Spring了解YAML中的属性

Question

Did Spring abandon YAML to use as an alternative to .properties / .xml because of:

[Spring Developer]: ...YAML was considered, but we thought that counting whitespace significant was a support nightmare in the making... [reference from spring forum ]

I am confident YAML makes a lot of sense for properties, and I am using it currently on the project, but have difficulties to inject properties in a

<property name="productName" value="${client.product.name}" />

fashion.

Anything I am missing, or I should create a custom YamlPropertyPlaceholderConfigurer ?

Answer 1

I don't know if this is a bit too late but no - you don't have to implement whole YamlPropertyPlaceholderConfigurer instead you can simply create custom PropertiesPersister and add it as optional parameter.

Here's how your configuration will look

<bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
    <property name="locations">
        <value>file:///C:/somewhere/site.yaml</value>
    </property>
    <property name="propertiesPersister" ref="persister"></property>
</bean>
<bean id="persister" class="com.foo.utils.YamlPropertiesPersister"></bean>

And here's bare-bone (read-only) implementation using SnakeYaml, feel free to add what you need including error handling

public class YamlPropertiesPersister implements PropertiesPersister {
@Override
public void load(Properties props, InputStream is) throws IOException {
    load(props, new InputStreamReader(is));
}

/**
 * We want to traverse map representing Yaml object and each time we find String=String pair we want to
 * save it as Property. As we are going deeper into map we generate compound key as path-like String
 * 
 * @param props
 * @param reader
 * @throws IOException
 * @see org.springframework.util.PropertiesPersister#load(java.util.Properties, java.io.Reader)
 */
@Override
public void load(Properties props, Reader reader) throws IOException {
    Yaml yaml = CollectorUtils.instanceOfYaml();
    Map<String, Object> map = (Map<String, Object>) yaml.load(reader);
    // now we can populate supplied props
    assignProperties(props, map, null);
}

/**
 * @param props
 * @param map
 */
public void assignProperties(Properties props, Map<String, Object> map, String path) {
    for (Entry<String, Object> entry : map.entrySet()) {
        String key = entry.getKey();
        if (StringUtils.isNotEmpty(path))
            key = path + "." + key;
        Object val = entry.getValue();
        if (val instanceof String) {
            // see if we need to create a compound key
            props.put(key, val);
        } else if (val instanceof Map) {
            assignProperties(props, (Map<String, Object>) val, key);
        }
    }
}

@Override
public void store(Properties props, OutputStream os, String header) throws IOException {
    throw new NotImplementedException("Current implementation is a read-only");
}

@Override
public void store(Properties props, Writer writer, String header) throws IOException {
    throw new NotImplementedException("Current implementation is a read-only");
}

@Override
public void loadFromXml(Properties props, InputStream is) throws IOException {
    throw new NotImplementedException("Use DefaultPropertiesPersister if you want to read/write XML");
}

@Override
public void storeToXml(Properties props, OutputStream os, String header) throws IOException {
    throw new NotImplementedException("Use DefaultPropertiesPersister if you want to load/store to XML");
}

@Override
public void storeToXml(Properties props, OutputStream os, String header, String encoding) throws IOException {
    throw new NotImplementedException("Use DefaultPropertiesPersister if you want to read/write XML");
}
}

As added benefit - here's how I create Yaml instance

    public static Yaml instanceOfYaml() {
    DumperOptions options = new DumperOptions();
    options.setDefaultFlowStyle(DumperOptions.FlowStyle.BLOCK);
    options.setDefaultScalarStyle(ScalarStyle.DOUBLE_QUOTED);
    final Yaml yaml = new Yaml(new Loader(), new Dumper(options), new Resolver() {
        /**
         * @see org.yaml.snakeyaml.resolver.Resolver#addImplicitResolvers()
         */
        @Override
        protected void addImplicitResolvers() {
            addImplicitResolver(Tag.BOOL, BOOL, "yYnNtTfFoO");
            // disable resolving of floats and integers
            // addImplicitResolver(Tags.FLOAT, FLOAT, "-+0123456789.");
            // addImplicitResolver(Tag.INT, INT, "-+0123456789");
            addImplicitResolver(Tag.MERGE, MERGE, "<");
            addImplicitResolver(Tag.NULL, NULL, "~nN\0");
            addImplicitResolver(Tag.NULL, EMPTY, null);
            addImplicitResolver(Tag.TIMESTAMP, TIMESTAMP, "0123456789");
            addImplicitResolver(Tag.VALUE, VALUE, "=");
        }
    });
    return yaml;
}

