Several methods of accessing program status - Java IO application talks

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It has not been taken from Blog for more than a month. For example, the projects of the laboratory are collecting work, huge, such as finding work and related things; and in February is to accompany the old man, the speed of the family It is imaginable that ... but mainly did not find a suitable Topic, or this time is lazy (Proqi syndrome), net is watching the "Hanwu Emperor" and historical books, and other messy Jiaste, just play Java seriously, haha! Now work is almost implemented, so good is not too bad, and the life of the small-breasted young Jungleford starts to enter the right track! The above is some nonsense in the New Year. Today, I will talk about "program status saving" aspects. We can easily think of "serialization" (serialization, and "sequentialization" or "serialization", but "serial" The word always let me think of communication and hardware interface, so I am more accustomed to "serialization" called, let alone this name is coming, and I will talk about the origin of this name), of course, serialization It is a convenient and effective data access method, but it also has a wider range of applications. In general, it is to discuss some of I / O applications.

File I / O: Files → Serialization

★ File stream file operation is the simplest and most exclusive way, we said that the file operation is not just a "naked" way through FileInputStream / FileOutputStream to write data directly to the local file (like I used to write A mine-mine game Javamine is to save a state of the situation, which is compared to the "underlying".

Main Class and Method Description FileInputStream.Read () Read Data Data from Local File FileReader.Read () Readput (text) Data FileoutputStream.write () Save Binary Data to Local File FileWriter.write () Save Character Data to Local Files

★ XML and the above simple I / O mode, XML look much "high-grade", so that it is a standard for data exchange. Take the DOM way, it cares about constructing a document tree in memory, and the data is saved on a node (which can be a leaf node, or the attribute of the label node), the construction of the next one Write an external file, but we only need to know the location of the file, do not know how I / O operation, the XML operation method may also practice more people, so only list related methods, for beginners Learn about. The main package is javax.xml.parsers, org.w3c.dom, javax.xml.transform.

The main classes and methods described DocumentBuilderFactory.newDocumentBuilder (). Parse () parsing an external XML file, to obtain a tree of DOM Document object DocumentBuilderFactory.newInstance (). NewDocumentBuilder (). NewDocument () to initialize a DOM tree Document.getDocumentElement ( ). Appendchild () Add a sub-node to a tag node Document.createTextNode () Generate a string node node.getChildNodes () get a node all the next layer node.removeChild () Delete Subnation Document. GetElementsBytagname () Find all the tag nodes of all specified names Document.getElementById () Find a tag node of the specified name, if there is a plurality of conformity, return to one, usually the first Element.getaTribute () gets a value of a label Element.setttribute () Sets the value of a label for Element.RemoveAttribute () deletes a tag for a property transformerfactory.newinStance (). NewTransformer () .transform () Write a DOM tree into an external XML file ★ Serialization uses basic file read and write mode access data, if we only save the same type of data, you can save it in the same format, for example When I saved a disk in my javamine, you need to save each checkered coordinate, whether there is mine, whether it is opened, etc., which combines these information into a "composite type"; reverse, if there are a variety of different types of data, Then we either break it into a number of parts, saved with the same type (such as String), or we need to add logic that resolves different types of data formats in the program, which is inconvenient. So we expect to handle data with a higher level of "high" level, programmers should resolve data as little time and code, in fact, serialization operations provide us with such a way. Serialization may have contact, which can write objects in a particular coded format or read from external byte streams (ie ObjectInputStream / ObjectOutputStream). Serialized an object is very simple, just implement the serializable interface, or even use it for it to add any way:

Public class myserial imports java.io.serializable {...}

But there is a condition: that is, you have to serialize, each attribute must be "sequentially". This sentence is a bit 拗, in fact, all basic types (which are int, char, boolean, "can be sequentially", and you can look at the JDK documentation, will find that many classes have already implemented serializable (ie It is already "sequential"), so these types of objects and basic data types can be directly used as internal properties that you need sequence. What should I do if I have encountered an attribute of "sequentialization"? Sorry, the class of this property also needs to implement the Serializable interface in advance, so that all attributes are "sequentially".

Main Class and Method Description ObjectOutputStream.WriteObject () Sequence an object to external byte stream ObjectInputStream.readObject () read from external byte stream and restructuring the object from the actual application, "serializable" interface is not Define any way, as if it is just a tag (or a keyword like Java), once the virtual machine sees this "tag", try calling the pre-predefined serialization mechanism unless you are implementing the Serializable interface The private readObject () or WriteObject () method is also defined. This is very strange. But if you are not willing to let the system use the default way to serialize, you must define the two methods mentioned above:

public class MySerial implements java.io.Serializable {private void writeObject (java.io.ObjectOutputStream out) throws IOException {...} private void readObject (java.io.ObjectInputStream in) throws IOException, ClassNotFoundException {...} .. }

For example, you can call the default serialization method ObjectOutputStream.defaultWriteObject () in WriteObject (); for example, you don't want to use some sensitive properties and information serialization, you can also call the objectOutputStream.writeObject () method to clearly specify the needs. Serialized those properties. With regard to user customized serialization, we will mention later.

★ The serialization above the bean is just a basic application. After you sequence the object to the external file, open the file with notepad, you can only guess this is about this class from some readable characters. Document, this requires you to be familiar with the byte coding method of serialized files, which will be more painful (in the first volume of "Core Java 2", if you are interested, you can check the reference information, some cases We may need to be serialized with better readability. On the other hand, as the core concept "javabeans" as a Java component, starting from JDK 1.4, the "long-term persistence" (long-term persistence "(long-term persistence" is required to support text mode is also required. Open the JDK document, there is a class named "Encoder" in the java.beans package, which is a practical class that can serialize the bean. And it is related to the two major classes with XMlecoder and Xmldecoder, apparently, which is a tool for saving and reading Bean with XML file format. Their usage is also very simple, and it is similar to ObjectOutputStream / ObjectInputStream / ObjectInputStream.

Main Class and Method Description XmlenCoder.writeObject () Sequence an object to external byte stream Xmldecoder.ReadObject () read from external byte stream and restructively

If a bean is in the following format:

Public class mybean {INT i; char [] c; string s; ... (GET and SET operation omitted) ...}

Then the XML file serialized through XMlecoder has this form:

a B c < / void> fox jump! Many visual components like AWT and SWING are bean, of course, can be used Sequence is serialized, the following is an XML file after the JFRAME serialization extracted from the JDK document:

frame1 0 0 200