使用StaxEventItemWriter构建非平凡的XML文件

问题描述

我需要使用这种结构将某些数据库表的内容转储到XML文件

I need to dump content of some database tables to XML file with this structure

<dump>
  <table name="tableName1">
    <records>
      <record>
        <first column name>value</first column name>
        <second column name>value</second column name>
        <third column name>value</third column name>
      </record>
      <record>...</record>
    </records>
  </table>
  <table name="tableName2">...</table>
</dump>

每个未知的表的实际记录数，因此我无法存储所有数据内存中的单个表和转储到XML。

我的工作现在定义为：

The real number of records for every table in unknown, so I can't store all data for a single table in memory and dump to XML.
My job now is defined as:

<job id="dump-database-job">
  <step id="dumpTables">
  <tasklet>
    <chunk reader="dumpReader" processor="dumpProcessor" writer="dumpWriter" commit-interval="100" />
  </tasklet>
  </step>
</job>

<bean name="dumpProcessor" class="RecordBeanToJaxbElementProcessor" />
<bean name="dumpReader" class="CompositeItemReader">
  <property name="delegates">
  <array>
    <ref bean="TABLE_ONE_Reader" />
    <ref bean="TABLE_TWO_Reader" />
    <ref bean="TABLE_NTH_Reader" />
    <!-- Other delegates omitted,one for table,for brevity... -->
  </array>
  </property>
  <property name="name" value="dumpReader" />
</bean>

<bean name="TABLE_ONE_Reader" class="JdbcCursorItemReader">
  <property name="rowMapper">
    <bean name="rowMapper" class="RecordBeanRowMapper">
      <property name="tableName=" value="TABLE_ONE" />
     </bean>
   </property>
   <!--other mandatory property omitted -->
</bean>

<bean name="dumpWriter" class="StaxEventItemWriter" scope="step">
  <property name="resource" value="file:#{jobParameters['outfile']}" />
  <property name="shouldDeleteIfEmpty" value="true" />
  <property name="marshaller" ref="marshaller" />
  <property name="overwriteOutput" value="true" />
  <property name="rootTagName" value="dump" />
</bean>

<bean name="marshaller" class="org.springframework.oxm.jaxb.Jaxb2Marshaller">
  <property name="supportJaxbElementClass" value="true" />
  <property name="classesToBeBound">
    <array>
      <value>RecordBean</value>
    </array>
  </property>
</bean>

---

---

public class RecordBeanRowMapper implements RowMapper<RecordBean> {
  final static RowMapper<Map<String, Object>> columnMapRowMapper = new ColumnMapRowMapper();
  private String tableName;

  public void setTableName(String tableName) {
    this.tableName = tableName;
  }

  @Override
  public RecordBean mapRow(ResultSet rs, int rowNum) throws SQLException {
    final RecordBean b = new RecordBean();

    b.setTableName(tableName);
    b.setColumnValues(Maps.transformValues(columnMapRowMapper.mapRow(rs, rowNum), new Function<Object, String>()    {
      @Override
      public String apply(Object input) {
        return (input == null ? "NULL" : input.toString();
      }
  }
}

@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement(namespace="")
class RecordBean {
  private String tableName;
  @XmlJavaTypeAdapter
  /* Entries are written using an adapter to write data as
   * <key>value</key>
   * <key>value</key>
   * ...
   */
  public Map<String,String> entries = new HashMap<String,String>();
}

/* Use to build item node name using dynamic tableName as
 * <tableName>
 *   <key>value</key>
 *   <key>value</key>
 * </tableName>
 */
public class RecordBeanToJaxbElementProcessor implements ItemProcessor<RecordBean, JAXBElement<?>> {
  @Override
  public JAXBElement<?> process(RecordBean item) throws Exception {
    return new JAXBElement<RecordBean>(new QName(item.getTableName()), RecordBean.class, item);
  }
}

---

这项工作不完整，不能满足我的需求，因为输出看起来像

---

This job is incomplete and doesn't cover my needs because the output looks like

<?xml version="1.0" encoding="UTF-8"?>
<dump>
  <!-- First record of table TABLE_ONE -->
  <TABLE_ONE>
    <code>Code one</code>
    <description>A record</description>
    <agomappedtable>xyz</agomappedtable>
    <enumcode>NULL</enumcode>
    <is_persistent>false</is_persistent>
    <keep_history_data>false</keep_history_data>
  </TABLE_ONE>
  <!-- Other tons from TABLE_ONE -->
  <!-- First record of table TABLE_TWO -->
  <TABLE_TWO>
    <code>Code 2</code>
    <description>Another record</description>
    <his_name>no_name</his_name>
  </TABLE_TWO>
  <!-- Other tons from TABLE_TWO -->
  <!-- More tables... -->
</dump>

我想我必须丰富作家和/或marshaller组件以实现我的目标，但我没有'找到了一个很好的方法:(

I think I have to enrich writer and/or marshaller components to achieve my goal, but I haven't found a good way to proceed :(

