public abstract class URLConnection
extends Object

Field Summary

Fields
Modifier and Type	Field	Description
`protected boolean`	`allowUserInteraction`	If `true`, this `URL` is being examined in a context in which it makes sense to allow user interactions such as popping up an authentication dialog.
`protected boolean`	`connected`	If `false`, this connection object has not created a communications link to the specified URL.
`protected boolean`	`doInput`	This variable is set by the `setDoInput` method.
`protected boolean`	`doOutput`	This variable is set by the `setDoOutput` method.
`protected long`	`ifModifiedSince`	Some protocols support skipping the fetching of the object unless the object has been modified more recently than a certain time.
`protected URL`	`url`	The URL represents the remote object on the World Wide Web to which this connection is opened.
`protected boolean`	`useCaches`	If `true`, the protocol is allowed to use caching whenever it can.

Constructor Summary

Constructors
Modifier Constructor Description

protected URLConnection(URL url)
Constructs a URL connection to the specified URL.

Method Summary

All Methods Static Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method	Description
`void`	`addRequestProperty(String key, String value)`	Adds a general request property specified by a key-value pair.
`abstract void`	`connect()`	Opens a communications link to the resource referenced by this URL, if such a connection has not already been established.
`boolean`	`getAllowUserInteraction()`	Returns the value of the `allowUserInteraction` field for this object.
`int`	`getConnectTimeout()`	Returns setting for connect timeout.
`String`	`getContentEncoding()`	Returns the value of the `content-encoding` header field.
`int`	`getContentLength()`	Returns the value of the `content-length` header field.
`long`	`getContentLengthLong()`	Returns the value of the `content-length` header field as a long.
`String`	`getContentType()`	Returns the value of the `content-type` header field.
`long`	`getDate()`	Returns the value of the `date` header field.
`static boolean`	`getDefaultAllowUserInteraction()`	Returns the default value of the `allowUserInteraction` field.
`boolean`	`getDefaultUseCaches()`	Returns the default value of a `URLConnection`'s `useCaches` flag.
`boolean`	`getDoInput()`	Returns the value of this `URLConnection`'s `doInput` flag.
`boolean`	`getDoOutput()`	Returns the value of this `URLConnection`'s `doOutput` flag.
`long`	`getExpiration()`	Returns the value of the `expires` header field.
`String`	`getHeaderField(int number)`	Returns the value for the `n`^th header field.
`String`	`getHeaderField(String name)`	Returns the value of the named header field.
`long`	`getHeaderFieldDate(String name, long pdefault)`	Returns the value of the named field parsed as date.
`int`	`getHeaderFieldInt(String name, int pdefault)`	Returns the value of the named field parsed as a number.
`String`	`getHeaderFieldKey(int number)`	Returns the key for the `n`^th header field.
`long`	`getHeaderFieldLong(String name, long pdefault)`	Returns the value of the named field parsed as a number.
`Map<String,List<String>>`	`getHeaderFields()`	Returns an unmodifiable Map of the header fields.
`long`	`getIfModifiedSince()`	Returns the value of this object's `ifModifiedSince` field.
`InputStream`	`getInputStream()`	Returns an input stream that reads from this open connection.
`long`	`getLastModified()`	Returns the value of the `last-modified` header field.
`OutputStream`	`getOutputStream()`	Returns an output stream that writes to this connection.
`int`	`getReadTimeout()`	Returns setting for read timeout. 0 return implies that the option is disabled (i.e., timeout of infinity).
`String`	`getRequestProperty(String key)`	Returns the value of the named general request property for this connection.
`URL`	`getURL()`	Returns the value of this `URLConnection`'s `URL` field.
`boolean`	`getUseCaches()`	Returns the value of this `URLConnection`'s `useCaches` field.
`void`	`setAllowUserInteraction(boolean allowuserinteraction)`	Set the value of the `allowUserInteraction` field of this `URLConnection`.
`void`	`setConnectTimeout(int timeout)`	Sets a specified timeout value, in milliseconds, to be used when opening a communications link to the resource referenced by this URLConnection.
`static void`	`setDefaultAllowUserInteraction(boolean defaultallowuserinteraction)`	Sets the default value of the `allowUserInteraction` field for all future `URLConnection` objects to the specified value.
`void`	`setDefaultUseCaches(boolean defaultusecaches)`	Sets the default value of the `useCaches` field to the specified value.
`void`	`setDoInput(boolean doinput)`	Sets the value of the `doInput` field for this `URLConnection` to the specified value.
`void`	`setDoOutput(boolean dooutput)`	Sets the value of the `doOutput` field for this `URLConnection` to the specified value.
`void`	`setIfModifiedSince(long ifmodifiedsince)`	Sets the value of the `ifModifiedSince` field of this `URLConnection` to the specified value.
`void`	`setReadTimeout(int timeout)`	Sets the read timeout to a specified timeout, in milliseconds.
`void`	`setRequestProperty(String key, String value)`	Sets the general request property.
`void`	`setUseCaches(boolean usecaches)`	Sets the value of the `useCaches` field of this `URLConnection` to the specified value.
`String`	`toString()`	Returns a `String` representation of this URL connection.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- Field Detail
  - url
```
protected URL url
```
    The URL represents the remote object on the World Wide Web to which this connection is opened.
    The value of this field can be accessed by the getURL method.
    
