-geotools<\/h1>\n\n\n\n
gradle init<\/pre>\n\n\n\n
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app\/src\/main\/gradle\/geotools\/App.java<\/code>. You can run the “hello world” app by entering<\/p>\n\n\n\n.\/gradlew run<\/pre>\n\n\n\n
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app\/src\/main\/java\/gradle\/geotools\/App.java<\/code><\/li>\n\n\n\napp\/src\/main\/resources\/gradle\/geotools\/<\/code><\/li>\n\n\n\napp\/build.gradle<\/code><\/li>\n<\/ol>\n\n\n\napp\/src\/main\/java\/gradle\/geotools\/App.java<\/code>. We replace the code with: <\/p>\n\n\n\n\/*\n * This Java source file was generated by the Gradle 'init' task.\n *\/\npackage gradle.geotools;\n\n\/\/ The following imports are for working with files\nimport java.io.File;\nimport java.net.URL;\n\n\/\/ The following imports are for making the data store and source\nimport org.geotools.api.data.FileDataStore;\nimport org.geotools.api.data.FileDataStoreFinder;\nimport org.geotools.api.data.SimpleFeatureSource;\n\n\/\/ The following imports are for making the query\nimport org.geotools.filter.text.cql2.CQL; \/\/ this needs gt-swing dependency\n\nimport org.geotools.api.filter.Filter;\n\nimport org.geotools.data.simple.SimpleFeatureCollection;\nimport org.geotools.data.simple.SimpleFeatureIterator;\nimport org.geotools.api.feature.simple.SimpleFeature;\nimport org.geotools.api.feature.type.FeatureType;\n\nimport org.geotools.api.data.Query;\n\npublic class App {\n\n public static void main(String[] args) throws Exception {\n System.out.println(\"Running App.main() \\n\");\n\n \/*\n * Make the data store and feature source\n *\/\n \/\/ Get the shapefile using getResource()\n URL url = App.class.getResource(\"countries.shp\");\n \/\/ Just to make sure we got the right file\n System.out.println(\"URL: \" + url+ \"\\n\"); \n File file = new File(url.toURI());\n\n \/\/ Use the file to make the data store using FileDataStoreFinder\n FileDataStore store = FileDataStoreFinder.getDataStore(file);\n \/\/ Get the feature source from the store using getFeatureSource()\n SimpleFeatureSource source = store.getFeatureSource();\n\n \/\/ Do some printing \n String typeName = store.getTypeNames()[0]; \/\/ There is only one type\n System.out.println(\"typeName is the name of datastore. It is almost always the name of the shapefile.\");\n System.out.println(\"typeName: \" + typeName + \"\\n\");\n FeatureType schema = source.getSchema();\n System.out.println(\"schema is the list of shapefile's attributes and types\");\n System.out.println(\"schema: \" + schema + \"\\n\");\n \n \/*\n * Make the query and filter to show all countries and population\n *\/\n System.out.println(\"Result from querying for all countries and population\");\n String cqlString = \"include\"; \/\/ Include all features\n Filter filter = CQL.toFilter(cqlString);\n Query query = new Query(typeName, filter, new String[] { \"CNTRY_NAME\", \"POP_CNTRY\" });\n System.out.println(\"query: \" + query + \"\\n\");\n\n \/\/ Get the features, i.e. the \"result set\"\n SimpleFeatureCollection features = source.getFeatures(query);\n\n try (SimpleFeatureIterator iterator = features.features()) {\n while (iterator.hasNext()) {\n SimpleFeature feature = iterator.next();\n \/\/ process feature\n for ( Object value : feature.getAttributes() ) {\n System.out.print(value + \" \");\n }\n System.out.println();\n }\n }\n System.out.println(\" \\n \");\n\n \/*\n * Make the query and filter to find the country that contains the a point.\n *\/\n System.out.println(\"Result from querying for the country that contains a point\");\n filter = CQL.toFilter(\"contains(the_geom, POINT(-100 40))\"); \/\/ Note logitude first\n query = new Query(typeName, filter, new String[] { \"CNTRY_NAME\", \"POP_CNTRY\" });\n System.out.println(\"query: \" + query + \"\\n\");\n\n \/\/ process the features. All this for a single item because features is a collection\n features = source.getFeatures(query);\n try (SimpleFeatureIterator iterator = features.features()) {\n while (iterator.hasNext()) {\n SimpleFeature feature = iterator.next();\n for ( Object value : feature.getAttributes() ) {\n System.out.print(value + \" \");\n }\n System.out.println();\n }\n }\n System.out.println(\" \\n \");\n } \n}\n<\/pre>\n\n\n\nclass.getResources<\/code><\/p>\n\n\n\n URL url = App.class.getResource(\"countries.shp\");\n \/\/ Just to make sure we got the right file\n System.out.println(\"URL: \" + url+ \"\\n\"); \n File file = new File(url.toURI());\n<\/pre>\n\n\n\n