You can also read this in my blog

Answer 2

For those using Spring 3.1, you can register a Yaml PropetySource. The SnakeYaml code is from the Bostone code (thanks) adapted to new PropertySource system of Spring 3.1.

import com.google.common.base.Preconditions;
import org.springframework.core.env.PropertiesPropertySource;
import org.springframework.core.io.Resource;
import org.springframework.util.StringUtils;
import org.yaml.snakeyaml.Dumper;
import org.yaml.snakeyaml.DumperOptions;
import org.yaml.snakeyaml.DumperOptions.ScalarStyle;
import org.yaml.snakeyaml.Loader;
import org.yaml.snakeyaml.Yaml;
import org.yaml.snakeyaml.nodes.Tag;
import org.yaml.snakeyaml.resolver.Resolver;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Properties;

/**
 * @author Sebastien Lorber <i>(lorber.sebastien@gmail.com)</i>
 */
public class YamlPropertiesSource extends PropertiesPropertySource {


  public YamlPropertiesSource(String name, Resource yamlResource) {
    super(name, getPropertySource(yamlResource) );
  }

  private static Properties getPropertySource(Resource yamlResource) {
    Preconditions.checkArgument(yamlResource != null,"no yaml resource provided");
    try {
      InputStream is = yamlResource.getInputStream();
      Properties properties = new Properties();
      load(properties, is);
      return properties;
    } catch ( Exception e ) {
      throw new IllegalStateException("Can't get PropertySource from YAML resource=" + yamlResource,e);
    }
  }

  private static void load(Properties props, InputStream is) throws IOException {
    load(props, new InputStreamReader(is));
  }

  private static void load(Properties props, Reader reader) throws IOException {
    Yaml yaml = instanceOfYaml();
    @SuppressWarnings("unchecked")
    Map<String, Object> map = (Map<String, Object>) yaml.load(reader);
    // now we can populate supplied props
    assignProperties(props, map, null);
  }

  private static void assignProperties(Properties props, Map<String, Object> map, String path) {
    for (Entry<String, Object> entry : map.entrySet()) {
      String key = entry.getKey();
      if ( StringUtils.hasLength(path) )
        key = path + "." + key;
      Object val = entry.getValue();
      if (val instanceof String) {
        // see if we need to create a compound key
        props.put(key, val);
      } else if (val instanceof Map) {
        assignProperties(props, (Map<String, Object>) val, key);
      }
    }
  }

  public static Yaml instanceOfYaml() {
    DumperOptions options = new DumperOptions();
    options.setDefaultFlowStyle(DumperOptions.FlowStyle.BLOCK);
    options.setDefaultScalarStyle(ScalarStyle.DOUBLE_QUOTED);
    final Yaml yaml = new Yaml(new Loader(), new Dumper(options), new Resolver() {
      /**
       * @see org.yaml.snakeyaml.resolver.Resolver#addImplicitResolvers()
       */
      @Override
      protected void addImplicitResolvers() {
        addImplicitResolver(Tag.BOOL, BOOL, "yYnNtTfFoO");
        // disable resolving of floats and integers
        // addImplicitResolver(Tags.FLOAT, FLOAT, "-+0123456789.");
        // addImplicitResolver(Tag.INT, INT, "-+0123456789");
        addImplicitResolver(Tag.MERGE, MERGE, "<");
        addImplicitResolver(Tag.NULL, NULL, "~nN\0");
        addImplicitResolver(Tag.NULL, EMPTY, null);
        addImplicitResolver(Tag.TIMESTAMP, TIMESTAMP, "0123456789");
        addImplicitResolver(Tag.VALUE, VALUE, "=");
      }
    });
    return yaml;
  }

}

Please notice that this is also inspired by ResourcePropertySource, and it loads properties in ISO 8859-1 charset. I opened a bug for that: SPR-10096

You can add this property source to your application context. This can also be done in your unit tests:

public class PropertySourceContextLoader extends GenericXmlContextLoader {
    @Override
    protected void loadBeanDefinitions(GenericApplicationContext context,MergedContextConfiguration mergedConfig) {
        PropertySource<String> ps = new MyPropertySource();
        context.getEnvironment().getPropertySources().addLast(ps);
        super.loadBeanDefinitions(context, mergedConfig);
    }
}

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(loader = PropertySourceContextLoader.class, locations = { "classpath:/spring-application-context.xml" })
public class SpringBasedTest {
         ..........
}