我的问题是：

如何建立一个开头描述的复杂XML结构，并使作业完全可重启并且内存使用量很少？

推荐答案

[拍摄]来自
这不可能是默认的StaxEventItemWriter。我必须为我的一个项目做类似的事情，并编写了一个自定义的GroupingStaxEventItemWriter。请参阅下面的代码。你需要修改特定用例的openGroup和closeGroup方法。注意，通过直接写入底层java.io.Writer而不是通过XMLEventWriter来关闭分组标记。需要重新启动。

[Taken from spring.io forum]
This isn't possibly with the default StaxEventItemWriter. I had to do something similar for one of my projects and wrote a custom GroupingStaxEventItemWriter. See the code below. You'll need to modify the openGroup and closeGroup method for your particular use case. Note that the grouping tag is closed by directly writing to the underlying java.io.Writer instead of through the XMLEventWriter. This is required for restartability.

public class GroupingStaxEventItemWriter<T> extends StaxEventItemWriter<T> {

    private static final String GROUP_IDENTIFIER = "CURRENT_GROUP";

    private Classifier<T, String> classifier;

    private String currentGroup;

    private XMLEventWriter eventWriter;

    private Writer writer;

    @Override
    public void write(List<? extends T> items) throws XmlMappingException, Exception {
        Map<String, List<T>> itemsGroup = new LinkedHashMap<String, List<T>>();
        for (T item : items) {
            String group = classifier.classify(item);
            if (!itemsGroup.containsKey(group)) {
                itemsGroup.put(group, new ArrayList<T>());
            }
            itemsGroup.get(group).add(item);
        }
        for (String group : itemsGroup.keySet()) {
            if (group == null || !group.equals(currentGroup)) {
                if (currentGroup != null) {
                    closeGroup(currentGroup);
                }
                currentGroup = group;
                if (currentGroup != null) {
                    openGroup(currentGroup);
                }
            }
            super.write(itemsGroup.get(group));
        }
    }

    protected void openGroup(String group) throws XMLStreamException, FactoryConfigurationError {
        String groupTagName = group;
        String groupTagNameSpacePrefix = "";
        String groupTagNameSpace = null;
        if (groupTagName.contains("{")) {
            groupTagNameSpace = groupTagName.replaceAll("\\{(.*)\\}.*", "$1");
            groupTagName = groupTagName.replaceAll("\\{.*\\}(.*)", "$1");
            if (groupTagName.contains(":")) {
                groupTagNameSpacePrefix = groupTagName.replaceAll("(.*):.*", "$1");
                groupTagName = groupTagName.replaceAll(".*:(.*)", "$1");
            }
        }
        XMLEventFactory xmlEventFactory = createXmlEventFactory();
        eventWriter.add(xmlEventFactory.createStartElement(groupTagNameSpacePrefix, groupTagNameSpace, groupTagName));
    }

    protected void closeGroup(String group)
            throws XMLStreamException, FactoryConfigurationError {
        String groupTagName = group;
        String groupTagNameSpacePrefix = "";
        if (groupTagName.contains("{")) {
            groupTagName = groupTagName.replaceAll("\\{.*\\}(.*)", "$1");
            if (groupTagName.contains(":")) {
                groupTagNameSpacePrefix = groupTagName.replaceAll("(.*):.*", "$1") + ":";
                groupTagName = groupTagName.replaceAll(".*:(.*)", "$1");
            }
        }
        try {
            writer.write("</" + groupTagNameSpacePrefix + groupTagName + ">");
        } catch (IOException ioe) {
            throw new DataAccessResourceFailureException("Unable to close group: [" + group + "]", ioe);
        }
    }

    @Override
    protected XMLEventWriter createXmlEventWriter(XMLOutputFactory outputFactory, Writer writer)
            throws XMLStreamException {
        this.writer = writer;
        this.eventWriter = super.createXmlEventWriter(outputFactory, writer);
        return eventWriter;
    }

    @Override
    public void open(ExecutionContext executionContext) {
        if (executionContext.containsKey(getExecutionContextKey(GROUP_IDENTIFIER))) {
            currentGroup = executionContext.getString(getExecutionContextKey(GROUP_IDENTIFIER));
        }
        super.open(executionContext);
    }

    @Override
    public void update(ExecutionContext executionContext) {
        executionContext.putString(getExecutionContextKey(GROUP_IDENTIFIER), currentGroup);
        super.update(executionContext);
    }

    @Override
    public void close() {
        if (currentGroup != null) {
            try {
                closeGroup(currentGroup);
            } catch (XMLStreamException e) {
                throw new ItemStreamException("Failed to write close tag for element: " + currentGroup, e);
            } catch (FactoryConfigurationError e) {
                throw new ItemStreamException("Failed to write close tag for element: " + currentGroup, e);
            }
        }
        super.close();
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        super.afterPropertiesSet();
        Assert.notNull(classifier, "Missing required property 'classifier'");
    }

    public void setClassifier(Classifier<T, String> classifier) {
        this.classifier = classifier;
    }

}

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