    The default value of this variable is the value of the URL argument in the URLConnection constructor.
    
    See Also:
    
    getURL(), url
  - doInput
```
protected boolean doInput
```
    This variable is set by the setDoInput method. Its value is returned by the getDoInput method.
    A URL connection can be used for input and/or output. Setting the doInput flag to true indicates that the application intends to read data from the URL connection.
    
    The default value of this field is true.
    
    See Also:
    
    getDoInput(), setDoInput(boolean)
  - doOutput
```
protected boolean doOutput
```
    This variable is set by the setDoOutput method. Its value is returned by the getDoOutput method.
    A URL connection can be used for input and/or output. Setting the doOutput flag to true indicates that the application intends to write data to the URL connection.
    
    The default value of this field is false.
    
    See Also:
    
    getDoOutput(), setDoOutput(boolean)
  - allowUserInteraction
```
protected boolean allowUserInteraction
```
    If true, this URL is being examined in a context in which it makes sense to allow user interactions such as popping up an authentication dialog. If false, then no user interaction is allowed.
    The value of this field can be set by the setAllowUserInteraction method. Its value is returned by the getAllowUserInteraction method. Its default value is the value of the argument in the last invocation of the setDefaultAllowUserInteraction method.
    
    See Also:
    
    getAllowUserInteraction(), setAllowUserInteraction(boolean), setDefaultAllowUserInteraction(boolean)
  - useCaches
```
protected boolean useCaches
```
    If true, the protocol is allowed to use caching whenever it can. If false, the protocol must always try to get a fresh copy of the object.
    This field is set by the setUseCaches method. Its value is returned by the getUseCaches method.
    
    Its default value is the value given in the last invocation of the setDefaultUseCaches method.
    
    See Also:
    
    setUseCaches(boolean), getUseCaches(), setDefaultUseCaches(boolean)
  - ifModifiedSince
```
protected long ifModifiedSince
```
    Some protocols support skipping the fetching of the object unless the object has been modified more recently than a certain time.
    A nonzero value gives a time as the number of milliseconds since January 1, 1970, GMT. The object is fetched only if it has been modified more recently than that time.
    
    This variable is set by the setIfModifiedSince method. Its value is returned by the getIfModifiedSince method.
    
    The default value of this field is 0, indicating that the fetching must always occur.
    
    See Also:
    
    getIfModifiedSince(), setIfModifiedSince(long)
  - connected
```
protected boolean connected
```
    If false, this connection object has not created a communications link to the specified URL. If true, the communications link has been established.
- Constructor Detail
  - URLConnection
```
protected URLConnection(URL url)
```
    Constructs a URL connection to the specified URL. A connection to the object referenced by the URL is not created.
    
    Parameters:
    
    url - the specified URL.
- Method Detail
  - connect
```
public abstract void connect()
                      throws IOException
```
    Opens a communications link to the resource referenced by this URL, if such a connection has not already been established.
    If the connect method is called when the connection has already been opened (indicated by the connected field having the value true), the call is ignored.
    