app\/src\/main\/resources\/gradle\/geotools\/shapefiles<\/code>, and put the shapefiles in the shapefiles directory. The countries shapefiles are from data-v1_2.zip<\/code>. You can find the zip file at:<\/p>\n\n\n\nQuery<\/code>.<\/p>\n\n\n\n System.out.println(\"Result from querying for all countries and population\");\n String cqlString = \"include\"; \/\/ Include all features\n Filter filter = CQL.toFilter(cqlString);\n Query query = new Query(typeName, filter, new String[] { \"CNTRY_NAME\", \"POP_CNTRY\" });\n System.out.println(\"query: \" + query + \"\\n\");\n<\/pre>\n\n\n\ntry<\/code><\/strong> and the iterator:<\/p>\n\n\n\n try (SimpleFeatureIterator iterator = features.features()) {\n while (iterator.hasNext()) {\n ...\n }\n }<\/pre>\n\n\n\n\n
build.gradle<\/code>. The GeoTools jars are not located in Maven Central, rather they are located at OSGeo repositories, so we need to add them to the repositories section of build.gradle. <\/p>\n\n\n\n maven {\n url \"https:\/\/repo.osgeo.org\/repository\/snapshot\/\"\n mavenContent {\n snapshotsOnly()\n } \n }\n\n maven {\n url \"https:\/\/repo.osgeo.org\/repository\/release\/\"\n mavenContent {\n releasesOnly()\n }\n }<\/pre>\n\n\n\n String geotoolsVersion = '32-SNAPSHOT'\n \/\/ Provides support for reading and writing shapefiles\n \/\/ Needed to make the data store\n implementation \"org.geotools:gt-shapefile:$geotoolsVersion\"\n\n \/\/ Needed for CQL filters\n implementation \"org.geotools:gt-swing:$geotoolsVersion\"<\/pre>\n\n\n\n
App.java<\/code> are found in the gt-shapefile package. The gt-swing package is only required for org.geotools.filter.text.cql2.CQL<\/code>. Otherwise gt-swing contains classes for building GUIs. <\/p>\n\n\n\n.\/gradlew run<\/pre>\n\n\n\n
grails-beans<\/h1>\n\n\n\n
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conf\/spring\/resources.groovy<\/code><\/p>\n\n\n\n\n
grails create-app grails-bean<\/pre>\n\n\n\n
src\/main\/groovy\/grails\/bean\/MyBean.groovy<\/pre>\n\n\n\n
package grails.bean \/\/ Don't forget!\n\n\/*\n * A simple bean to demonstrate instantiation, injection and use in Grails.\n * See conf\/spring\/resources.groovy for instantiation.\n * See BootStrap.groovy for injection and use.\n *\/\nclass MyBean {\n String name\n private String constructorName\n\n MyBean(String constructorName) {\n println \"In MyBean constructor\"\n this.constructorName = constructorName\n }\n\n void printName() {\n println \"MyBean name: ${name}\"\n }\n\n void printConstructorName() {\n println \"MyBean constructorName: ${constructorName}\"\n }\n}<\/pre>\n\n\n\nname<\/code> and constructorName<\/code>, and two methods to print the attributes. Note that constructorName<\/code> attribute is set by the constructor, while the name<\/code> attribute is public, so can be set by anyone. <\/p>\n\n\n\ngrails-app\/conf\/spring\/resource.groovy<\/code><\/p>\n\n\n\nimport grails.bean.MyBean\n\n\/*\n * beans registers and instantiates beans.\n * See https:\/\/docs.grails.org\/6.2.0\/guide\/spring.html for simple examples.\n * See https:\/\/stackoverflow.com\/questions\/22400078\/inject-constructor-argument-spring-resource-file-with-grails-groovy\n * for how to inject constructor arguments.\n *\/\n\nbeans = {\n \/\/ This closure uses Spring Domain Specific Language (DSL).\n \/\/ The first argument is the class name and following argument are the constructor arguments\n myBean(MyBean, \"My_Bean_Constructor\") {\n \/\/ Here public variables are set\n name = \"My_Bean\"\n }\n}<\/pre>\n\n\n\n