如何从Java文件中以字符串形式读取XML内容

Question

I get a text file from my source which has the below content in single line.

<employees><employee><id>101</id><name>Lokesh Gupta</name><title>Author</title></employee><employee><id>102</id><name>Brian Lara</name><title>Cricketer</title></employee></employees>

In my code, I have to read each employee data as String. Eg: <employee><id>101</id><name>Lokesh Gupta</name><title>Author</title></employee> as a string and <employee><id>102</id><name>Brian Lara</name><title>Cricketer</title></employee> as another string. When I print the content on console, it has to print <employee><id>101</id><name>Lokesh Gupta</name><title>Author</title></employee> . Could you please let me know how to do this?

Generally the file I get from my source consists of 100+ million employee details in single line and I have to read all those employee details as individual String and store that in other file. Since the file size is huge, I tried using SAX parser and with that I am able to parse xml content but unable to read the entire data as string.

I tried using SAX Parser and default handler to read this content. But in startElement and EndElement methods, I have to write my logic to append < and > , < and /> respectively. I want to know better way of reading this instead of writing logic to append the Angular brackets.

Answer 1

One way to do this is to use Streaming feature of JaxB which effectivly uses SAX underneath. Here is an example:

 // create JAXBContext for the primer.xsd
        JAXBContext context = JAXBContext.newInstance("primer");

        Unmarshaller unmarshaller = context.createUnmarshaller();

        // purchase order notification callback
        final PurchaseOrders.Listener orderListener = new PurchaseOrders.Listener() {
            public void handlePurchaseOrder(PurchaseOrders purchaseOrders, PurchaseOrderType purchaseOrder) {
                System.out.println("this order will be shipped to "
                        + purchaseOrder.getShipTo().getName());
            }
        };

        // install the callback on all PurchaseOrders instances
        unmarshaller.setListener(new Unmarshaller.Listener() {
            public void beforeUnmarshal(Object target, Object parent) {
                if(target instanceof PurchaseOrders) {
                    ((PurchaseOrders)target).setPurchaseOrderListener(orderListener);
                }
            }

            public void afterUnmarshal(Object target, Object parent) {
                if(target instanceof PurchaseOrders) {
                    ((PurchaseOrders)target).setPurchaseOrderListener(null);
                }
            }
        });

        // create a new XML parser
        SAXParserFactory factory = SAXParserFactory.newInstance();
        factory.setNamespaceAware(true);
        XMLReader reader = factory.newSAXParser().getXMLReader();
        reader.setContentHandler(unmarshaller.getUnmarshallerHandler());

        for (String arg : args) {
            // parse all the documents specified via the command line.
            // note that XMLReader expects an URL, not a file name.
            // so we need conversion.
            reader.parse(new File(arg).toURI().toString());
        }
    }
}

It is taken straight from jaxB samples in jaxb/ri https://github.com/javaee/jaxb-v2/blob/master/jaxb-ri/samples/src/main/samples/streaming-unmarshalling/src/Main.java

The PurchaseOrders.Listener interface is :

public static interface Listener {
        void handlePurchaseOrder(PurchaseOrders purchaseOrders, PurchaseOrderType purchaseOrder);
    }