    URLConnection objects go through two phases: first they are created, then they are connected. After being created, and before being connected, various options can be specified (e.g., doInput and UseCaches). After connecting, it is an error to try to set them. Operations that depend on being connected, like getContentLength, will implicitly perform the connection, if necessary.
    
    Throws:
    
    SocketTimeoutException - if the timeout expires before the connection can be established
    
    IOException - if an I/O error occurs while opening the connection.
    
    See Also:
    
    connected, getConnectTimeout(), setConnectTimeout(int)
  - setConnectTimeout
```
public void setConnectTimeout(int timeout)
```
    Sets a specified timeout value, in milliseconds, to be used when opening a communications link to the resource referenced by this URLConnection. If the timeout expires before the connection can be established, a java.net.SocketTimeoutException is raised. A timeout of zero is interpreted as an infinite timeout.
    Some non-standard implementation of this method may ignore the specified timeout. To see the connect timeout set, please call getConnectTimeout().
    
    Parameters:
    
    timeout - an int that specifies the connect timeout value in milliseconds
    
    Throws:
    
    IllegalArgumentException - if the timeout parameter is negative
    
    Since:
    
    1.5
    
    See Also:
    
    getConnectTimeout(), connect()
  - getConnectTimeout
```
public int getConnectTimeout()
```
    Returns setting for connect timeout.
    0 return implies that the option is disabled (i.e., timeout of infinity).
    
    Returns:
    
    an int that indicates the connect timeout value in milliseconds
    
    Since:
    
    1.5
    
    See Also:
    
    setConnectTimeout(int), connect()
  - setReadTimeout
```
public void setReadTimeout(int timeout)
```
    Sets the read timeout to a specified timeout, in milliseconds. A non-zero value specifies the timeout when reading from Input stream when a connection is established to a resource. If the timeout expires before there is data available for read, a java.net.SocketTimeoutException is raised. A timeout of zero is interpreted as an infinite timeout.
    Some non-standard implementation of this method ignores the specified timeout. To see the read timeout set, please call getReadTimeout().
    
    Parameters:
    
    timeout - an int that specifies the timeout value to be used in milliseconds
    
    Throws:
    
    IllegalArgumentException - if the timeout parameter is negative
    
    Since:
    
    1.5
    
    See Also:
    
    getReadTimeout(), InputStream.read()
  - getReadTimeout
```
public int getReadTimeout()
```
    Returns setting for read timeout. 0 return implies that the option is disabled (i.e., timeout of infinity).
    
    Returns:
    
    an int that indicates the read timeout value in milliseconds
    
    Since:
    
    1.5
    
    See Also:
    
    setReadTimeout(int), InputStream.read()
  - setRequestProperty
```
public void setRequestProperty(String key,
                               String value)
```
    Sets the general request property. If a property with the key already exists, overwrite its value with the new value.
    NOTE: HTTP requires all request properties which can legally have multiple instances with the same key to use a comma-separated list syntax which enables multiple properties to be appended into a single property.
    
    Parameters:
    
    key - the keyword by which the request is known (e.g., "Accept").
    
    value - the value associated with it.
    
    Throws:
    
    IllegalStateException - if already connected
    
    NullPointerException - if key is null
    
    See Also:
    
    getRequestProperty(java.lang.String)
  - addRequestProperty
```
public void addRequestProperty(String key,
                               String value)
```
    Adds a general request property specified by a key-value pair. This method will not overwrite existing values associated with the same key.
    
    Parameters:
    
    key - the keyword by which the request is known (e.g., "Accept").
    
    value - the value associated with it.
    
    Throws:
    
    IllegalStateException - if already connected
    
    NullPointerException - if key is null
    
    Since:
    
    1.4
    
    See Also:
    
    #getRequestProperties()
  - getRequestProperty
```
public String getRequestProperty(String key)
```
    Returns the value of the named general request property for this connection.
    
    Parameters:
    
    key - the keyword by which the request is known (e.g., "Accept").
    
    Returns:
    
    the value of the named general request property for this connection. If key is null, then null is returned.
    