Answer 3

For complete and utter nubs like me who have zero knowledge of what the author is actually doing, but need to do it anyway...here's how I made it work. Have no idea how to de-deprecate the instanceOfYaml() though. One other thing, my Spring Boot Eclipse project read from files marked .yml, not .yaml

import org.springframework.util.PropertiesPersister;
import org.springframework.util.StringUtils;
import org.yaml.snakeyaml.Dumper;
import org.yaml.snakeyaml.DumperOptions;
import org.yaml.snakeyaml.DumperOptions.ScalarStyle;
import org.yaml.snakeyaml.Loader;
import org.yaml.snakeyaml.Yaml;
import org.yaml.snakeyaml.nodes.Tag;
import org.yaml.snakeyaml.resolver.Resolver;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.Reader;
import java.io.Writer;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Properties;

public class YamlPropertiesPersister implements PropertiesPersister {
    @Override
    public void load(Properties props, InputStream is) throws IOException {
        load(props, new InputStreamReader(is));
    }

    /**
     * We want to traverse map representing Yaml object and each time we will find String:String value pair we want to
     * save it as Property. As we are going deeper into map we generate a compound key as path-like String
     *
     * @param props
     * @param reader
     * @throws IOException
     * @see org.springframework.util.PropertiesPersister#load(java.util.Properties, java.io.Reader)
     */
    @Override
    public void load(Properties props, Reader reader) throws IOException {
        Yaml yaml = instanceOfYaml();
        Map<String, Object> map = (Map<String, Object>) yaml.load(reader);
        // now we can populate supplied props
        assignProperties(props, map, null);
    }

    /**
     * @param props
     * @param map
     */
    public void assignProperties(Properties props, Map<String, Object> map, String path) {
        for (Entry<String, Object> entry : map.entrySet()) {
            String key = entry.getKey();
            if (!StringUtils.isEmpty(path))
                key = path + "." + key;
            Object val = entry.getValue();
            if (val instanceof String) {
                // see if we need to create a compound key
                props.put(key, val);
            } else if (val instanceof Map) {
                assignProperties(props, (Map<String, Object>) val, key);
            }
        }
    }

    @Override
    public void store(Properties props, OutputStream os, String header) throws IOException {
        throw new UnsupportedOperationException("Current implementation is a read-only");
    }

    @Override
    public void store(Properties props, Writer writer, String header) throws IOException {
        throw new UnsupportedOperationException("Current implementation is a read-only");
    }

    @Override
    public void loadFromXml(Properties props, InputStream is) throws IOException {
        throw new UnsupportedOperationException("Use DefaultPropertiesPersister if you want to read/write XML");
    }

    @Override
    public void storeToXml(Properties props, OutputStream os, String header) throws IOException {
        throw new UnsupportedOperationException("Use DefaultPropertiesPersister if you want to load/store to XML");
    }

    @Override
    public void storeToXml(Properties props, OutputStream os, String header, String encoding) throws IOException {
        throw new UnsupportedOperationException("Use DefaultPropertiesPersister if you want to read/write XML");
    }


    public static Yaml instanceOfYaml() {
        DumperOptions options = new DumperOptions();
        options.setDefaultFlowStyle(DumperOptions.FlowStyle.BLOCK);
        options.setDefaultScalarStyle(ScalarStyle.DOUBLE_QUOTED);
        final Yaml yaml = new Yaml(new Loader(), new Dumper(options), new Resolver() {
            /**
             * @see org.yaml.snakeyaml.resolver.Resolver#addImplicitResolvers()
             */
            @Override
            protected void addImplicitResolvers() {
                addImplicitResolver(Tag.BOOL, BOOL, "yYnNtTfFoO");
                // disable resolving of floats and integers
                // addImplicitResolver(Tags.FLOAT, FLOAT, "-+0123456789.");
                // addImplicitResolver(Tag.INT, INT, "-+0123456789");
                addImplicitResolver(Tag.MERGE, MERGE, "<");
                addImplicitResolver(Tag.NULL, NULL, "~nN\0");
                addImplicitResolver(Tag.NULL, EMPTY, null);
                addImplicitResolver(Tag.TIMESTAMP, TIMESTAMP, "0123456789");
                addImplicitResolver(Tag.VALUE, VALUE, "=");
            }
        });
        return yaml;
    }
}

Answer 4

The forum post you reference was from the dmServer forum, rather than the Spring Framework, and there's very little relation between the two, so I wouldn't read anything into it.

On top of that, YAML is pretty much unheard of in the Java world, so adding support for it would have been a token gesture (if you'll pardon the expression) at best. XML dominates in Java, especially server-side, so there's little use in swimming against the tide there, especially for a minority format like YAML.

Having said that, writing your own YamlPropertyPlaceholderConfigurer should be easy enough, assuming you can find a YAML parser for Java.