geoserver如何配置样式，使图层使用自定义图片?

<?xml version="1.0" encoding="UTF-8"?>
<StyledLayerDescriptor version="1.0.0"
  xsi:schemaLocation="http://www.opengis.net/sld http://schemas.opengis.net/sld/1.0.0/StyledLayerDescriptor.xsd" xmlns="http://www.opengis.net/sld"
  xmlns:ogc="http://www.opengis.net/ogc" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <NamedLayer>
    <Name>capitals</Name>
    <UserStyle>
      <Name>capitals</Name>
      <Title>Capital cities</Title>
      <FeatureTypeStyle>
        <Rule>
          <Title>Capitals</Title>
          <PointSymbolizer>

            <Graphic>

              要使用自定义图标，必须删除mark标记，即下面的mark部分，蓝色内容。

              <Mark>
                <WellKnownName>circle</WellKnownName>
                <Fill>
                  <CssParameter name="fill">
                    <ogc:Literal>#FF0000</ogc:Literal>
                  </CssParameter>
                </Fill>
                <Stroke>
                  <CssParameter name="stroke">
                    <ogc:Literal>#00FF00</ogc:Literal>
                  </CssParameter>
                  <CssParameter name="stroke-width">
                    <ogc:Literal>2</ogc:Literal>
                  </CssParameter>
                </Stroke>
              </Mark>
              <Opacity>
                <ogc:Literal>1.0</ogc:Literal>
              </Opacity>
              <Size>
                <ogc:Literal>10</ogc:Literal>

              </Size>

             然后添加ExternalGraphic部分，其中：test.png放在GeoServer 2.0.2\data_dir\styles下

              <ExternalGraphic>
                  <OnlineResource xmlns:xlink="http://www.w3.org/1999/xlink" xlink:type="simple" xlink:href="test.png"/>
                  <Format>image/png</Format>
              </ExternalGraphic>
            </Graphic>
          </PointSymbolizer>
        </Rule>
      </FeatureTypeStyle>
    </UserStyle>
  </NamedLayer>
</StyledLayerDescriptor>