    Throws:
    
    IllegalStateException - if already connected
    
    See Also:
    
    setRequestProperty(java.lang.String, java.lang.String)
  - getURL
```
public URL getURL()
```
    Returns the value of this URLConnection's URL field.
    
    Returns:
    
    the value of this URLConnection's URL field.
    
    See Also:
    
    url
  - getContentLength
```
public int getContentLength()
```
    Returns the value of the content-length header field.
    Note: getContentLengthLong() should be preferred over this method, since it returns a long instead and is therefore more portable.
    
    Returns:
    
    the content length of the resource that this connection's URL references, -1 if the content length is not known, or if the content length is greater than Integer.MAX_VALUE.
  - getContentLengthLong
```
public long getContentLengthLong()
```
    Returns the value of the content-length header field as a long.
    
    Returns:
    
    the content length of the resource that this connection's URL references, or -1 if the content length is not known.
    
    Since:
    
    7.0
  - getContentType
```
public String getContentType()
```
    Returns the value of the content-type header field.
    
    Returns:
    
    the content type of the resource that the URL references, or null if not known.
    
    See Also:
    
    getHeaderField(java.lang.String)
  - getContentEncoding
```
public String getContentEncoding()
```
    Returns the value of the content-encoding header field.
    
    Returns:
    
    the content encoding of the resource that the URL references, or null if not known.
    
    See Also:
    
    getHeaderField(java.lang.String)
  - getExpiration
```
public long getExpiration()
```
    Returns the value of the expires header field.
    
    Returns:
    
    the expiration date of the resource that this URL references, or 0 if not known. The value is the number of milliseconds since January 1, 1970 GMT.
    
    See Also:
    
    getHeaderField(java.lang.String)
  - getDate
```
public long getDate()
```
    Returns the value of the date header field.
    
    Returns:
    
    the sending date of the resource that the URL references, or 0 if not known. The value returned is the number of milliseconds since January 1, 1970 GMT.
    
    See Also:
    
    getHeaderField(java.lang.String)
  - getLastModified
```
public long getLastModified()
```
    Returns the value of the last-modified header field. The result is the number of milliseconds since January 1, 1970 GMT.
    
    Returns:
    
    the date the resource referenced by this URLConnection was last modified, or 0 if not known.
    
    See Also:
    
    getHeaderField(java.lang.String)
  - getHeaderField
```
public String getHeaderField(String name)
```
    Returns the value of the named header field.
    If called on a connection that sets the same header multiple times with possibly different values, only the last value is returned.
    
    Parameters:
    
    name - the name of a header field.
    
    Returns:
    
    the value of the named header field, or null if there is no such field in the header.
  - getHeaderField
```
public String getHeaderField(int number)
```
    Returns the value for the n^th header field. It returns null if there are fewer than n+1fields.
    This method can be used in conjunction with the getHeaderFieldKey method to iterate through all the headers in the message.
    
    Parameters:
    
    number - an index, where n>=0
    
    Returns:
    
    the value of the n^th header field or null if there are fewer than n+1 fields
    
    See Also:
    
    getHeaderFieldKey(int)
  - getHeaderFields
```
public Map<String,List<String>> getHeaderFields()
```
    Returns an unmodifiable Map of the header fields. The Map keys are Strings that represent the response-header field names. Each Map value is an unmodifiable List of Strings that represents the corresponding field values.
    
    Returns:
    
    a Map of header fields
    
    Since:
    
    1.4
  - getHeaderFieldInt
```
public int getHeaderFieldInt(String name,
                             int pdefault)
```
    Returns the value of the named field parsed as a number.
    This form of getHeaderField exists because some connection types (e.g., http-ng ) have pre-parsed headers. Classes for that connection type can override this method and short-circuit the parsing.
    
    Parameters:
    
    name - the name of the header field.
    
    pdefault - the default value.
    
    Returns:
    
    the value of the named field, parsed as an integer. The Default value is returned if the field is missing or malformed.
  - getHeaderFieldLong
```
public long getHeaderFieldLong(String name,
                               long pdefault)
```
    Returns the value of the named field parsed as a number.
    This form of getHeaderField exists because some connection types (e.g., http-ng ) have pre-parsed headers. Classes for that connection type can override this method and short-circuit the parsing.
    
    Parameters:
    
    name - the name of the header field.
    
    pdefault - the default value.
    
    Returns:
    
    the value of the named field, parsed as a long. The Default value is returned if the field is missing or malformed.
    
    Since:
    
    7.0
  - getHeaderFieldDate
```
public long getHeaderFieldDate(String name,
                               long pdefault)
```
    Returns the value of the named field parsed as date. The result is the number of milliseconds since January 1, 1970 GMT represented by the named field.
    This form of getHeaderField exists because some connection types (e.g., http-ng ) have pre-parsed headers. Classes for that connection type can override this method and short-circuit the parsing.
    
    Parameters:
    
    name - the name of the header field.
    
    pdefault - a default value.
    
    Returns:
    
    the value of the field, parsed as a date. The value of the Default argument is returned if the field is missing or malformed.
  - getHeaderFieldKey
```
public String getHeaderFieldKey(int number)
```
    Returns the key for the n^th header field. It returns null if there are fewer than n+1 fields.
    
    Parameters:
    
    number - an index, where n>=0
    
    Returns:
    
    the key for the n^th header field, or null if there are fewer than n+1 fields.
  - getInputStream
```
public InputStream getInputStream()
                           throws IOException
```
    Returns an input stream that reads from this open connection.
    A SocketTimeoutException can be thrown when reading from the returned input stream if the read timeout expires before data is available for read.
    
    Returns:
    
    an input stream that reads from this open connection.
    
    Throws:
    
    IOException - if an I/O error occurs while creating the input stream.
    
    UnknownServiceException - if the protocol does not support input.
    
    See Also:
    
    setReadTimeout(int), getReadTimeout()
  - getOutputStream
```
public OutputStream getOutputStream()
                             throws IOException
```
    Returns an output stream that writes to this connection.
    
    Returns:
    
    an output stream that writes to this connection.
    
    Throws:
    
    IOException - if an I/O error occurs while creating the output stream.
    
    UnknownServiceException - if the protocol does not support output.
  - toString
```
public String toString()
```
    Returns a String representation of this URL connection.
    
    Overrides:
    
    toString in class Object
    
    Returns:
    
    a string representation of this URLConnection.
  - setDoInput
```
public void setDoInput(boolean doinput)
```
    Sets the value of the doInput field for this URLConnection to the specified value.
    A URL connection can be used for input and/or output. Set the DoInput flag to true if you intend to use the URL connection for input, false if not. The default is true.
    
    Parameters:
    
    doinput - the new value.
    
    Throws:
    
    IllegalStateException - if already connected
    
    See Also:
    
    doInput, getDoInput()
  - getDoInput
```
public boolean getDoInput()
```
    Returns the value of this URLConnection's doInput flag.
    
    Returns:
    
    the value of this URLConnection's doInput flag.
    
    See Also:
    
    setDoInput(boolean)
  - setDoOutput
```
public void setDoOutput(boolean dooutput)
```
    Sets the value of the doOutput field for this URLConnection to the specified value.
    A URL connection can be used for input and/or output. Set the DoOutput flag to true if you intend to use the URL connection for output, false if not. The default is false.
    
    Parameters:
    
    dooutput - the new value.
    
    Throws:
    
    IllegalStateException - if already connected
    
    See Also:
    
    getDoOutput()
  - getDoOutput
```
public boolean getDoOutput()
```
    Returns the value of this URLConnection's doOutput flag.
    
    Returns:
    
    the value of this URLConnection's doOutput flag.
    
    See Also:
    
    setDoOutput(boolean)
  - setAllowUserInteraction
```
public void setAllowUserInteraction(boolean allowuserinteraction)
```
    Set the value of the allowUserInteraction field of this URLConnection.
    
    Parameters:
    
    allowuserinteraction - the new value.
    
    Throws:
    
    IllegalStateException - if already connected
    
    See Also:
    
    getAllowUserInteraction()
  - getAllowUserInteraction
```
public boolean getAllowUserInteraction()
```
    Returns the value of the allowUserInteraction field for this object.
    
    Returns:
    
    the value of the allowUserInteraction field for this object.
    
    See Also:
    
    setAllowUserInteraction(boolean)
  - setDefaultAllowUserInteraction
```
public static void setDefaultAllowUserInteraction(boolean defaultallowuserinteraction)
```
    Sets the default value of the allowUserInteraction field for all future URLConnection objects to the specified value.
    
    Parameters:
    
    defaultallowuserinteraction - the new value.
    
    See Also:
    
    getDefaultAllowUserInteraction()
  - getDefaultAllowUserInteraction
```
public static boolean getDefaultAllowUserInteraction()
```
    Returns the default value of the allowUserInteraction field.
    Ths default is "sticky", being a part of the static state of all URLConnections. This flag applies to the next, and all following URLConnections that are created.
    
    Returns:
    
    the default value of the allowUserInteraction field.
    
    See Also:
    
    setDefaultAllowUserInteraction(boolean)
  - setUseCaches
```
public void setUseCaches(boolean usecaches)
```
    Sets the value of the useCaches field of this URLConnection to the specified value.
    Some protocols do caching of documents. Occasionally, it is important to be able to "tunnel through" and ignore the caches (e.g., the "reload" button in a browser). If the UseCaches flag on a connection is true, the connection is allowed to use whatever caches it can. If false, caches are to be ignored. The default value comes from DefaultUseCaches, which defaults to true.
    
    Parameters:
    
    usecaches - a boolean indicating whether or not to allow caching
    
    Throws:
    
    IllegalStateException - if already connected
    
    See Also:
    
    getUseCaches()
  - getUseCaches
```
public boolean getUseCaches()
```
    Returns the value of this URLConnection's useCaches field.
    
    Returns:
    
    the value of this URLConnection's useCaches field.
    
    See Also:
    
    setUseCaches(boolean)
  - setIfModifiedSince
```
public void setIfModifiedSince(long ifmodifiedsince)
```
    Sets the value of the ifModifiedSince field of this URLConnection to the specified value.
    
    Parameters:
    
    ifmodifiedsince - the new value.
    
    Throws:
    
    IllegalStateException - if already connected
    
    See Also:
    
    getIfModifiedSince()
  - getIfModifiedSince
```
public long getIfModifiedSince()
```
    Returns the value of this object's ifModifiedSince field.
    
    Returns:
    
    the value of this object's ifModifiedSince field.
    
    See Also:
    
    setIfModifiedSince(long)
  - getDefaultUseCaches
```
public boolean getDefaultUseCaches()
```
    Returns the default value of a URLConnection's useCaches flag.
    Ths default is "sticky", being a part of the static state of all URLConnections. This flag applies to the next, and all following URLConnections that are created.
    
    Returns:
    
    the default value of a URLConnection's useCaches flag.
    
    See Also:
    
    setDefaultUseCaches(boolean)
  - setDefaultUseCaches
```
public void setDefaultUseCaches(boolean defaultusecaches)
```
    Sets the default value of the useCaches field to the specified value.
    
    Parameters:
    
    defaultusecaches - the new value.
    
    See Also:
    
    getDefaultUseCaches()

Class URLConnection

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

url

doInput

doOutput

allowUserInteraction

useCaches

ifModifiedSince

connected

Constructor Detail

URLConnection

Method Detail

connect

setConnectTimeout

getConnectTimeout

setReadTimeout

getReadTimeout

setRequestProperty

addRequestProperty

getRequestProperty

getURL

getContentLength

getContentLengthLong

getContentType

getContentEncoding

getExpiration

getDate

getLastModified

getHeaderField

getHeaderField

getHeaderFields

getHeaderFieldInt

getHeaderFieldLong

getHeaderFieldDate

getHeaderFieldKey

getInputStream

getOutputStream

toString

setDoInput

getDoInput

setDoOutput

getDoOutput

setAllowUserInteraction

getAllowUserInteraction

setDefaultAllowUserInteraction

getDefaultAllowUserInteraction

setUseCaches

getUseCaches

setIfModifiedSince

getIfModifiedSince

getDefaultUseCaches

setDefaultUseCaches